nutrition

Family Health Steps to take to create a healthy home.

More about Nutrition: Origins Purpose Preparations Precautions Side effects Research and general acceptance Resources

Definition

Good nutrition can help prevent disease and promote health. There are six categories of nutrients that the body needs to acquire from food: protein, carbohydrates, fat, fibers, vitamins and minerals, and water.

Protein supplies amino acids to build and maintain healthy body tissue. There are 20 amino acids considered essential because the body must have all of them in the right amounts to function properly. Twelve of these are manufactured in the body but the other eight amino acids must be provided by the diet. Foods from animal source such as milk or eggs often contain all these essential amino acids while a variety of plant products must be taken together to provide all these necessary protein components.

Fat supplies energy and transports nutrients. There are two families of fatty acids considered essential for the body: the omega-3 and omega-6 fatty acids. Essential fatty acids are required by the body to function normally. They can be obtained from canola oil, flaxseed oil, cold-water fish, or fish oil, all of which contain omega-3 fatty acids, and primrose or black currant seed oil, which contains omega-6 fatty acids. The American diet often contains excess of omega-6 fatty acids and insufficient amount of omega-3 fats. Increased consumption of omega-3 oils are recommended to help reduce risk of cardiovascular diseases and cancer and alleviate symptoms of rheumatoid arthritis, premenstrual syndrome, dermatitis, and inflammatory bowel disease.

Carbohydrates are the body's main source of energy and should be the major part of total daily intake. There are two types of carbohydrates: simple carbohydrates (such as sugar or honey) or complex carbohydrates (such as grains, beans, peas, or potatoes). Complex carbohydrates are preferred because these foods are more nutritious yet have fewer calories per gram compared to fat and cause fewer problems with overeating than fat or sugar. Complex carbohydrates are also preferred over simple carbohydrates by diabetics because they allow better blood glucose control.

Fiber is the material that gives plant texture and support. Although it is primarily made up of carbohydrates, it does not have a lot of calories and usually is not broken down by the body for energy. Dietary fiber is found in plant foods such as fruits, vegetables, legumes, nuts, and whole grains.

There are two types of fiber: soluble and insoluble. Insoluble fiber, as the name implies, does not dissolve in water because it contains high amount of cellulose. Insoluble fiber can be found in the bran of grains, the pulp of fruit and the skin of vegetables. Soluble fiber is the type of fiber that dissolves in water. It can be found in a variety of fruits and vegetables such as apples, oatmeal and oat bran, rye flour, and dried beans.

Although they share some common characteristics such as being partially digested in the stomach and intestines and have few calories, each type of fiber has its own specific health benefits. Insoluble fiber speeds up the transit of foods through the digestive system and adds bulk to the stools, therefore, it is the type of fiber that helps treat constipation or diarrhea and prevents colon cancer. On the other hand, only soluble fiber can lower blood cholesterol levels. This type of fiber works by attaching itself to the cholesterol so that it can be eliminated from the body. This prevents cholesterol from recirculating and being reabsorbed into the bloodstream.

Vitamins are organic substances present in food and required by the body in a minute amount for regulation of metabolism and maintenance of normal growth and functioning. The most commonly known vitamins are A, B₁ (thiamine), B₂ (riboflavin), B₃ (niacin), B₅ (pantothenic acid), B₆ (pyridoxine), B₇ (biotin), B₉ (folic acid), B₁₂ (cobalamin), C (ascorbic acid), D, E, and K. The B and C vitamins are water-soluble, excess amounts of which are excreted in the urine. The A, D, E, and K vitamins are fatsoluble and will be stored in the body fat.

Minerals are vital to our existence because they are the building blocks that make up muscles, tissues, and bones. They also are important components of many life-supporting systems, such as hormones, oxygen transport, and enzyme systems.

There are two kinds of minerals: the major (or macro) minerals and the trace minerals. Major minerals are the minerals that the body needs in large amount. The following minerals are classified as major: calcium, phosphorus, magnesium, sodium, potassium, sulfur, and chloride. They are needed to build muscles, blood, nerve cells, teeth, and bones. They are also essential electrolytes that the body requires to regulate blood volume and acid-base balance.

Unlike the major minerals, trace minerals are needed only in tiny amounts. Even though they can be found in the body in exceedingly small amounts, they are also very important to the human body. These minerals participate in most chemical reactions in the body. They are also needed to manufacture important hormones. The following are classified as trace minerals: iron, zinc, iodine, copper, manganese, fluoride, chromium, selenium, molybdenum, and boron.

Many vitamins (such as vitamins A, C, and E) and minerals (such as zinc, copper, selenium, or manganese) act as antioxidants. They protect the body against the damaging effects of free radicals. They scavenge or mop up these highly reactive radicals and change them into inactive, less harmful compounds. In so doing, these essential nutrients help prevent cancer and many other degenerative diseases, such as premature aging, heart disease, autoimmune diseases, arthritis, cataracts, Alzheimer's disease, and diabetes mellitus.

Water helps to regulate body temperature, transports nutrients to cells, and rids the body of waste materials.

Description

The four basic food groups, as outlined by the United States Department of Agriculture (USDA) are:

• dairy products (such as milk and cheese)
• meat and eggs (such as fish, poultry, pork, beef, and eggs)
• grains (such as bread cereals, rice, and pasta)
• fruits and vegetables

The USDA recommendation for adults is that consumption of meat, eggs, and dairy products should not exceed 20% of total daily caloric intake. The rest (80%) should be devoted to vegetables, fruits, and grains. For children age two or older, 55% of their caloric intake should be in the form of carbohydrates, 30% from fat, and 15% from proteins. In addition, saturated fat intake should not exceed 10% of total caloric intake. This lowfat, high-fiber diet is believed to promote health and help prevent many diseases, including heart disease, obesity, and cancer.

Allergenic and highly processed foods should be avoided. Highly processed foods do not contain significant amounts of essential trace minerals. Furthermore, they contain lots of fat and sugar as well as preservatives, artificial sweeteners and other additives. High consumption of these foods causes build up of these unwanted chemicals in the body and should be avoided. Food allergy causes a variety of symptoms including food cravings, weight gain, bloating, water retention. It may also worsen chronic inflammatory conditions such as arthritis.

— Mai Tran

Dictionary: nu·tri·tion   (nū-trĭsh'ən, nyū-)

Top

1. The process of nourishing or being nourished, especially the process by which a living organism assimilates food and uses it for growth and for replacement of tissues.
2. The science or study that deals with food and nourishment, especially in humans.
3. A source of nourishment; food.

[Middle English nutricion, from Old French nutrition, from Late Latin nūtrītiō, nūtrītiōn-, from Latin nūtrītus, past participle of nūtrīre, to suckle.]

The science of nourishment, including the study of the nutrients that each organism must obtain from its environment to maintain life and health and to reproduce. Although each kind of organism has its distinctive needs, which can be studied separately, a far-reaching biochemical unity in nature has been discovered which gives vastly more coherence to the whole subject. Many nutrients, such as amino acids, minerals, and vitamins, needed by higher organisms may also be needed by the lowest forms of life—single-celled bacteria and protozoa. The recognition of this fact has made possible highly important developments in biochemistry.

Mammals need for their nutrition (aside from water and oxygen) a highly complex mixture of more than 40 chemical substances, including amino acids; carbohydrates; certain lipids; fibers; a great variety of minerals, including several which are required only in minute amounts, commonly referred to as trace minerals; and vitamins. See also Amino acids; Carbohydrate metabolism; Lipid metabolism; Protein metabolism; Vitamin.

Early workers in human nutrition focused on the minimum amounts needed to prevent or cure acute deficiency diseases, such as scurvy and beriberi. Since that time, the Recommended Dietary Allowances (RDAs) in the United States and similar recommendations in other countries include consideration of biochemical criteria of adequacy. They also include approximate adjustments for age, sex, and pregnancy and lactation, along with a rough estimate for some other sources of individual variation. However, statistical data needed to adequately assess individual variations are not yet available for any nutrient.

Interests have shifted toward what may be more nearly optimal nutritional intakes, based on the amounts needed to promote health (not merely to avoid disease or biochemical deficiency), longevity, and resistance to chronic disorders, including cardiovascular disease, cancer, hypertension, and diabetes.

For modern humans, the problems of suboptimal nutrition have increased with the advent and extensive consumption of technologically derived, refined foods. These nonwhole “foods” have lost most or all of the nutrients present in the whole foods from which they derive. Modern dietary guidelines and nutrition education focus substantially on partially replacing nonwhole foods with whole grains, legumes, low-fat meats and dairy products, fish, vegetables, fruits, and nuts that retain their natural biochemical unity.

One of the bases for interest in nutrition is the fact that individuals who have differing genetic backgrounds have differing nutritional needs; for this reason, various human ills may arise because the individuals concerned do not get all of the nutrients in amounts compatible with their own distinctive requirements.

It is clear that improper nutrition may produce or contribute to almost every conceivable type of illness. Nutritional and medical research is yielding important advances in using improved nutrition to prevent, cure, and ameliorate disease and illness. See also Disease; Malnutrition; Metabolic disorders.

The origin of the term nutrition, and of ‘nutrients’, refers to all substances necessary for growth and for the maintenance of life and health of the body tissues. In this sense, not only food but also water and oxygen can be called nutrients, and their provision can be called nutrition. But in common usage, nutrition means provision of substances in food and drinks. These include the ‘fuels’ for metabolic energy production and the raw materials necessary for growth, repair, and maintenance of the body's fabric — carbohydrates, proteins and fats — and also the vitamins and minerals essential for these processes.

— Stuart Judge

See diets; food.

The process by which living organisms take in and use food for the maintenance of life, growth, the functioning of organs and tissues; the branch of science that studies these processes.

noun

Something fit to be eaten: aliment, bread, comestible, diet, edible, esculent, fare, food, foodstuff, meat, nourishment, nurture, nutriment, pabulum, pap, provender, provision (used in plural), sustenance, victual. Slang chow, eats, grub. See ingestion.

Definition: food
Antonyms: deprivation, starvation

The process of assimilation and use of essential food elements from the diet (for example, carbohydrates, fats, proteins, vitamins, mineral elements).

Definition

Good nutrition can help prevent disease and promote health. There are six categories of nutrients that the body needs to acquire from food: protein, carbohydrates, fat, fibers, vitamins and minerals, and water.

Proteins

Protein supplies amino acids to build and maintain healthy body tissue. There are 20 amino acids considered essential because the body must have all of them in the right amounts to function properly. Twelve of these are manufactured in the body but the other eight amino acids must be provided by the diet. Foods from animal sources

such as milk or eggs often contain all these essential amino acids while a variety of plant products must be taken together to provide all these necessary protein components.

Fat

Fat supplies energy and transports nutrients. There are two families of fatty acids considered essential for the body: the omega-3 and omega-6 fatty acids. Essential fatty acids are required by the body to function normally. They can be obtained from canola oil, flaxseed oil, cold-water fish, or fish oil, all of which contain omega-3 fatty acids, and primrose or black currant seed oil, which contain omega-6 fatty acids. The American diet often contains an excess of omega-6 fatty acids and insufficient amounts of omega-3 fats. Increased consumption of omega-3 oils is recommended to help reduce risk of cardiovascular diseases and cancer and alleviate symptoms of rheumatoid arthritis, premenstrual syndrome, dermatitis, and inflammatory bowel disease.

Carbohydrates

Carbohydrates are the body's main source of energy and should be a major part of total daily caloric intake. There are two types of carbohydrates: simple carbohydrates (such as sugar or honey) or complex carbohydrates (such as grains, beans, peas, or potatoes). Complex carbohydrates are preferred because these foods are more nutritious yet have fewer calories per gram compared to fat and cause fewer problems with overeating than fat or sugar. Complex carbohydrates also are preferred over simple carbohydrates for diabetics because they allow better blood glucose control.

Fiber

Fiber is the material that gives plant texture and support. Although it is primarily made up of carbohydrates, it does not have a lot of calories and usually is not broken down by the body for energy. Dietary fiber is found in plant foods such as fruits, vegetables, legumes, nuts, and whole grains.

There are two types of fiber: soluble and insoluble. Insoluble fiber, as the name implies, does not dissolve in water because it contains a high amount of cellulose. Insoluble fiber can be found in the bran of grains, the pulp of fruit and the skin of vegetables. Soluble fiber is the type of fiber that dissolves in water. It can be found in a variety of fruits and vegetables such as apples, oatmeal and oat bran, rye flour, and dried beans.

Although they share some common characteristics such as being partially digested in the stomach and intestines and have few calories, each type of fiber has its own specific health benefits. Insoluble fiber speeds up the transit of foods through the digestive system and adds bulk to the stools, therefore, it is the type of fiber that helps treat constipation or diarrhea and helps prevent colon cancer. On the other hand, only soluble fiber can lower blood cholesterol levels. This type of fiber works by attaching itself to the cholesterol so that it can be eliminated from the body, preventing cholesterol from re-circulating and being reabsorbed into the bloodstream.

Vitamins and Minerals

Vitamins are organic substances present in food and required by the body in a minute amount for regulation of metabolism and maintenance of normal growth and functioning. The most commonly known vitamins are A, B₁ (thiamine), B₂ (riboflavin), B₃ (niacin), B₅ (pantothenic acid), B₆ (pyridoxine), B₇ (biotin), B₉ (folic acid), B₁₂ (cobalamin), C (ascorbic acid), D, E, and K. The B and C vitamins are water-soluble, excess amounts of which are excreted in the urine. The A, D, E, and K vitamins are fat-soluble and will be stored in the body fat.

Minerals are vital to our existence because they are the building blocks that make up muscles, tissues, and bones. They also are important components of many life-supporting systems, such as hormones, oxygen transport, and enzyme systems.

There are two kinds of minerals: the major (or macro) minerals and the trace minerals. Major minerals are the minerals that the body needs in large amounts. The following minerals are classified as major: calcium, phosphorus, magnesium, sodium, potassium, sulfur, and chloride. They are needed to build muscles, blood, nerve cells, teeth, and bones. They also are essential electrolytes that the body requires to regulate blood volume and acid-base balance.

Unlike the major minerals, trace minerals are needed only in tiny amounts. Even though they can be found in the body in exceedingly small amounts, they are also very important to the human body. These minerals participate in most chemical reactions in the body. They also are needed to manufacture important hormones. The following are classified as trace minerals: iron, zinc, iodine, copper, manganese, fluoride, chromium, selenium, molybdenum, and boron.

Many vitamins (such as vitamins A, C, and E) and minerals (such as zinc, copper, selenium, or manganese) act as antioxidants. They protect the body against the damaging effects of free radicals. They scavenge or mop up these highly reactive radicals and change them into inactive, less harmful compounds. In so doing, these essential nutrients have been claimed to help prevent cancer and many degenerative diseases, such as premature aging, heart disease, autoimmune diseases, arthritis, cataracts, Alzheimer's disease, and diabetes mellitus.

Water

Water helps to regulate body temperature, transport nutrients to cells, and rid the body of waste materials.

Origins

Unlike plants, human beings cannot manufacture most of the nutrients they need to function. They must eat plants and/or other animals. Although nutritional therapy came to the forefront of the public's awareness in the late Twentieth century, the notion that food affects health is not new. John Harvey Kellogg was an early health food pioneer and an advocate of a highfiber diet. An avowed vegetarian, he believed that meat products were particularly detrimental to the colon. In the 1870s, Kellogg founded the Battle Creek Sanitarium, where he developed a diet based on nut and vegetable products.

Benefits

Good nutrition helps individuals achieve general health and well-being. In addition, dietary modifications might be prescribed for a variety of complaints including allergies, anemia, arthritis, colds, depression, fatigue, gastrointestinal disorders, high or low blood pressure, insomnia, headaches, obesity, pregnancy, premenstrual syndrome (PMS), respiratory conditions, and stress.

Nutritional therapy also may be involved as a complement to the allopathic treatments of cancer, diabetes, and Parkinson's disease. Other specific dietary measures include the elimination of food additives for attention deficit hyperactivity disorder (ADHD), gluten-freediets for schizophrenia, and dairy-free diets for chronic respiratory diseases.

A high-fiber diet helps prevent or treat the following health conditions:

• High cholesterol levels. Fiber effectively lowers blood cholesterol levels. It appears that soluble fiber binds to cholesterol and moves it down the digestive tract so that it can be excreted from the body. This prevents the cholesterol from being reabsorbed into the bloodstream.
• Constipation. A high-fiber diet is the preferred nondrug treatment for constipation. Fiber in the diet adds more bulk to the stools, making them softer and shortening the time foods stay in the digestive tract.
• Hemorrhoids. Fiber in the diet adds more bulk and softens the stool, thus reducing painful hemorrhoidal symptoms.
• Diabetes. Soluble fiber in the diet slows down the rise of blood sugar levels following a meal and helps control diabetes.
• Obesity. Dietary fiber makes a person feel full faster.
• Cancer. Insoluble fiber in the diet speeds up the movement of the stools through the gastrointestinal tract. The faster food travels through the digestive tract, the less time there is for potential cancer-causing substances to work. Therefore, diets high in insoluble fiber help prevent the accumulation of toxic substances that cause cancer of the colon. New studies released in 2003 seemed to confirm these findings. Because fiber reduces fat absorption in the digestive tract, it also may prevent breast cancer.

A diet low in fat also promotes good health and prevents many diseases. Low-fat diets can help treat or control the following conditions:

• Obesity. High fat consumption often leads to excess caloric and fat intake, which increases body fat.
• Coronary artery disease. High consumption of saturated fats is associated with coronary artery disease.
• Diabetes. People who are overweight tend to develop or worsen existing diabetic conditions due to decreased insulin sensitivity.
• Breast cancer. A high dietary consumption of fat is associated with an increased risk of breast cancer.

Description

The four basic food groups, as outlined by the United States Department of Agriculture (USDA) are:

• dairy products (such as milk and cheese)
• meat and eggs (such as fish, poultry, pork, beef, and eggs)
• grains (such as bread, cereals, rice, and pasta)
• fruits and vegetables

The USDA recommendation for adults is that consumption of meat, eggs, and dairy products should not exceed 20% of total daily caloric intake. The rest (80%) should be devoted to vegetables, fruits, and grains. For children age two or older, 55% of their caloric intake should be in the form of carbohydrates, 30% from fat, and 15% from proteins. In addition, saturated fat intake should not exceed 10% of total caloric intake. This low-fat, highfiber diet is believed to promote health and help prevent many diseases, including heart disease, obesity, and cancer.

Allergenic and highly processed foods should be avoided. Highly processed foods do not contain significant amounts of essential trace minerals. Furthermore, they contain lots of fat and sugar as well as preservatives, artificial sweeteners and other additives. High consumption of these foods causes buildup of these unwanted chemicals in the body and should be avoided. Food allergy causes a variety of symptoms including food cravings, weight gain, bloating, and water retention. It also may worsen chronic inflammatory conditions such as arthritis.

Preparations

An enormous body of research exists in the field of nutrition. Mainstream Western medical practitioners point to studies that show that a balanced diet, based on the USDA Food Guide Pyramid, provides all of the necessary nutrients. However, the USDA is working to revise the pyramid for the first time in a decade. Other pyramids are suggested by various research agencies, many of which emphasize different nutrition areas. A Harvard University researcher emphasizes whole grains and plant oils over meat, dairy and refined carbohydrates. Some nutritionists believe that the USDA will modify the Food Pyramid to reflect similar modifications. The basic pyramid will likely not change, but explanations about the types of fats, grains and carbohydrates that are best to choose are likely.

In the first revision of the Food Guide Pyramid in 2003, the USDA proposed new patterns about how much Americans eat. Calorie recommendations and vitamin intake will be based on a person's age, sex, and activity level. The complete revision was proposed for final publishing in the winter of 2005. As of early 2004, the Food Guide Pyramid recommends the following daily servings in six categories:

• grains: Six or more servings
• vegetables: Five servings
• fruits: Two to four servings
• meat: Two to three servings
• dairy: Two to three servings
• fats and oils: Use sparingly

A new food guide pyramid for various vegetarian diets has been released by the American Dietetic Association (ADA). The guide helps vegetarians obtain the vitamins and minerals they need from whole grains, vegetables, fruits, legumes, nuts and other protein-rich foods.

Precautions

Individuals should not change their diets without the advice of nutritional experts or health care professionals. Certain individuals, especially children, pregnant and lactating women, and chronically ill patients should only change their diets under professional supervision.

Side Effects

It is best to obtain vitamins and minerals through food sources. Excessive intake of vitamins and mineral supplements can cause serious physiological problems. 2001 guidelines to help nutritionists counsel cancer patients in use of complementary and alternative medicine reported that 73% of cancer patients used these therapies in addition to their allopathic treatment. Of those, only about 38% discussed the alternative therapies with their physicians. Patients using dietary supplements should document their use, discuss them with their doctor or nutritionist, and watch standard cautions like possible interactions with prescribed drugs, cumulative effects of several supplements containing the same vitamin or mineral, and to stop taking the supplements if adverse reactions occur.

The following is a list of possible side effects resulting from excessive doses of vitamins and minerals:

• vitamin A: Birth defects, irreversible bone and liver damage
• vitamin B₁: Deficiencies in B₂ and B₆
• vitamin B₆: Damage to the nervous system
• vitamin C: Effects on the absorption of copper; diarrhea
• vitamin D: Hypercalcemia (abnormally high concentration of calcium in the blood)
• phosphorus: affects the absorption of calcium
• zinc: affects absorption of copper and iron; suppression of the immune system

Research & General Acceptance

Due to a large volume of scientific evidence demonstrating the benefits of the low-fat, high-fiber diet in disease prevention and treatment, this diet has been accepted and advocated by both complementary and allopathic practitioners.

Resources

Books

Bruce, Debra Fulghum, and Harris H. McIlwain. The Unofficial Guide to Alternative Medicine. New York: Macmillan, 1998.

Cassileth, Barrie R. The Alternative Medicine Handbook. New York: W.W. Norton, 1998.

Credit, Larry P., Sharon G. Hartunian, and Margaret J. Nowak. Your Guide to Complementary Medicine. Garden City Park, New York: Avery Publishing Group, 1998.

U.S. Preventive Services Task Force Guidelines. "Counseling to Promote a Healthy Diet." Guide to Clinical Preventive Services, 2nd edition.http://cpmcnet.columbia.edu/texts/gcps/gcps0066.html.

Winick, Myron. The Fiber Prescription. New York: Random House, Inc., 1992.

Periodicals

Halbert, Steven C. "Diet and Nutrition in Primary Care: From Antioxidants to Zinc." Primary Care: Clinics in Office Practice (December 1997): 825-843.

Mangels, Reed. "New Vegetarian Food Guide." Vegetarian Journal (July–August 2003): 12.

Shapiro, Alice C., et al. "Guidelines for Responsible Nutrition Counseling on Complementary and Alternative Medicine." Nutrition Today (November-December 2001): 291 -297.

Sugarman, Carole. "USDA Proposes New Intake Patterns for Food Guide Pyramid." Food Chemical News (Sept. 15, 2003): 1.

Turner, Lisa. "Good 'n Plenty." Vegetarian Times (February 1999):48 "Two Studies Find High-fiber Diet Lowers Colon Cancer Risk." Ca (July–August 2003): 201.

VanBeusekom, Mary. "Converted Food Pyramid: the USDA Revises its Decade-old Food Guidelines." MPLS-St. Paul Magazine (August 2003): 60–64.

Vickers, Andrew, and Catherine Zollman. "Unconventional approaches to nutritional medicine." British Medical Journal (November 27, 1999): 1419.

Organizations

American Association of Nutritional Consultants. 810 S. Buffalo Street, Warsaw, IN 46580. (888) 828-2262.

American Dietetic Association. 216 W.Jackson boulevard, Suite 800, Chicago, IL 60606-6995. (800) 366-1655. http://www.eatright.org/.

[Article by: Teresa G. Odle]

Definition

The process by which humans take in and use food in their bodies; also the study of diet as it relates to health.

Description

Good nutrition in childhood lays the foundation for good health throughout a person's lifetime. With the proliferation of fast food restaurants, the number of junk food commercials on television, and the increased trend toward eating out, it is more difficult than ever for parents to ensure that their children maintain a nutritious diet. Across the last decades of the twentieth century, increasing affluence and the widespread availability of vitamin-enriched foods have shifted the focus of nutritional concerns in the United States from obtaining minimum requirements to cutting down on harmful elements in one's diet. Parents need to be as concerned about high levels of fat, cholesterol, sugar, and salt, as well as adequate intake of vitamins, minerals, and other nutrients.

The American Academy of Pediatrics, the National Academy of Sciences, the American Heart Association, and other health-care organizations agree that fat should not account for more than 30 percent of the calorie intake of children over the age of two, and saturated fat should account for under 10 percent. The main dietary sources in children's diets of saturated fat are whole milk, cheese, hot dogs, and luncheon meats. Recommendations for dietary change include switching to 1 percent or skim milk, low-fat cheese, and meats from which the fat can be trimmed. Since fat is important for growth, experts also caution that fat intake should not be under 25 percent of daily calorie intake and that parents of children under age two should not restrict fat in their diets.

The amount of refined sugar in children's diets—typically accounting for 14 percent of calorie intake by adolescence—is another cause for concern. Although sugar is known to cause tooth decay and also may be associated with behavior problems, the greatest danger in consuming foods high in added sugar is that these "empty calories" may replace the more nutritious foods that children need in order to maintain good health. (Soft drinks, perhaps the single greatest source of refined sugar in the diet of children and teenagers, get virtually all their calories from sugar and offer no nutrients.) This high intake of fat can lead to excess weight and, potentially, obesity.

Another element that needs to be restricted in children's diets is the intake of sodium through salted foods. Sodium has been closely linked to hypertension (high blood pressure), which increases a person's risk of heart disease and stroke. It has been determined that 18-year-olds need only 500 milligrams of sodium daily. In addition to limiting the amounts of fat, cholesterol, salt, and sugar in their children's diets, health authorities also recommend that parents concerned about nutrition ensure that children obtain a generous supply of complex carbohydrates (found in such foods as beans, potatoes, whole-grain products, and pasta) and have at least five servings of fresh fruits and vegetables daily.

Infancy

The first nutritional decision that must be made for a child by a parent or primary caregiver is whether to breastfeed or bottle feed. Breast milk is generally considered the best food for an infant up to the age of six to nine months. It has virtually all the nutrients that babies need and in the right balance. In addition, it contains important antibodies that help protect infants from infection at a time when their own immune systems are not yet fully developed.

The composition of breast milk actually changes during the first two weeks after a baby is born. Initially, it consists largely of colostrum, a substance that has more protein than complete breast milk and lower amounts of fat and sugar. It is also rich in the antibody immunoglobin A, which helps protect against infections. By the tenth day after birth, the regular breast milk, containing more carbohydrates and fat and less protein, is produced. The amounts of carbohydrates and fat gradually continue to increase, as will the quantity of the milk itself, to match the needs of the growing baby. Although most full-term infants get all the necessary nutrients from breastfeeding, some may need supplements of vitamins D and K.

Women who are either unable to breastfeed or who choose not to do so usually feed their babies formula made from processed cow's milk, generally reconstituted skim milk with vegetable oils added to substitute for the missing butterfat, which is difficult for infants to digest. Lactose (milk sugar) is also added, and some formulas contain whey protein as well. For infants who demonstrate sensitivity to cow's milk, formulas based on soy protein are available.

Breast milk or formula provides all the nutrients an infant needs up to the age of four to six months. Contrary to past beliefs, it has been found that not only do babies not need solid foods before then, introducing solids too early may lead to food allergies or overfeeding. Regular grocery-store cow's milk, which cannot be adequately digested by infants and can cause gastrointestinal bleeding, should not be introduced until a child is a year old. As the first solid food, pediatricians often recommend cereal made from a grain other than wheat, such as rice. The first solid foods may be either commercial baby food or strained foods prepared at home. Once solid foods have been introduced, infants still need to receive most of their nourishment from either breast milk or formula during their first year.

Toddlerhood

During children's second year, their growth rate slows dramatically compared to the prior period. In the first year, their birth weight triples, their length increases by 50 percent, and the size of their brain doubles. After that first year, it takes several years for their weight to even double. They will grow in spurts, with each spurt followed by a period of weight gain. This decreased growth leads to a decreased demand for food, often manifested in a newfound pickiness. As long as a child consumes an adequate, varied diet over a period of several days, parents are cautioned against becoming unduly concerned over a single day of unbalanced eating. Toddlers need to eat more than three times a day, either five or six small meals or three major ones with snacks in between.

Preschool

Preschoolers are still growing relatively slowly. Their weight increases about 12 percent between the ages of three and five, although their appearance changes considerably as they lose the baby fat of infancy and toddlerhood. They are still picky eaters, generally eating less—and less consistently—than their parents would like. Although their fat requirement is not as high as that of infants, preschoolers still require more fat and fewer carbohydrates than adults. Fat is needed both for growth and for regulation of body temperature. Also, preschoolers need more than twice as much protein as adults. If the nutritional recommendations of the National Academy of Sciences are followed, a preschooler's diet will consist of 40 percent carbohydrates, 35 percent fats, 20 percent protein, and 5 percent fiber.

Between the ages of three and five, children's tastes expand considerably, and they are willing to consider foods they would have refused as toddlers. Four-year-olds can generally eat whatever foods the rest of the family is having. Preschoolers still cannot eat enough at three meals to meet their nutritional needs, and nutritious snacks are important. By this age, children's food choices can be strongly influenced by others. They will imitate good eating habits they see practiced by their parents, but they can also be easily swayed by television commercials for junk food.

School Age

The diet of young school-age children, like that of preschoolers, should contain, in order of importance, carbohydrates, fat, and protein. A recommended proportion of these nutrients is 55 percent of the daily calorie intake from carbohydrates, 30 percent from fats, and 15 percent from protein. Once children begin spending a full day in school, a substantial, nutritious breakfast becomes more important than ever. Breakfast has been shown to affect the concentration and performance of elementary school children. Ideally, a balanced breakfast for a school-age child contains food high in protein as well as fruit and bread or another form of grain.

A major change affecting the nutrition of school-age children is the growth of opportunities to eat outside the home. The carefully packed homemade lunch may be traded for a salty snack or cupcake, and parts of it may be discarded. Vending machines and stores offer more temptations. In addition, school lunch programs differ widely in quality; even the nutritional value of a single food, such as a hamburger, can vary significantly depending on how it is prepared and what ingredients are used.

Adolescence brings its own set of nutritional needs and challenges. Beginning with the pre-teen years, children undergo their most intensive period of physical growth since infancy and need more food than at any other stage of life, particularly if they participate in sports. Teenagers, especially boys, are notorious for being able to empty the refrigerator of food, usually without gaining excess weight. Early adolescence in particular is a time of increased nutritional requirements for girls, who experience their greatest growth spurt at this time and also begin menstruating. It is difficult for weight-conscious teenage girls to eat enough to satisfy their minimum daily iron requirement of 18 milligrams, and they should try to eat either foods that are naturally rich in iron, such as turkey, beef, liver, and beans, or foods made from iron-enriched cereals. Adequate calcium intake is essential for the rapidly growing bones of teenagers, but milk has often been replaced by soft drinks as the beverage of choice among this age group. Parents should encourage adolescents, especially girls, to eat other foods rich in calcium, such as cheese, salmon, and broccoli.

As adolescents grow more independent, the number of meals and snacks eaten away from home increases as they spend more time with friends and take increased responsibility for arranging their own meals, with fast foods, soft drinks, and sweets often prominent on the menu. In addition to the natural appeal of these foods, peer pressure contributes to the choice of a diet soft drink over milk or juice, or pizza over broccoli. Although parents cannot control the eating habits of their teenagers, they can influence them by consistently making nutritious foods available at home and, at least in some cases, by discussing the benefits of good nutrition with them, especially if a relative or friend has had an illness, such as heart disease or colon cancer, that has known links to diet.

Common Problems

A special problem that may affect childhood nutrition is the presence of food allergies, which are more common in children than in adults. They are most likely to begin when a child is very young and the immune system is still sensitive, usually in infancy. Food allergies also tend to run in families: if one parent has food allergies, a child has a 40 percent likelihood of developing one. This figure rises to 75 percent if both parents have food allergies. Common symptoms of food allergies include hives and rashes; swelling of the eyes, lips, and mouth; respiratory symptoms; and digestive problems. Foods that most often produce allergic reactions in infants are cow's milk, soy products, and citrus fruits. Other common childhood allergens include wheat, nuts, chocolate, strawberries, tomatoes, corn, and seafood. In time, childhood food allergies are often outgrown. Feeding a child with food allergies is a challenging but not impossible task for parents. A variety of foods can be substituted for those to which a child is allergic: soy products for milk and other dairy products; carob for chocolate; and, in the case of wheat allergies, products or flour made from grains such as rice or oats.

Parental Concerns

Vegetarian Kids

About 2 percent of Americans ages six to 17 (about 1 million) are vegetarian, the same percentage as among American adults, and 0.5 percent are vegan, according to a 2002 survey by the Vegetarian Resource Group (VRG). Six percent of six- to 17-year-olds do not eat meat but eat fish and/or poultry. Teens who follow a vegetarian diet are more likely to meet recommendations for total fat, saturated fat, and number of servings of fruits and vegetables as compared to non-vegetarians. They also have higher intakes of iron, vitamin A, fiber, and diet soda, and lower intakes of vitamin B12, cholesterol, and fast food. Most teens, whether they are vegetarian or not, do not meet recommendations for calcium, according to the VRG survey. The study concluded that rather than viewing adolescent vegetarianism as a phase or fad, the diet could be viewed as a healthy alternative to the traditional American meat-based diet. The study also said that vegetarian diets in adolescence could lead to lifelong health-promoting dietary practices. The study was reported in the July-August 2002 issue of the VRG publication Vegetarian Journal.

Parents should closely monitor their vegetarian child's height, weight, and general health. A child who is not getting enough vitamins and nutrients may have symptoms such as skin rashes, fatigue, a painful and swollen tongue, irritability, pale skin, mental slowness, or difficulty breathing. The diets of vegetarian adolescents should be monitored closely to make sure they include a variety of foods, including fruits, vegetables, beans, whole grains, and non-meat protein sources. For vegetarians who do not eat fish, getting enough omega-3 essential fatty acids may be an issue, and supplements such as flax-seed oil should be considered, as well as walnuts and canola oil. Another essential fatty acid, omega-6, found in fish, can be obtained from borage oil or evening primrose oil supplements.

When to Call the Doctor

Parents should consult their child's pediatrician or physician if they are unsure the child's diet is nutritionally adequate. A doctor should also be consulted if a child's weight or height is not appropriate for their age.

Resources

Books

Evers, Connie Liakos. How to Teach Nutrition to Kids. Portland, OR: 24 Carrot Press, 2003.

Salmon, Margaret Belais. Food Facts for Teenagers: A Guide to Good Nutrition for Teens and Preteens. Springfield, IL: Charles C. Thomas Publisher Ltd., 2002.

Schlosser, Eric. Fast Food Nation: The Dark Side of the All-American Meal. Wilmington, MA: Houghton Mifflin Company Trade & Reference Division, 2001.

Shield, Jodie, and Mary Catherine Mullen. The American Dietetic Association Guide to Healthy Eating for Kids: How Your Children Can Eat Smart from Five to Twelve. Hoboken, NJ: Wiley, 2002.

Periodicals

Feskanich, Diane, et al. "Modifying the Healthy Eating Index to Assess Diet Quality in Children and Adolescents" 104 Journal of the American Dietetic Association (September 2004): 1375–83.

Mangels, Reed. "Good News about Vegetarian Diets for Teens" Vegetarian Journal (July-August 2002): 20–1.

Nicklas, Theresa A., et al. "Children's Meal Patterns Have Changed Over 21-Year Period: The Bogalusa Heart Study" 104 Journal of the American Dietetic Association (May 2004): 753–61.

Nicklas, Theresa A., et al. "The Importance of Breakfast Consumption to Nutrition of Children, Adolescents, and Young Adults" Nutrition Today 39 (January-February 2004): 30–9.

Onderko, Patty. "The (Not So) Great American Baby Diet: A New Study Sheds Light on What Our Babies and Toddlers are Eating Today—And How You Can Improve Their Diet for Tomorrow" Baby Talk 69 (February 1, 2004): 45.

Organizations

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606–6995. Web site: www.eatright.org.

International Food Information Council. 1100 Connecticut Ave. NW, Suite 430, Washington, DC 20036. Web site: www.ific.org.

Web Sites

"Children's Nutrition Guide." Available online at www.keepkidshealthy.com/nutrition (accessed November 12, 2004).

"Kids Nutrition." Baylor College of Medicine. Available online at www.kidsnutrition.org/ (accessed November 12, 2004).

[Article by: Ken R. Wells]

Few subjects are more important to public health than food. One of the major ways in which humans interact with their environment is through our food. The science of nutrition has developed through the study of the components of foods that are required to sustain life and to maintain health. Improper diet can cause disease if important nutrients are missing from the diet, and inappropriate dietary practices can increase the risk of certain diseases.

Essential nutrients are substances that must be in the human diet to support life. These essential nutrients include vitamins, inorganic elements, essential amino acids, essential fatty acids, and a source of energy, and water. A lack of a nutrient or an insufficient amount of a nutrient can result in a deficiency disease that can be life threatening in extreme cases. The essential nutrients are widely distributed in foods and most people can obtain sufficient amounts of them if they consume a varied diet.

Elements of Human Nutrition

Energy. Most of the food consumed is used by the body to supply energy. The body is able to digest and absorb into the blood stream components of carbohydrates, fats, and protein that can be metabolized by the body to release energy. Energy is used to maintain body temperature, support metabolic processes, and to support physical activity. People are generally in a state of energy balance, that is, they consume as much energy as they use to support their bodies and daily living. They tend to gain weight if they are in positive energy balance, or lose weight if they take in less than they expend. Most excess energy is stored by the body as fat. Energy needs are usually expressed in kilocalories, but in much of the world's scientific literature, energy expenditure is expressed in joules or kilojoules (1 kilocalorie equals 4.184 kilojoules).

The energy expended by the body when at rest is quite constant between individuals and can be

Table 1

estimated quite closely by prediction equations that take into account age, sex, and body weight. The resting metabolic weight of a 70-kilogram (154-lb.) man, for example, is estimated to be 1750 kilocalories per day, and for a 58-kilogram (128-lb.) woman, 1350 kilocalories per day. The total daily energy needs are related to the amount of physical activity expended in the course of everyday life. A person whose life style involves light amounts of activity may have a total energy expenditure of about one and one-half times their resting metabolic rate, while a person who is engaged in very intense physical activity may expend over twice as much energy as their resting metabolic rate in the course of twenty-four hours. Exercise can increase the metabolic rate considerably, depending on the type and duration of the activity. The amount of energy expended by certain types of physical activity is shown in Table 1.

Protein. The principal structural components of body soft tissues are proteins, which are made by the body from amino acids. The amino acids along with the nucleic acids are the principle nitrogen-containing components of the body and of most foods. The enzymes that regulate most body processes are also proteins. The body can synthesize many of the amino acids needed for protein syntheses, but some amino acids must be obtained from the proteins in the diet. The dietary essential amino acids for humans are threonine, valine, leucine, isoleucine, methionine, lysine, histidine, and tryptophan. Two others can only be formed from essential amino acids: tryosine from phenylalanine, and cystine from methionine. Human dietary protein requirements are quite modest. An adult man of average weight is estimated to need about sixty-three grams of protein per day, while an average woman is estimated to need about fifty grams. The protein must supply the essential amino acids required by humans and sufficient total nitrogen to allow syntheses of the other amino acids required for protein synthesis.

Fats. Fats are synthesized from carbohydrates, but the body is unable to make certain fatty acids, which are components of fats. These essential fatty acids, notably linoleic and linolenic acid, must be supplied by dietary fats. Fats that are solid at room temperature, such as butter or lard, usually contain high amounts of saturated fatty acids such as palmitic or stearic acid. Fats that are liquid at room temperature such as vegetable oils are higher in unsaturated fatty acids, which include oleic acid as well as the linoleic and linolenic acid. Fat is the most concentrated source of energy available to humans, supplying about nine kilocalories per gram of dietary fat, compared to four kilocalories per gram of carbohydrate and protein. Fat is also the principal storage form of energy in the body.

Vitamins. Vitamins are a diverse group of dietary essentials that have important functions in the body. The vitamins known to be required by humans are listed in Table 2. Many of them are components of co-enzymes, molecules that are required for some enzymes to carry out certain metabolic processes. Others, such as vitamin E and vitamin C, act as antioxidants, protecting body components from damage from oxygen needed by the body for metabolism. Some are more like hormones, such as vitamin D, which regulates the absorption of calcium from the intestine and the formation of bones. Vitamin D can actually be formed by the action of ultraviolet light from the sun on vitamin D precursors found in the skin, but since this synthesis may not be sufficient at times, humans need a dietary source of vitamin D. Vitamin A is a component of visual pigments in the eye that respond to light stimuli and are essential for sight.

A deficiency of a vitamin may result in a characteristic deficiency disease related to the body function affected by the lack of the vitamin. Vitamin D deficiency can cause soft bones in children, a condition called rickets; vitamin A deficiency

Table 2

may cause night blindness and even blindness in its more severe form. Many of the vitamins have multiple functions in the body, and deficiency diseases can be severely debilitating in severe cases. Vitamins are required in very small amounts by the body. Only a few micrograms of vitamin B₁₂is required each day, while vitamin C requirements may be from sixty to one hundred milligrams per day.

Inorganic elements. Humans also require several inorganic elements as components of the diet. The inorganic elements known to be required by humans are listed in Table 2. These elements may have a structural function, such as calcium and phosphorus, which are needed for bone synthesis, or they may have a catalytic function similar to some of the vitamins. They are required for the action of many enzymes in the body. Sodium and potassium are essential for fluid balance. Iodine is an essential component of thyroxin, the hormone produced by the thyroid gland. Some of the inorganic elements are required in extremely small quantities, only micrograms per day, while other elements may be needed in higher amounts. Soils vary in their content of some of the trace elements, and plants grown in some areas may be deficient in an essential element. This has been true for iodine, where a deficiency is still observed in many areas of the world, and selenium, where geographically based human deficiency disease has been observed.

Nutrition Recommendations

In the United States, the National Academy of Sciences, through the National Research Council and The Institute of Medicine, has convened expert groups since 1941 to establish nutrition recommendations to be used by individuals and institutions for planning nutritionally adequate diets. These groups have established recommended dietary allowances (RDAs) as the daily dietary intake level for a specific nutrient that is sufficient to meet the nutritional requirements of nearly all (97–98 percent) individuals in the life stage and gender group specified. In the most recent recommendations, dietary reference intakes (DRIs) have been specified that have attempted to estimate average nutrient requirements, RDAs, and an upper limit of safe nutrient intake. Where data are not sufficient to set a precise RDA, new recommendations called adequate intake (AI) define a recommendation for some nutrients.

The RDAs and AIs are used to plan diets for groups in hospitals, the military, large institutions, to set standards for government food programs such as school lunches, to establish nutritional labeling, and for counseling individuals. Similar dietary recommendations have been made by expert groups convened in many countries and also by international organizations such as the World Health Organization and the Food and Agricultural Organization of the United Nations. These recommendations are periodically revised to include information from most recent research findings. The latest recommendations for dietary reference intakes can be obtained in the United States from the National Academy Press, 2101 Constitution Avenue, NW, Washington, D.C. 20418.

Recommendations have been established for most nutrients where sufficient research data are available to make reliable estimates. The nutrient recommendations are given for different age groups and are differentiated by sexes because of different nutritional needs at different stages of life. Infants and young children who are growing rapidly have different nutrient needs compared to adults. Women who are menstruating need more iron to replace blood lost in the menstruation compared to postmenopausal women or men. Similarly, there are special needs for pregnant and lactating women. There is increasing evidence accumulating about the needs of the elderly, and nutrition recommendations now include a category for individuals over seventy years of age.

Recent revisions of nutrition recommendations have taken into account public health concerns about osteoporosis, a condition in which bone mineral is lost and older individuals become more vulnerable to bone fractures. New recommendations stress the importance of maintaining a high level (1200 mg/day) of calcium intake by both men and women over fifty years of age in an attempt to reduce loss of bone mineral. Similarly, recommendations for folic acid intake have also been revised to stress the importance of sufficient folic acid consumption by women who may become pregnant. Insufficient folic acid has been associated with a higher incidence of birth defects. The concern for adequate intake of folic acid led to the fortification of enriched grain products with folic acid in the United States beginning in 1998.

Nutrient recommendations also take into consideration the efficiency by which nutrients are digested and absorbed from foods. The form in which iron is ingested has a major influence on how much food iron is absorbed into the body. Iron in animal products is well absorbed because it is found as a component of hemoglobin or muscle pigments, while iron in plants, found as inorganic salts, is poorly absorbed. Some components of plants, such as phytic acid and tannins, also interfere with iron absorption. Therefore, dietary recommendations for iron intake must consider the availability of iron in the foods being consumed.

Public Health Issues

In the early part of the twentieth century, nutritional disorders were common. Pellagra, a disease caused by a deficiency of nicotinic acid, was widespread in the southern United States. Rickets, from vitamin D deficiency, was common, and goiters from iodine deficiency were widespread. Iron-deficiency anemia and riboflavin deficiency were frequently observed. In parts of Asia, beriberi, a disease caused by thiamin deficiency, was a public health problem. The discovery and characterization of the vitamins made it possible to produce them in large amounts, and the enrichment of grain products with niacin, riboflavin, thiamine, and iron largely eliminated B-vitamin deficiencies in the United States as a public health problem. Similarly, the addition of vitamins A and D to milk provided protection from deficiency of the nutrients. The use of iodized salt essentially eliminated goiter from the U.S. population.

Unfortunately, nutritional deficiencies have not been eliminated from much of the world even today. A combination of poor diet, poor sanitation, and lack of safe water leading to frequent intestinal infections, causes more than 200 million of the world's children to be shorter and weigh less than children in good environments at the same age. These malnourished children are often born underweight from mothers who are also underweight and of poor nutritional status. Measures of the degree of malnutrition that are frequently used include a comparison of a child's weight for age, height for age, and weight for height with norms established by similar measurements on a well-nourished population of children. A usual convention classifies a child whose weight for age is more than two standard deviations below the standard as malnourished, and those three standard deviations below the standard are usually considered severely malnourished. The most vulnerable time for growth faltering in children is the period from six months of age to two years, when breast feeding stops and weaning foods are introduced. A combination of poor weaning foods, exposure to contaminated water, and poor sanitation that results in frequent bouts of diarrhea and the occurrence of other childhood diseases contributes to the poor growth of children after weaning.

The United Nations estimates that more than two-hundred million of the world's children are stunted, with the largest numbers being found in South Asia and in Africa. Similarly, about 4 percent of the world's population is considered at risk for iodine deficiency disorders including goiter, cretinism, and mental retardation. Vitamin A deficiency is estimated to affect about 3.3 million children in the world. Iron deficiency anemia is also the most prevalent nutritional deficiency in the world. Over 90 percent of those effected live in developing countries. The United Nations has estimated that severe anemia is a contributing factor to 50 percent of maternal deaths in developing countries.

Nutritional deficiencies are common in the refugees displaced by wars and natural disasters. Assistance is provided by the United Nations High Commissioner for Refugees to more than 26 million people world wide, and there are other internally displaced people in the world that may number as many as 31 million. The difficulty of providing food for these displaced groups puts them at risk for nutritional deficiencies.

Nutritional deficiencies are rare in most industrialized nations in Europe, Asia, and the Americas, and among the higher income groups of the developing world. The public health issues related to nutrition in these nations are concerned with over–consumption of energy, inadequate levels of activity, and improper food choices. Dietary practices are known to be risk factors for severe chronic diseases, including hypertension, atherosclerotic cardiovascular disease, and several types of cancers. The amount and type of fats seem to influence the risk of atherosclerotic cardiovascular diseases and to risk of certain forms of cancer. The consumption of saturated fatty acids and trans fatty acids found in certain hydrogenated cooking fats increases the levels of serum total cholesterol and cholesterol associated with serum low density lipoproteins (LDL) and thus increases the risk of artheriosclerosis and coronary heart disease. Diets high in fruits, vegetables, legumes, and cereal products are associated with a lower occurrence of coronary heart disease and certain cancers.

Genetic variations occur among individuals in their response to food. Variations in various blood lipoprotein components can effect an individual's response to dietary fat and cholesterol, and risk of coronary heart disease. There appears to be a genetic component to susceptibility to obesity. As more information is known about the human genome, it may be possible to predict more accurately individual risks for disease, and the dietary factors that may modify this risk.

Obesity. Dietary patterns that are characterized by the consumption of energy-rich, high-fat foods are considered to be factors contributing to obesity, particularly when the high intake of energy is not accompanied by appropriate physical activity. Obesity in adults is defined by reference to the body mass index (BMI), a relationship that takes into account both height and body weight. The BMI is calculated as weight in kilograms/height in meters squared. In pounds and inches it is calculated by weight (pounds)/height (inches)²× 704.5. A person with a body mass index between 20 to 25 is considered in the normal range, while a body mass index of 25 to 30 is considered overweight, and over 30 is considered obese.

The prevalence of obesity in the United States has increased markedly in recent years. The prevalence of overweight children ages six to eleven in surveys conducted in the early 1970s was 6.5 percent of males and 4.9 percent for females. By 1988–1994, the prevalence of overweight in this age grouping had increased to 11.4 percent and9.9 percent for males and females respectively. On the basis of surveys carried out between the years 1988 and 1994, more than 50 percent of American adults were considered overweight on the basis of having a BMI greater than 25. In further surveys, 17.9 percent of U.S. adults were considered obese in 1988, compared with 12 percent in 1991. The increasing prevalence of obesity is of considerable public health concern as excess weight is associated with greater risk of mortality, non-insulin dependent Type II diabetes mellitus, hypertension, stroke, osteo-arthritis, and some cancers. The annual number of deaths attributed to obesity in the United States has been estimated at more than 280,000 persons.

The control of obesity is difficult, and weight reduction is difficult to maintain. The most effective weight loss schemes seem to be those that reduce weight slowly, from one-half to one pound per week, and that involve both reduction in energy intake and an increase in physical activity. For overweight individuals, a reduced intake of from 300 to 500 kilocalories per day should result in a loss of one-half to one pound per week, while severely obese individuals may need to reduce energy intake by 500 to 1000 kilocalories per day to achieve a one to two pound per week weight loss.

Table 3

Dietary guidelines. The concern for appropriate food choices have led many countries to issue dietary guidelines that provide advice that goes beyond the recommendations for individual nutrients covered by the recommended dietary allowances. The year 2000 dietary guidelines for Americans are shown in Table 3. These are issued by the U.S. Department of Agriculture and the U.S. Department of Health and Human Services and are revised about every five years. This publication represents the only official dietary advice to consumers by the U.S. Government. The full text of the bulletin provides more detailed advice on food choices. Many countries have published similar dietary guidelines to guide food choices to reduce the dietary risk factors associated with chronic disease.

To give advice to consumers regarding appropriate food choices to implement dietary guidelines, food guides have been developed. One of the most popular representations of a food guide is the dietary pyramid that has been published by the U.S. Department of Agriculture and the Department of Human Services. This food guide illustrates the importance of building a healthy diet on a base of cereal-based foods supplemented liberally with fruits and vegetables. Foods high in protein and fat should be consumed sparingly. The pyramid provides the number of recommended daily servings of the food groups.

Food supplies. The world population is projected to increase about 25 percent from the year 2000 to 2020, to about seven and one-half billion people. Most of this increase is projected to be in developing countries located in the tropical zones of the earth. The population of Asia is projected to increase by 800 million, and the population of Africa is projected to double. The International Food Policy Research Institute (IFPRI) has projected that food production will be able to increase such that the world per capita food available will supply about 2,900 kilocalories per person per day in the year 2020, compared to 2,700 kilocalories in 1993. The equitable distribution of food supplies will remain a major problem. The daily food available in sub-Saharan Africa is projected to supply only about 2,300 kilocalories per capita in the year 2020, barely sufficient to support a productive life. IFPRI estimates that one out of every four of the world's children will be malnourished in the year 2020. To achieve the projected increase in food supplies, continued improvements in crop yields will be necessary.

In contrast to the limited food supplies in many developing nations, developed countries are projected to have a food supply that will provide 3,470 kilocalories per capita per day in the year 2020. The U.S. Department of Agriculture indicates that the available food in the United States in 1994 provided 3,800 kilocalories per capita. This food supply provided annually 193 pounds of red meat, poultry, and fish, 585 pounds of dairy products, 194 pounds of cereal products, 151 pounds of fresh, canned, or dried fruits, 208 pounds of fresh, canned, frozen, dried, or fried vegetables and pulses, and 147 pounds of sugar. These figures represent food availability and do not represent actual consumption or account for wastes and losses in marketing and food preparation. Even with the variety of food available, consumers in the United States do not generally meet the dietary guidelines and food guide recommendations. For example, in food consumption surveys, only 38 percent of those surveyed reported consuming the recommended number of servings per day of cereals, 41 percent of the servings of vegetables (heavily weighted toward potatoes and starchy vegetables), and 23 percent of the servings of fruits. The reported diets provided 33 percent of the energy from fats and 11 percent from saturated fats. Food choices by consumers appear to depend on a variety of factors, such as cost, food preferences, convenience of preparation, and cultural norms, in addition to perception as to effects on health.

Food safety. In addition to providing nutrients, food can also potentially be a source of harm to a consumer. Hazards associated with food include microbiological pathogens, naturally occurring toxins, allergens, intentional and unintentional additives, modified food components, agricultural chemicals, environmental contaminants, and animal drug residues. It has been estimated that more than 80 million cases of food-borne illness occur annually in the United States, resulting in more than 9,000 deaths, primarily from microbiological contamination. The transformation of a safe food into a potentially dangerous one can occur anywhere in a food system that consists of producers, shippers, processors, wholesalers, retailers, and consumers.

An effective food safety system requires regulation, surveillance, consumer education, and continued research to detect and prevent food-borne illnesses. The increase in world trade in food also involves international dimensions in food safety issues. Import regulations dealing with food safety may also have the effect of restricting access to markets, and food safety becomes an issue in world trade.

The United States has a complex system of food-safety regulation. The Food and Drug Administration (FDA) is responsible for domestic and imported foods in interstate commerce except for poultry and meat products. The FDA has responsibility for standards for food labeling, inspects food-processing plants, and regulates food animal drugs and feed additives and all food additives. The Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA) inspects meat and poultry products to ensure they are safe and correctly marked, labeled, and packaged. The Environmental Protection Agency (EPA) licenses pesticide products and establishes tolerances for pesticide residues in food products and animal feeds. The Centers for Disease Control and Prevention (CDC) are responsible for surveillance of illnesses associated with food consumption in association with the FDA and the USDA. These agencies also collaborate with state and local public health agencies that are concerned with food safety.

The consumption and preparation of food also has great social and cultural significance, contributing to the daily enjoyment of life. Public health concerns about dietary practices often must compete with these values as an individual makes food choices. This makes the issues associated with food and nutrition more complex than the medical and public health issues discussed here.

(SEE ALSO: Blood Lipids; Energy; Foods and Diets; Nutrition in Health Departments)

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— MALDEN C. NESHEIM

For more information on nutrition, visit Britannica.com.

1. The process of taking in and assimilating nutrients.

2. The study of food in relation to the physiological processes used to acquire sufficient nutrients to maintain good health.

Food is comprised of nutrients that are classified by their role in the body: the energy-yielding macronutrients (carbohydrates, protein, and fat), the essential micronutrients (vitamins, minerals, and water), and numerous other components. Although micronutrients do not supply energy to fuel the body, they are indispensable for the proper functioning of the metabolic and regulatory activities in the body. Other nonessential nutrients, such as flavonoids, phytoestrogens, carotenoids, and probiotics, also may have important health-promoting properties, and investigations are ongoing. The daily intake of a variety of foods provides energy and nutrients that are essential to the health and well-being of an individual. The relationships among food intake, nutrition, and health define the field of nutrition. More fully, nutrition is the study of food, its nutrients and chemical components, and how these constituents act and interact within the body to affect health and disease.

The scope of the field has grown in recent years and the boundaries between the science of nutrition and many other biological sciences have blurred. For example, the science of nutrition includes chemistry to study how food ingredients interact with each other; physiology to investigate how nutrients within food are assimilated into body tissues; engineering to design new fortified foods; anthropology to explore why we chose to eat certain foods in centuries past; and psychology to determine what attitudes and behaviors influence our dietary patterns today. Nutritionists often have either a college or advanced degree in nutrition or a related field, whereas clinical (human) nutrition specialists will have graduate degrees, which may include medicine, and have completed an examination for certification. Registered dietitians are nutrition professionals who are often responsible for applying nutritional science to clinical practice to promote health and treat disease. Dietitians frequently work in hospitals but also may be employed in universities, public health departments, restaurants, the food industry, and exercise facilities. Similarly, given the broad scope of the field, other nutrition professionals include but are not limited to physicians, biochemists, anthropologists, epidemiologists, geneticists, food scientists, and engineers.

For this review, the field of nutrition is divided into three major categories: (1) nutrition in research, (2) nutrition in clinical practice, and (3) nutrition in policy and education. An overview of nutritional research is presented, from how nutrients interact within the body and among themselves (nutritional biochemistry), to the investigation of the relationships between specific foods or food groups and the health status of populations (nutritional epidemiology). Research findings in the field provide the information needed to guide nutrition practice for the care of individuals as well as large groups of people. The development of nutrition policy comes from both research and clinical practice advances. Concise descriptions of each are given and a brief history of the field and projected directions of the future of the field are offered.

Nutrition: a Historical Perspective

Numerous advances in the field of nutrition have occurred within the last century. The major focus of nutrition research and practice shifted from concern over which foods are required to avoid nutritional deficiencies and overt illness, to what foods and supplements may be consumed to promote optimal health. Functional foods are a part of the vocabulary, and energy bars, herbal remedies, and nutritional supplement products are now widely available.

In biblical times certain foods were understood to have special healing properties; however, the concept of nutrients as essential for health is relatively new. Recent discoveries in the field have been dependent on the development of scientific methods to analyze nutrient content and interactions. Therefore, though some vitamins were understood to be essential in the early part of the twentieth century, trace elements such as zinc and selenium were not considered essential for humans until the 1970s.

As the field of nutrition has developed, it has also expanded. In 1950 the history of nutrition science during the two previous centuries was summarized by Dr. Elmer McCollum in just under five hundred pages. It would likely take ten volumes of such texts to encapsulate the nutrition-related findings and proceedings from the latter half of the twentieth century. Accomplishments in the field of nutrition over the last century are highlighted in five major eras: (1) food as energy, (2) micronutrient deficiency diseases, (3) nutrition in public policy, (4) nutrition and chronic disease, and (5) nutrition for optimal health.

Food as energy (1880–1920). By the end of the nineteenth century the major, energy-yielding components of food—protein, fat, and carbohydrate—had been identified, and nutrition research, especially concerning the metabolism of proteins and the energy composition of foods, was flourishing. Much of this work had been conducted in animals; therefore, the human nutrition experiments performed by Dr. W. O. Atwater (1844–1907) and colleagues were particularly novel. From their studies, the energy yield of carbohydrate, protein, and fat was derived (4, 4, and 9 kcal per gram, respectively), values that are still used today. Dr. Atwater also developed the first human calorimeter in the United States to measure energy expenditure. However, it was a pair of medical doctors, James Harris and Francis Gano Benedict, who perfected this methodology to establish standards for the energy needs of healthy individuals. Energy expenditure was measured in approximately 250 healthy men and women at the Carnegie Institute Laboratory in Washington, D.C., and equations were derived from the data. The Harris-Benedict energy expenditure prediction equations for men and women, published in 1919, remain some of the most useful tools in clinical nutrition assessment today.

Micronutrient deficiency diseases (1920–1940). The period between 1920 and 1940 brought about a paradigm shift in the understanding of the etiology of some common diseases. Until this time it was thought that all disease resulted from poor sanitation and hygiene; therefore, bacteria, mold, and toxins were identified as the likely cause of disease. As Alfred Harper has suggested, "the concept that a disease might be caused by a deficit of a substance that was nutritionally essential was beyond the grasp even of most nineteenth-century physicians and scientists" (p. 217). In order to combat disease as well as increase shelf life, food was sterilized, milled, and polished to reduce the danger of ingesting bacteria, mold, and toxins. Despite these efforts, pellagra, beriberi, and infantile scurvy actually increased in prevalence. In a number of studies conducted by Dr. Joseph Goldberger from 1914 to the 1920s, where the diets of individuals suffering from pellagra were compared to those of healthy individuals, foods that decreased the presence of diarrhea and dementia in pellagrous individuals were identified. From his work it was later determined that pellagra was due to a diet poor in the vitamin niacin and not infection. At approximately the same time, Dr. Christiaan Eijkman (1858–1930) won a Nobel Prize in medicine (1929) for the discovery of the "antineuritic" vitamin thought to be responsible for curing beriberi. Through his experiments, in which chickens were fed human hospital diets, combined with studies of beriberi in prisoners who survived on polished rice, he hypothesized that the hull of the rice grain contained an antidote to the neurological disorder. Although not completely correct, his observations led to the discovery of the essential vitamin thiamin.

As Kenneth J. Carpenter summarized, "new technologies of food processing that have obvious advantages may also have a downside" (p. 227). While technology decreased infectious disease and increased the shelf life of food products, it inadvertently led to nutritional deficiencies. The heat-sterilization of cow's milk, which destroyed vitamin C, was related to the outbreak of infantile scurvy in well-to-do families. The practices of polishing rice and degerming corn to increase grain stability also led to increased prevalence of beriberi (thiamin deficiency) and pellagra (niacin deficiency), respectively.

Nutrition in public policy (1920–1964). One of the most fruitful periods in the history of public health nutrition followed on the coattails of World War I. It became possible to manufacture the micronutrients that had been identified by chemists as essential for health cheaply and efficiently. In 1922 the first of a series of public health efforts at eradicating nutrient deficiency in the United States was initiated by the voluntary addition of iodine to salt (see Table 1). The fortification of other foods was used to address rampant public health problems such as rickets (vitamin D), beriberi (thiamin), pellagra (niacin), and dental caries (fluoride). Since the initiation of fortification policies in the United States, clinically evident nutritional deficiencies have been virtually eliminated.

The first attempt at defining nutritional requirements was directed toward the prevention of nutrient deficiencies in military personnel during World War II. In the early 1940s the Food and Nutrition Board of the National Academy of Sciences reviewed the scientific evidence and developed the Recommended Dietary Allowances for energy, protein, and eight essential vitamins and minerals. The first national food supplementation program was initiated in 1946 (National School Lunch Act) to improve the dietary intake of children from economically disadvantaged families. Other national food assistance programs were added over the next fifty years.

Nutrition and chronic disease (1960–1990). The last forty years of the twentieth century saw continued discovery in the field of nutritional biochemistry and a new research emphasis on the role of nutrition in the cause of and treatment for chronic disease. Disease patterns shifted from infectious and nutrient deficiency diseases to increasing rates of cardiovascular disease, diabetes, cancer, and osteoporosis. Nutrient deficiencies, when present, were often secondary to restrictive dietary habits, economic deprivation, or the presence of another disease that altered nutrient metabolism. The more pressing problem now was the change in the American lifestyle and a dietary shift from too little to too much. Modern household technologies increased productivity in housework but decreased physical activity, and the home-cooked family meal became a thing of the past. Varied diets consisting of whole grains, fruits, and vegetables gave way to convenience foods resulting in a much higher consumption of fat and sugar. Results from the Framingham Heart Study were perhaps the first glimpse into the relationship between fat intake and cardiovascular disease and the realization that each type of fat plays a specific role in health and disease. During this era, links among fat intake, serum cholesterol, and cardiovascular disease were studied thoroughly, and the reasons for the increasing prevalence of obesity in the United States were explored. In 1985 Michael Brown and Joseph Goldstein were awarded the Nobel Prize in medicine for their work on the regulation of cholesterol metabolism and its influence on arteriosclerosis.

The essentiality of macrominerals (e.g., calcium, phosphorus, sodium) was understood in the 1850s. However, it was not until technological advances triggered an explosion of new research that trace and ultra-trace elements were identified as essential for humans. Working together, nutritionists, biochemists, biologists, immunologists, geneticists, and epidemiologists uncovered the mysteries behind minerals such as zinc, selenium, copper, molybdenum, and chromium. Scientists first recognized human zinc deficiency in the mid-1960s. Severely growth-retarded, young Middle Eastern men were anemic, extremely lethargic, and hypogonadal. Their diet consisted mainly of wheat bread with little animal protein. When their diets were supplemented with zinc, their lethargy, growth, and genital development improved.

Table 1

Nutrition for optimal health (1990–present). In the understanding of nutrition, the American public experienced yet another paradigm shift in the 1990s. They wondered if all nutrients that provided a health benefit needed to fit the traditional definition of "essential nutrient." As a result of this question, herbal and botanical extracts, phytochemicals, and other alternative nutritional therapies to promote optimum health were explored. In 1999 the U.S. market for functional foods alone was estimated to be $6 billion (Hasler, p. 504) and it continues to grow by approximately 12 percent each year. The explosion of this market is likely due to the increase in social acceptance, changes in regulations, the booming economy of the 1990s, and the targeting of products to particular populations. The scientific validation of some therapies also is of increasing interest.

Pharmacological uses (larger amounts than required to prevent deficiencies) of essential nutrients are being explored. Although much of the current interest in megavitamin supplementation began in the 1990s, the work of Dr. Linus Pauling in the 1970s initiated the movement. Pauling was the only individual to be awarded two unshared Nobel prizes for his work in chemistry (1954) and peace (1962). In the field of nutrition, however, he is noted most for his unproven theories regarding the potential protective role of vitamin C on the common cold, cancer, and heart disease. Pauling himself reportedly took up to six hundred times the recommended daily amount of vitamin C. Given that many individuals also practice a "more must be better" approach, the national recommendations for nutrient intake now include guidelines for safe upper limits for individual nutrient intakes.

Nutrition in Research

Experimental nutrition research is one aspect of the science of nutrition. Nutrition research is conducted to answer questions raised both in clinical practice and policy. Research in nutrition can focus on individual cells, whole animals or humans, or entire populations, and often overlaps with research in genetics, biochemistry, molecular biology, toxicology, immunology, physiology, and pharmacology.

Nutritional biochemistry. Nutritional biochemistry is the backbone to the understanding of the structure and function of nutrients within food and the body. Nutrients serve as cofactors for enzymes, components of hormones, and participants in oxidation/reduction reactions through metabolic processes. Though required in small amounts, nutrients are essential for body growth, sexual development and reproduction, psychological well-being, energy level, and the normal functioning of most organ systems in the body. Nutritional biochemists study the functional roles of vitamins and minerals in the body, metabolic blocks that occur from deficiencies, the effects of hormones on nutrient metabolism, and interactions among nutrients within the body. In the 1990s a whole new area of research emerged that focuses on relationships between nutrition and genetics. An example of this type of study includes the identification of a genetic defect in folate metabolism (C677T), which increases a woman's risk of delivering a baby with a neural tube defect.

Food science. Food science is the study of the composition of food materials and the reaction of food to processing, cooking, packaging, and storage. Food science integrates knowledge of the chemical composition of food materials; their physical, biological, and biochemical behavior; the interaction of food components with each other and their environment; pharmacology and toxicology of food materials, additives, and contaminants; and the effects of manufacturing operations, processes, and storage conditions.

The potential beneficial role of functional foods in the American diet has gained attention and recent food science research focuses on the development of such foods. Functional foods are generally defined as those that provide health benefits beyond basic nutrition, and include fortified, enriched, or enhanced foods, and whole foods, which have high levels of protective nutrient components. Examples of these foods include orange juice with added calcium or echinacea, or snack foods with antioxidants, fruit-flavored candy with vitamin C, various soy products, and margarine with added plant sterols. Factors that drive the market for such foods include a growing general public interest in nutrition and its impact on health, an aging population that is more concerned with health, research findings receiving media attention, and an increasingly unregulated consumer food market.

Human nutrition. Human nutrition, or clinical nutrition, research is that which focuses on the study of nutrients within the living human body. Although biochemical studies are extremely informative, until the nutrient is added to or depleted from the diet, the effects on individuals can only be hypothesized. Human nutrition research includes the study of individual nutrient requirements (e.g., nutrient intake assessment, energy expenditure assessment, nutrient turnover balance studies, and nutrient bioavailability), the effects of nutrients on body growth (e.g., body composition techniques, anthropometry, pubertal assessment), and the dietary, physiological, or disease factors that influence nutrient requirements. In the 1990s one important human nutrition study found that increasing folic acid intake in young women reduces the incidence of neural tube defects (spina bifida) in their babies.

Nutritional epidemiology. Nutritional epidemiology is the science of systematically studying the relationships between food choices and health status. Epidemiological studies are particularly valuable in understanding complex relationships between food intake (dietary exposure) and determinants of diseases with multiple etiologies and long latent periods. Examples of such studies include the relationships between low folic acid intake and increased incidence of spina bifida, and elevated saturated fat intake and elevated risk of arteriosclerosis. There are, however, limitations to these studies in that they describe relationships rather than prove cause and effect. Frequently, clinical trials and intervention studies are used as follow-up studies to evaluate more fully the questions raised by epidemiological evidence.

Nutrition in Clinical Practice

Scientific evidence continues to mount regarding the key roles that nutrients and their metabolism play in the prevention of the most common chronic diseases. Half of the leading causes of death in the United States (heart disease, cancer, stroke, and diabetes) are associated strongly with unhealthy eating habits. Clinical nutrition is the practice of applying research evidence to aid in the care of individuals with or at risk for diet-related diseases. These principles are used to develop individualized nutrition care plans. Generally, diseases may affect nutritional status by (a) decreasing the intake of nutrients, (b) altering the metabolism of nutrients (or unusual losses), or (c) altering energy expenditure. Alternatively, as mentioned briefly above, poor nutritional status can lead to disease. For example, zinc deficiency can decrease the function of the immune system that in turn leads to increased risk for diarrhea and infectious diseases.

Assessment of nutritional status is essential for identifying undernourished and overnourished states (obesity is now a major health problem) and estimating the optimum intake to promote normal growth and well-being. Nutritional assessment has several components, including the evaluation of dietary intake, growth status, body composition, energy expenditure, and biochemical measures of nutritional status in the context of a medical history, diagnoses, and current therapy. These data are used to develop individualized nutritional care plans, which may include recommendations for total energy intake, adjustments in the diet to increase or decrease the consumption of certain foods, and possibly the inclusion of nutrient supplements. For patients who cannot be fed orally, more technology-based nutritional support is used to maintain or improve nutrient intakes and nutritional status. This involves either feeding the patient through a tube directly into the stomach or intestine (enteral) or through an intravenous line directly into the bloodstream (parenteral). Because malnutrition will add to complications of illness and prolong the illnesses and hospitalization, appropriate assessment of the patient is extremely important. In the complex and rapidly changing context of critical illness, individualized nutrition assessments are crucial and require the sequential monitoring of all patients to maintain appropriate nutritional care plans.

It is unlikely that individuals who have not been seriously ill have had the opportunity to seek the counsel of a trained nutritional professional for developing an individualized diet plan. The average American displays a keen interest in how nutrition affects his or her health, and is disappointed with the information physicians are able to provide because traditional medical training has limited nutrition content. Therefore, greater numbers of individuals are seeking nutrition information for themselves, and using the information to self-diagnose and self-prescribe. The advances in communications technology, particularly the explosion of information on the World Wide Web, allow the ready accessibility of sound nutritional advice, and substantial amounts of quackery. Without training and a significant amount of time dedicated to the task, it is difficult to decipher truth from fraud. Future directions in nutritional education likely will include tools to aid Americans in deciphering information, particularly from the Internet, in order to make educated choices to optimize their diets and live healthier lives (see Table 2).

Nutrition in Public Policy: Monitoring and Education

Nutrition in public health or nutrition policy generally is regarded as the combined efforts taken toward improving nutrition and health status of populations. With increasing emphasis on health promotion and disease prevention, there is a proliferation of nutrition-related disease prevention, screening, and education programs targeted at increasing fiber, fruit, and vegetable intake, and reducing saturated fat intake. Additionally, a number of food assistance programs and mandated food fortification programs have been instituted, all promoting a healthy diet and lifestyle.

Table 2

Nutrition research, public policy programs, and nutrition surveillance systems work synergistically like spokes on a wheel. Evidence obtained from scientific research is used to set nutritional recommendations such as the Dietary Reference Intakes and the Dietary Guidelines for Americans. These standards are used to judge the adequacy of the American diet, provide the basis for nutrition labeling of foods, formulate special diets, and guide the development of food fortification and nutrition policy developed to assist those who are at nutritional risk. Specific food assistance programs (such as, food stamps, Special Supplementary Nutrition Program for Women, Infants, and Children) are targeted at specific economically disadvantaged and nutritionally at-risk populations. Fortification programs generally are less specific, but some target at-risk populations through specific foods, for example, vitamin D–fortified milk to prevent rickets in young children. Finally, the wheel is completed by nutrition monitoring programs that are used to evaluate the effectiveness of instituted policies. The National Health and Nutrition Examination Survey (NHANES) and the Continuing Survey of Food Intake of Individuals (CSFII) are ongoing monitoring tools used to assess the population's nutrient intakes, nutrition and health status, and knowledge and attitudes about health.

Perhaps most important, public health nutrition includes the dissemination of scientific findings, the explanation of dietary recommendations, and outreach of federal assistance programs. The responsibility of communicating experimental findings in an understandable form falls on nutrition scientists, journalists, educators, and the public. The scientists are responsible for interpreting the research findings into a form that is understandable to the general public. Journalists are responsible for communicating the scientific message in an objective way, and the public is responsible for pursuing an accurate understanding of the issues. Various government agencies have the responsibility to organize and administrate the myriad of nutritional policies and programs, and to communicate information regarding these programs to the public.

The Future of Nutrition and Food Science

In the twentieth century nutrition research, practice, and public policy shifted from a focus on the quantitative aspects—to ensure food security and eradicate nutritional deficiencies—to a greater attention on the qualitative aspects—to achieve optimal, balanced, dietary intakes. In the twenty-first century nutrition research, practice, and policy will likely explore the following areas:
relationships between human genetics and nutrition, the role of genetically modified foods in human health,
the relationship of nonfood substances in the promotion of health and the bioengineering of functional foods,
the promotion of economic growth and food security in developing nations to prevent or delay the undesirable health effects of malnutrition, and
the prevention and treatment of the obesity epidemic in children and adults.

Relationships between food intake and human health will continue to be of great public interest, and nutrition and food scientists will face new challenges in a fasterchanging environment.

PROFESSIONAL NUTRITION CREDENTIALS IN THE UNITED STATES class='shw'>Definition of Terms

Table 3

Nutrition: the study of foods, their nutrients, and other chemical components; their actions and interactions in the body; and their influence on health and disease.

Nutritional Science: the body of scientific knowledge that relates to the processes involved in nutrition.

Health: a state of optimal well-being—physical, mental, and social; relative freedom from disease.

Functional Foods: foods that provide a health benefit beyond basic nutrition.

Essential Nutrient: a substance that must be obtained from the diet because the body either cannot make it or cannot make adequate amounts.

Enteral Nutrition: nutrient solutions delivered into the gastrointestinal tract (e.g., stomach, small intestine) through a tube inserted through the nose or directly into the stomach.

Parenteral Nutrition: nutrient solutions delivered directly into the bloodstream through an intravenous catheter.

Bibliography

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American Dietetic Association. Nutrition and You: Trends 2000. Chicago, Ill.: American Dietetic Association, 2000.

Carpenter, Kenneth J. "Vitamin Deficiencies in North America in the 20th Century." Nutrition Today 34 (1999): 223–228.

Committee on Diet and Health, Food and Nutrition Board, National Research Council. Diet and Health: Implications for Reducing Chronic Disease Risk. Washington, D.C.: National Academy Press, 1989.

Dupont, Jacqueline. "The Third Century of Nutrition Research Policy—Shared Responsibility." Nutrition Today 34 (1999): 234–241.

Food and Nutrition Board. Recommended Dietary Allowances. National Research Council Reprint and Circular Series No. 115. Washington, D.C.: National Research Council, 1943.

Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes. Washington, D.C.: National Academy Press, 1997. Studies on calcium, phosphorus, magnesium, vitamin D, and fluoride.

Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes. Washington, D.C.: National Academy Press, 1988. Studies on thiamin, riboflavin, niacin, vitamin B ₆, folate, vitamin B ₁₂, pantothenic acid, biotin, and choline. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes. Washington, D.C.: National Academy Press, 2001. Studies on vitamins A and K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdemum, nickel, silicon, vanadium, and zinc.

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—Ellen B. Fung; Virginia A. Stallings

1. the sum of the processes involved in taking in nutriments and assimilating and utilizing them.
2. nutriment.
It includes all the processes by which the body uses food for energy, maintenance and growth. See also malnutrition, inanition, starvation, thirst, nutritional.

• critical care n. — provision of nutritional support for patients in critical care units; usually requires modification of normal nutritional requirements to meet the demands of stress, injury and disease, and to support recovery from these states.
• enteral n. — see enteral feeding.
• intravenous n. — see parenteral nutrition (below).
• N. Labeling and Education Act of 1990 — an amendment to the (US) Federal Food, Drug, and Cosmetic Act which defines how foods, claimed to affect disease, are not regulated as drugs.
• parenteral n. — a technique for meeting a patient's nutritional needs by means of intravenous feeding; sometimes called hyperalimentation, even though it does not provide excessive amounts of nutrients. Nutrition by intravenous feeding may be total parenteral nutrition (TPN) or supplemental. TPN provides all of the carbohydrates, proteins, fats, water, electrolytes, vitamins and minerals needed for the building of tissue, expenditure of energy, and other physiological activities.
• total parenteral n. — called also TPN; see parenteral nutrition (above).

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The "Nutrition Facts" table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts.

Nutrition (also called nourishment or aliment) is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life. Many common health problems can be prevented or alleviated with a healthy diet.

The diet of an organism refers to what it eats. Dietitians are health professionals who specialize in human nutrition, meal planning, economics, preparation, and so on. They are trained to provide safe, evidence-based dietary advice and management to individuals (in health and disease), as well as to institutions.

Poor diet can have an injurious impact on health, causing deficiency diseases such as scurvy, beriberi, and kwashiorkor; health-threatening conditions like obesity and metabolic syndrome, and such common chronic systemic diseases as cardiovascular disease, diabetes, and osteoporosis.

Contents 1 Overview 2 Nutrients 2.1 Carbohydrates 2.2 Fat 2.2.1 Essential fatty acids 2.3 Fiber 2.4 Protein 2.5 Minerals 2.5.1 Macrominerals 2.5.2 Trace minerals 2.6 Vitamins 2.7 Water 2.8 Other nutrients 2.8.1 Antioxidants 2.8.2 Phytochemicals 2.9 Intestinal bacterial flora 3 Advice and guidance 3.1 Governmental policies 3.2 Teaching 4 Healthy diets 4.1 Whole plant food diet 4.2 The French "paradox" 5 Sports nutrition 5.1 Protein 5.2 Water and salts 5.3 Carbohydrates 6 Malnutrition 6.1 Illnesses caused by improper nutrient consumption 6.2 Mental agility 6.3 Mental disorders 6.4 Cancer 6.5 Metabolic syndrome 6.6 Hyponatremia 7 Processed foods 8 History 8.1 From antiquity to 1900 8.2 From 1900 to the present 9 See also 10 Further reading 11 References 12 External links 12.1 Databases and search engines

Overview

Nutritional science investigates the metabolic and physiological responses of the body to diet. With advances in the fields of molecular biology, biochemistry, and genetics, the study of nutrition is increasingly concerned with metabolism and metabolic pathways: the sequences of biochemical steps through which substances in living things change from one form to another.

The human body contains chemical compounds, such as water, carbohydrates (sugar, starch, and fiber), amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA and RNA). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, calcium, iron, zinc, magnesium, manganese, and so on. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones, vitamins, phospholipids, hydroxyapatite), both in the human body and in the plant and animal organisms that humans eat.

The human body consists of elements and compounds ingested, digested, absorbed, and circulated through the bloodstream to feed the cells of the body. Except in the unborn fetus, the digestive system is the first system involved. In a typical adult, about seven liters of digestive juices enter the lumen of the digestive tract.^{[citation needed][clarification needed]} These break chemical bonds in ingested molecules, and modulate their conformations and energy states. Though some molecules are absorbed into the bloodstream unchanged, digestive processes release them from the matrix of foods. Unabsorbed matter, along with some waste products of metabolism, is eliminated from the body in the feces.

Studies of nutritional status must take into account the state of the body before and after experiments, as well as the chemical composition of the whole diet and of all material excreted and eliminated from the body (in urine and feces). Comparing the food to the waste can help determine the specific compounds and elements absorbed and metabolized in the body. The effects of nutrients may only be discernible over an extended period, during which all food and waste must be analyzed. The number of variables involved in such experiments is high, making nutritional studies time-consuming and expensive, which explains why the science of human nutrition is still slowly evolving.

In general, eating a wide variety of fresh, whole (unprocessed), foods has proven favorable compared to monotonous diets based on processed foods.^{[citation needed]} In particular, the consumption of whole-plant foods slows digestion and allows better absorption, and a more favorable balance of essential nutrients per Calorie, resulting in better management of cell growth, maintenance, and mitosis (cell division), as well as better regulation of appetite and blood sugar. Regularly scheduled meals (every few hours) have also proven more wholesome than infrequent or haphazard ones.^{[citation needed]}

Nutrients

Main article: Nutrient

There are seven major classes of nutrients: carbohydrates, fats, fiber, minerals, protein, vitamins, and water.

These nutrient classes can be categorized as either macronutrients (needed in relatively large amounts) or micronutrients (needed in smaller quantities). The macronutrients are carbohydrates, fats, fiber, proteins, and water. The micronutrients are minerals and vitamins.

The macronutrients (excluding fiber and water) provide energy, which is measured in Joules or kilocalories (often called "Calories" and written with a capital C to distinguish them from gram calories). Carbohydrates and proteins provide 17 kJ (4 kcal) of energy per gram, while fats provide 37 kJ (9 kcal) per gram.^[1] Vitamins, minerals, fiber, and water do not provide energy, but are necessary for other reasons.

Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch). Fats are triglycerides, made of various fatty acid monomers bound to glycerol. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to the elements of carbohydrates and fats. The nitrogen-containing monomers of protein are amino acids, and they include some essential amino acids. They fulfill many roles other than energy metabolism; and when they are used as fuel, getting rid of the nitrogen places a burden on the kidneys.

Other micronutrients include antioxidants and phytochemicals.

Most foods contain a mix of some or all of the nutrient classes. Some nutrients are required regularly, while others are needed only occasionally. Poor health can be caused by an imbalance of nutrients, whether an excess or a deficiency.

Carbohydrates

Main article: Carbohydrate

A pack of toasted bread is a cheap, high calorie nutrient (usually unbalanced, i.e., deficient in essential minerals and vitamins, because of removal of grain bran) food source with a long shelf-life.

Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides by the number of monomer (sugar) units they contain. They constitute a large proportion of foods such as rice, noodles, bread, and other grain-based products. Monosaccharides contain one sugar unit, disaccharides two, and polysaccharides three or more. Polysaccharides are often referred to as complex carbohydrates because they are long chains of sugar units, whereas monosaccharides and disaccharides are simpler. The difference is important: complex carbohydrates take longer to digest and absorb since their sugar units are processed one-by-one off the ends of the chains. The spike in blood-sugar levels after ingestion of simple sugars is thought to be involved in causing heart and vascular disease. Simple sugars form a greater part of modern diets, leading to more cardiovascular disease in populations. Simple carbohydrates are absorbed quickly, and therefore raise blood-sugar levels more rapidly.

Fat

Main article: Fat

A molecule of fat consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone). Fats may be classified as saturated or unsaturated. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded, so their molecules have relatively few hydrogen atoms. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Trans fats are a type of unsaturated fat with trans-isomer fatty acid, typically created in an industrial process called (partial) hydrogenation.

Many studies have shown that unsaturated fats, particularly monounsaturated fats, are best in the human diet. Saturated fats, typically from animal sources, are next, while trans fats are to be avoided. Saturated and trans fats are typically solid at room temperature (such as butter or lard), while unsaturated fats are typically liquids (such as olive oil or flaxseed oil). Trans fats are very rare in nature, but have properties useful in the food processing industry.^{[citation needed]}

Essential fatty acids

Main article: Essential fatty acids

Most fatty acids are non-essential, meaning the body can produce them as needed. However, in humans at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—is important for health. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. They are hormones, in some respects. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (LNA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g. weakly inflammatory PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as a building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 linoleic acid (LA) in the human body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins: one reason a balance between omega-3 and omega-6 is important for cardiovascular health. In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids.

The conversion rate of omega-6 DGLA to AA largely determines the production of the prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE2 (made from AA) toward anti-inflammatory PGE1 (made from DGLA). Moreover, the conversion (desaturation) of DGLA to AA is controlled by the enzyme delta-5-desaturase, which in turn is controlled by hormones such as insulin (up-regulation) and glucagon (down-regulation). The amount and type of carbohydrates consumed, along with some types of amino acid, can influence processes involving insulin, glucagon, and other hormones; therefore the ratio of omega-3 versus omega-6 has wide effects on general health, and specific effects on immune function and inflammation, and mitosis (i.e. cell division).

Good sources of essential fatty acids include most vegetables, nuts, seeds, and marine oils,^[2] Some of the best sources are fish, flax seed oils, soy beans, pumpkin seeds, sunflower seeds, and walnuts.

Fiber

Main article: Dietary fiber

Fiber is a carbohydrate (or a polysaccharide) that is incompletely absorbed in humans and in some other animals. Like all carbohydrates, when it is metabolized it can produce four Calories (kilocalories) of energy per gram. But in most circumstances it accounts for less than that because of its limited absorption. Dietary fiber consists mainly of cellulose, a large carbohydrate polymer that is indigestible because humans do not have the required enzymes. There are two subcategories: soluble and insoluble fiber. Whole grains, fruits (especially plums, prunes, and figs), and vegetables are rich in dietary fiber. Fiber is important to digestive health and is thought to reduce the risk of colon cancer.^{[citation needed]} It can help in alleviating both constipation and diarrhea. Fiber provides bulk to the intestinal contents, and insoluble fiber stimulates peristalsis: the rhythmic muscular contractions passing along the digestive tract. Some soluble fibers produce a solution of high viscosity: a gel, which slows the movement of food through the intestines. Fiber, especially from whole grains, may help lessen insulin spikes and reduce the risk of diabetes [type 2].

Protein

Most meats such as chicken contain all the essential amino acids needed for humans

Main article: Protein in nutrition

Proteins are the basis of many animal body structures (e.g. muscles, skin, and hair). Each molecule is composed of amino acids which are characterized by inclusion of nitrogen and sometimes sulphur. The body requires amino acids to produce new proteins (protein retention) and to replace damaged proteins (maintenance). Excess amino acids are discarded, typically in the urine. For all animals, some amino acids are essential (an animal cannot produce them internally) and some are non-essential (the animal can produce them from other nitrogen-containing compounds). About twenty amino acids are found in the human body, and about ten of these are essential, and therefore must be included in the diet. A diet that contains adequate amounts of amino acids (especially those that are essential) is particularly important when there is greater need: in early development and maturation, pregnancy, lactation, or injury. A complete protein source contains all the essential amino acids; an incomplete protein source lacks one or more of the essential amino acids. It is possible to combine two incomplete protein sources (e.g. rice and beans) to make a complete protein source. Sources of dietary protein include meats, tofu and other soy-products, eggs, grains, legumes, and dairy products such as milk and cheese. A few amino acids from protein can be converted into glucose and used for fuel through a process called gluconeogenesis. The amino acids remaining after such conversion are discarded.

Minerals

Main article: Dietary mineral

Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen that are present in common organic molecules. The term "mineral" is archaic, since the intent is to describe simply the less common elements in the diet: heavier than the four just mentioned; including several metals; and often occurring as ions in the body. Some dietitians recommend that these be supplied from foods in which they occur naturally, or at least as complex compounds, or sometimes even from natural inorganic sources (such as calcium carbonate from ground oyster shells). On the other hand, minerals are often artificially added to the diet as supplements, the most famous being iodine in iodized salt.

Macrominerals

Many elements are essential in quantity; also called "bulk minerals". Some are structural, but many play a role as electrolytes.^[3] Elements with recommended dietary allowance (RDA) greater than 200 mg/day are the following, in alphabetical order (with informal or folk-medicine perspectives in parentheses):

• Calcium, a common electrolyte, but also structural (for muscle and digestive system health, builds bone, neutralizes acidity, clears toxins, helps blood stream)
• Chlorine as chloride ions; very common electrolyte; see sodium, below
• Magnesium, required for processing ATP and related reactions (builds bone, causes strong peristalsis, increases flexibility, increases alkalinity)
• Phosphorus, required component of bones; essential for energy processing^[4]
• Potassium, a very common electrolyte (heart and nerve health)
• Sodium, a very common electrolyte; not generally found in dietary supplements, despite being needed in large quantities, because the ion is very common in food: typically as sodium chloride, or common salt
• Sulfur for three essential amino acids and therefore many proteins (skin, hair, nails, liver, and pancreas)

Trace minerals

Many elements are required in trace amounts, usually because they play a catalytic role in enzymes.^[5] Some trace mineral elements (RDA < 200 mg/day) are, in alphabetical order:

• Cobalt required for biosynthesis of vitamin B12 family of coenzymes
• Copper required component of many redox enzymes, including cytochrome c oxidase
• Chromium required for sugar metabolism
• Iodine required for the biosynthesis of thyroxin; needed in larger quantities than others in this list, and sometimes classified with the macrominerals
• Iron required for many enzymes, and for hemoglobin and some other proteins
• Manganese (processing of oxygen)
• Molybdenum required for xanthine oxidase and related oxidases
• Nickel present in urease
• Selenium required for peroxidase (antioxidant proteins)
• Vanadium (Speculative: there is no established RDA for vanadium. No specific biochemical function has been identified for it in humans, although vanadium is found in lower organisms.)
• Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase

Vitamins

Main article: Vitamin

As with the minerals discussed above, twelve vitamins are recognized as essential nutrients, necessary in the diet for good health. (Vitamin D is the exception: it can alternatively be synthesized in the skin, in the presence of UVB radiation.) Certain vitamin-like compounds that are recommended in the diet, such as carnitine, are indispensable for survival and health; but these are not strictly "essential" because the human body has some capacity to produce them from other compounds. Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which may have desirable properties including antioxidant activity (see below). Other essential nutrients not classed as vitamins include essential amino acids (see above), choline, essential fatty acids (see above), and the minerals discussed in the preceding section.

Vitamin deficiencies may result in disease conditions: goitre, scurvy, osteoporosis, impaired immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health (including eating disorders), among many others.^[6] Excess of some vitamins is also dangerous to health (notably vitamin A); and deficiency or excess of minerals can also have serious health consequences.

Water

Main article: Drinking water

A manual water pump in China

About 70% of the non-fat mass of the human body is made of water.^{[citation needed]} To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors.^{[citation needed]} With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

It is not clear how much water intake is needed by healthy people, although some experts assert that 8–10 glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration.^[7] The notion that a person should consume eight glasses of water per day cannot be traced back to a scientific source.^[8] The effect of water intake on weight loss and on constipation is also still unclear.^[9] Original recommendation for water intake in 1945 by the Food and Nutrition Board of the National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."^[10] The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men.^[11] Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicine—who recommend that, on average, women consume 2.2 litres and men 3.0 litres—this is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing.^[12]

For those who have healthy kidneys, it is rather difficult to drink too much water,^{[citation needed]} but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which can be fatal. In particular large amounts of de-ionized water are dangerous.

Normally, about 20 percent of water intake comes in food, while the rest comes from drinking water and assorted beverages (caffeinated included). Water is excreted from the body in multiple forms; including urine and feces, sweating, and by water vapor in the exhaled breath.

Other nutrients

Other micronutrients include antioxidants and phytochemicals. These substances are generally more recent discoveries which: have not yet been recognized as vitamins; are still under investigation; or contribute to health but are not necessary for life. Phytochemicals may act as antioxidants, but not all phytochemicals are antioxidants.

Antioxidants

Main article: Antioxidant

Antioxidants are a recent discovery. As cellular metabolism/energy production requires oxygen, potentially damaging (e.g. mutation causing) compounds known as free radicals can form. Most of these are oxidizers (i.e. acceptors of electrons) and some react very strongly. For normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds. Some are produced by the human body with adequate precursors (glutathione, Vitamin C) and those that the body cannot produce may only be obtained through the diet through direct sources (Vitamin C in humans, Vitamin A, Vitamin K) or produced by the body from other compounds (Beta-carotene converted to Vitamin A by the body, Vitamin D synthesized from cholesterol by sunlight). Phytochemicals (Section Below) and their subgroup polyphenols are the majority of antioxidants; about 4,000 are known. Different antioxidants are now known to function in a cooperative network, e.g. vitamin C can reactivate free radical-containing glutathione or vitamin E by accepting the free radical itself, and so on. Some antioxidants are more effective than others at neutralizing different free radicals. Some cannot neutralize certain free radicals. Some cannot be present in certain areas of free radical development (Vitamin A is fat-soluble and protects fat areas, Vitamin C is water soluble and protects those areas). When interacting with a free radical, some antioxidants produce a different free radical compound that is less dangerous or more dangerous than the previous compound. Having a variety of antioxidants allows any byproducts to be safely dealt with by more efficient antioxidants in neutralizing a free radical's butterfly effect.

Phytochemicals

Blackberries are a source of polyphenol antioxidants

Main article: Phytochemical

A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals. These nutrients are typically found in edible plants, especially colorful fruits and vegetables, but also other organisms including seafood, algae, and fungi. The effects of phytochemicals increasingly survive rigorous testing by prominent health organizations. One of the principal classes of phytochemicals are polyphenol antioxidants, chemicals which are known to provide certain health benefits to the cardiovascular system and immune system. These chemicals are known to down-regulate the formation of reactive oxygen species, key chemicals in cardiovascular disease.

Perhaps the most rigorously tested phytochemical is zeaxanthin, a yellow-pigmented carotenoid present in many yellow and orange fruits and vegetables. Repeated studies have shown a strong correlation between ingestion of zeaxanthin and the prevention and treatment of age-related macular degeneration (AMD).^[13] Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts.^[14] A second carotenoid, lutein, has also been shown to lower the risk of contracting AMD. Both compounds have been observed to collect in the retina when ingested orally, and they serve to protect the rods and cones against the destructive effects of light.

Another carotenoid, beta-cryptoxanthin, appears to protect against chronic joint inflammatory diseases, such as arthritis. While the association between serum blood levels of beta-cryptoxanthin and substantially decreased joint disease has been established, neither a convincing mechanism for such protection nor a cause-and-effect have been rigorously studied.^[15] Similarly, a red phytochemical, lycopene, has substantial credible evidence of negative association with development of prostate cancer.

The correlations between the ingestion of some phytochemicals and the prevention of disease are, in some cases, enormous in magnitude.

Even when the evidence is obtained, translating it to practical dietary advice can be difficult and counter-intuitive. Lutein, for example, occurs in many yellow and orange fruits and vegetables and protects the eyes against various diseases. However, it does not protect the eye nearly as well as zeaxanthin, and the presence of lutein in the retina will prevent zeaxanthin uptake. Additionally, evidence has shown that the lutein present in egg yolk is more readily absorbed than the lutein from vegetable sources, possibly because of fat solubility.^[16] At the most basic level, the question "should you eat eggs?" is complex to the point of dismay, including misperceptions about the health effects of cholesterol in egg yolk, and its saturated fat content.

As another example, lycopene is prevalent in tomatoes (and actually is the chemical that gives tomatoes their red color). It is more highly concentrated, however, in processed tomato products such as commercial pasta sauce, or tomato soup, than in fresh "healthy" tomatoes. Yet, such sauces tend to have high amounts of salt, sugar, other substances a person may wish or even need to avoid.

The following table presents phytochemical groups and common sources, arranged by family:

Family	Sources	Possible Benefits
flavonoids	berries, herbs, vegetables, wine, grapes, tea	general antioxidant, oxidation of LDLs, prevention of arteriosclerosis and heart disease
isoflavones (phytoestrogens)	soy, red clover, kudzu root	general antioxidant, prevention of arteriosclerosis and heart disease, easing symptoms of menopause, cancer prevention[17]
isothiocyanates	cruciferous vegetables	cancer prevention
monoterpenes	citrus peels, essential oils, herbs, spices, green plants, atmosphere[18]	cancer prevention, treating gallstones
organosulfur compounds	chives, garlic, onions	cancer prevention, lowered LDLs, assistance to the immune system
saponins	beans, cereals, herbs	Hypercholesterolemia, Hyperglycemia, Antioxidant, cancer prevention, Anti-inflammatory
capsaicinoids	all capiscum (chile) peppers	topical pain relief, cancer prevention, cancer cell apoptosis

Intestinal bacterial flora

Main article: Gut flora

It is now also known that animal intestines contain a large population of gut flora. In humans, these include species such as Bacteroides, L. acidophilus and E. coli, among many others. They are essential to digestion, and are also affected by the food we eat. Bacteria in the gut perform many important functions for humans, including breaking down and aiding in the absorption of otherwise indigestible food; stimulating cell growth; repressing the growth of harmful bacteria, training the immune system to respond only to pathogens; producing vitamin B12, and defending against some infectious diseases.

Advice and guidance

Governmental policies

The updated USDA food pyramid, published in 2005, is a general nutrition guide for recommended food consumption for humans.

In the US, dietitians are registered (RD) or licensed (LD) with the Commission for Dietetic Registration and the American Dietetic Association, and are only able to use the title "dietitian," as described by the business and professions codes of each respective state, when they have met specific educational and experiential prerequisites and passed a national registration or licensure examination, respectively. In California, registered dietitions must abide by the "Business and Professions Code of Section 2585-2586.8". http://www.leginfo.ca.gov/cgi-bin/displaycode?section=bpc&group=02001-03000&file=2585-2586.8. Anyone may call themselves a nutritionist, including unqualified dietitions, as this term is unregulated. Some states, such as the State of Florida, have begun to include the title "nutritionist" in state licensure requirements. Most governments provide guidance on nutrition, and some also impose mandatory disclosure/labeling requirements for processed food manufacturers and restaurants to assist consumers in complying with such guidance.

In the US, nutritional standards and recommendations are established jointly by the US Department of Agriculture and US Department of Health and Human Services. Dietary and physical activity guidelines from the USDA are presented in the concept of a food pyramid, which superseded the Four Food Groups. The Senate committee currently responsible for oversight of the USDA is the Agriculture, Nutrition and Forestry Committee. Committee hearings are often televised on C-SPAN as seen here.

The U.S. Department of Health and Human Services provides a sample week-long menu which fulfills the nutritional recommendations of the government.^[19] Canada's Food Guide is another governmental recommendation.

Teaching

Nutrition is taught in schools in many countries. In England and Wales the Personal and Social Education and Food Technology curricula include nutrition, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging. In many schools a Nutrition class will fall within the Family and Consumer Science or Health departments. In some American schools, students are required to take a certain number of FCS or Health related classes. Nutrition is offered at many schools, and if it is not a class of its own, nutrition is included in other FCS or Health classes such as: Life Skills, Independent Living, Single Survival, Freshmen Connection, Health etc. In many Nutrition classes, students learn about the food groups, the food pyramid, Daily Recommended Allowances, calories, vitamins, minerals, malnutrition, physical activity, healthy food choices and how to live a healthy life.

A 1985 US National Research Council report entitled Nutrition Education in US Medical Schools concluded that nutrition education in medical schools was inadequate.^[20] Only 20% of the schools surveyed taught nutrition as a separate, required course. A 2006 survey found that this number had risen to 30%.^[21]

Healthy diets

Main article: Healthy diet

Whole plant food diet

Heart disease, cancer, obesity, and diabetes are commonly called "Western" diseases because these maladies were once rarely seen in developing countries. One study in China found some regions had essentially no cancer or heart disease, while in other areas they reflected "up to a 100-fold increase" coincident with diets that were found to be entirely plant-based to heavily animal-based, respectively.^[22] In contrast, diseases of affluence like cancer and heart disease are common throughout the United States. Adjusted for age and exercise, large regional clusters of people in China rarely suffered from these "Western" diseases possibly because their diets are rich in vegetables, fruits and whole grains.^[22]

The United Healthcare/Pacificare nutrition guideline recommends a whole plant food diet, and recommends using protein only as a condiment with meals. A National Geographic cover article from November, 2005, entitled The Secrets of Living Longer, also recommends a whole plant food diet. The article is a lifestyle survey of three populations, Sardinians, Okinawans, and Adventists, who generally display longevity and "suffer a fraction of the diseases that commonly kill people in other parts of the developed world, and enjoy more healthy years of life." In sum, they offer three sets of 'best practices' to emulate. The rest is up to you. In common with all three groups is to "Eat fruits, vegetables, and whole grains."

The National Geographic article noted that an NIH funded study of 34,000 Seventh-day Adventists between 1976 and 1988 "…found that the Adventists' habit of consuming beans, soy milk, tomatoes, and other fruits lowered their risk of developing certain cancers. It also suggested that eating whole grain bread, drinking five glasses of water a day, and, most surprisingly, consuming four servings of nuts a week reduced their risk of heart disease."

The French "paradox"

Main article: French paradox

It has been discovered that people living in France live longer. Even though they consume more saturated fats than Americans, the rate of heart disease is lower in France than in North America. A number of explanations have been suggested:

• Reduced consumption of processed carbohydrate and other junk foods.
• Regular consumption of red wine.
• More active lifestyles involving plenty of daily exercise, especially walking; the French are much less dependent on cars than Americans are.
• Higher consumption of artificially produced trans-fats by Americans, which has been shown to have greater lipoprotein effects per gram than saturated fat.^[23]

However, statistics collected by the World Health Organization from 1990-2000 show that the incidence of heart disease in France may have been underestimated and in fact be similar to that of neighboring countries.^[24]

Sports nutrition

Main article: Sports nutrition

Protein

Protein milkshakes, made from protein powder (center) and milk (left), are a common bodybuilding supplement.

Protein is an important component of every cell in the body. Hair and nails are mostly made of protein. The body uses protein to build and repair tissues. Also protein is used to make enzymes, hormones, and other body chemicals. Protein is an important building block of bones, muscles, cartilage, skin, and blood.

The protein requirement for each individual differs, as do opinions about whether and to what extent physically active people require more protein. The 2005 Recommended Dietary Allowances (RDA), aimed at the general healthy adult population, provide for an intake of 0.8 - 1 grams of protein per kilogram of body weight (according to the BMI formula), with the review panel stating that "no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise".^[25] Conversely, Di Pasquale (2008), citing recent studies, recommends a minimum protein intake of 2.2 g/kg "for anyone involved in competitive or intense recreational sports who wants to maximize lean body mass but does not wish to gain weight".^[26]

Water and salts

Water is one of the most important nutrients in the sports diet. It helps eliminate food waste products in the body, regulates body temperature during activity and helps with digestion. Maintaining hydration during periods of physical exertion is key to peak performance. While drinking too much water during activities can lead to physical discomfort, dehydration in excess of 2% of body mass (by weight) markedly hinders athletic performance. Additional carbohydrates and protein before, during, and after exercise increase time to exhaustion as well as speed recovery. Dosage is based on work performed, lean body mass, and environmental factors, especially ambient temperature and humidity. maintaining the right amount is key.

Carbohydrates

The main fuel used by the body during exercise is carbohydrates, which is stored in muscle as glycogen—a form of sugar. During exercise, muscle glycogen reserves can be used up, especially when activities last longer than 90 min.^{[citation needed]} Because the amount of glycogen stored in the body is limited, it is important for athletes to replace glycogen by consuming a diet high in carbohydrates. Meeting energy needs can help improve performance during the sport, as well as improve overall strength and endurance.

There are different kinds of carbohydrates—simple or refined, and unrefined. A typical American consumes about 50% of their carbohydrates as simple sugars, which are added to foods as opposed to sugars that come naturally in fruits and vegetables. These simple sugars come in large amounts in sodas and fast food. Over the course of a year, the average American consumes 54 gallons of soft drinks, which contain the highest amount of added sugars.^[27] Even though carbohydrates are necessary for humans to function, they are not all equally healthful. When machinery has been used to remove bits of high fiber, the carbohydrates are refined. These are the carbohydrates found in white bread and fast food.^[28]

Malnutrition

Main article: Malnutrition

Malnutrition refers to insufficient, excessive, or imbalanced consumption of nutrients. In developed countries, the diseases of malnutrition are most often associated with nutritional imbalances or excessive consumption. Although there are more people in the world who are malnourished due to excessive consumption, according to the United Nations World Health Organization, the real challenge in developing nations today, more than starvation, is combating insufficient nutrition — the lack of nutrients necessary for the growth and maintenance of vital functions.

Illnesses caused by improper nutrient consumption

Nutrients	Deficiency	Excess
Energy	Starvation, Marasmus	Obesity, diabetes mellitus, Cardiovascular disease
Simple carbohydrates	none	diabetes mellitus, Obesity
Complex carbohydrates	none	Obesity
Saturated fat	low sex hormone levels [29]	Cardiovascular disease (claimed by most doctors and nutritionists)
Trans fat	none	Cardiovascular Disease
Unsaturated fat	none	Obesity
Fat	Malabsorption of Fat-soluble vitamins, Rabbit Starvation (If protien intake is high)	Cardiovascular Disease (claimed by some)
Omega 3 Fats	Cardiovascular Disease	Bleeding, Hemorrhages
Omega 6 Fats	none	Cardiovascular Disease, Cancer
Cholesterol	none	Cardiovascular disease (claimed by many)
Protein	kwashiorkor	Rabbit starvation
Sodium	hyponatremia	Hypernatremia, hypertension
Iron	Anemia	Cirrhosis, heart disease
Iodine	Goiter, hypothyroidism	Iodine Toxicity (goiter, hypothyroidism)
Vitamin A	Xerophthalmia and Night Blindness, low testosterone levels	Hypervitaminosis A (cirrhosis, hair loss)
Vitamin B1	Beri-Beri
Vitamin B2	Cracking of skin and Corneal Unclearation
Niacin	Pellagra	dyspepsia, cardiac arrhythmias, birth defects
Vitamin B12	Pernicious Anemia
Vitamin C	Scurvy	diarrhea causing dehydration
Vitamin D	Rickets	Hypervitaminosis D (dehydration, vomiting, constipation)
Vitamin E	nervous disorders	Hypervitaminosis E (anticoagulant: excessive bleeding)
Vitamin K	Hemorrhage
Calcium	Osteoporosis, tetany, carpopedal spasm, laryngospasm, cardiac arrhythmias	Fatigue, depression, confusion, anorexia, nausea, vomiting, constipation, pancreatitis, increased urination
Magnesium	Hypertension	Weakness, nausea, vomiting, impaired breathing, and hypotension
Potassium	Hypokalemia, cardiac arrhythmias	Hyperkalemia, palpitations

Mental agility

Main article: Nootropic

Research indicates that improving the awareness of nutritious meal choices and establishing long-term habits of healthy eating has a positive effect on a cognitive and spatial memory capacity, potentially increasing a student's potential to process and retain academic information.

Some organizations have begun working with teachers, policymakers, and managed foodservice contractors to mandate improved nutritional content and increased nutritional resources in school cafeterias from primary to university level institutions. Health and nutrition have been proven to have close links with overall educational success.^[30] Currently less than 10% of American college students report that they eat the recommended five servings of fruit and vegetables daily.^[31] Better nutrition has been shown to have an impact on both cognitive and spatial memory performance; a study showed those with higher blood sugar levels performed better on certain memory tests.^[32] In another study, those who consumed yogurt performed better on thinking tasks when compared to those who consumed caffeine free diet soda or confections.^[33] Nutritional deficiencies have been shown to have a negative effect on learning behavior in mice as far back as 1951.^[34]

"Better learning performance is associated with diet induced effects on learning and memory ability".^[35]

The "nutrition-learning nexus" demonstrates the correlation between diet and learning and has application in a higher education setting.

"We find that better nourished children perform significantly better in school, partly because they enter school earlier and thus have more time to learn but mostly because of greater learning productivity per year of schooling."^[36]

91% of college students feel that they are in good health while only 7% eat their recommended daily allowance of fruits and vegetables.^[31]

Nutritional education is an effective and workable model in a higher education setting.^[37][38]

More "engaged" learning models that encompass nutrition is an idea that is picking up steam at all levels of the learning cycle.^[39]

There is limited research available that directly links a student's Grade Point Average (G.P.A.) to their overall nutritional health. Additional substantive data is needed to prove that overall intellectual health is closely linked to a person's diet, rather than just another correlation fallacy.

Mental disorders

Nutritional supplement treatment may be appropriate for major depression, bipolar disorder, schizophrenia, and obsessive compulsive disorder, the four most common mental disorders in developed countries.^[40]

Cancer

Cancer is now common in developing countries. According a study by the International Agency for Research on Cancer, "In the developing world, cancers of the liver, stomach and esophagus were more common, often linked to consumption of carcinogenic preserved foods, such as smoked or salted food, and parasitic infections that attack organs." Lung cancer rates are rising rapidly in poorer nations because of increased use of tobacco. Developed countries "tended to have cancers linked to affluence or a 'Western lifestyle' — cancers of the colon, rectum, breast and prostate — that can be caused by obesity, lack of exercise, diet and age."^[41]

Metabolic syndrome

Several lines of evidence indicate lifestyle-induced hyperinsulinemia and reduced insulin function (i.e. insulin resistance) as a decisive factor in many disease states. For example, hyperinsulinemia and insulin resistance are strongly linked to chronic inflammation, which in turn is strongly linked to a variety of adverse developments such as arterial microinjuries and clot formation (i.e. heart disease) and exaggerated cell division (i.e. cancer). Hyperinsulinemia and insulin resistance (the so-called metabolic syndrome) are characterized by a combination of abdominal obesity, elevated blood sugar, elevated blood pressure, elevated blood triglycerides, and reduced HDL cholesterol. The negative impact of hyperinsulinemia on prostaglandin PGE1/PGE2 balance may be significant.

The state of obesity clearly contributes to insulin resistance, which in turn can cause type 2 diabetes. Virtually all obese and most type 2 diabetic individuals have marked insulin resistance. Although the association between overweight and insulin resistance is clear, the exact (likely multifarious) causes of insulin resistance remain less clear. Importantly, it has been demonstrated that appropriate exercise, more regular food intake and reducing glycemic load (see below) all can reverse insulin resistance in overweight individuals (and thereby lower blood sugar levels in those who have type 2 diabetes).

Obesity can unfavourably alter hormonal and metabolic status via resistance to the hormone leptin, and a vicious cycle may occur in which insulin/leptin resistance and obesity aggravate one another. The vicious cycle is putatively fuelled by continuously high insulin/leptin stimulation and fat storage, as a result of high intake of strongly insulin/leptin stimulating foods and energy. Both insulin and leptin normally function as satiety signals to the hypothalamus in the brain; however, insulin/leptin resistance may reduce this signal and therefore allow continued overfeeding despite large body fat stores. In addition, reduced leptin signalling to the brain may reduce leptin's normal effect to maintain an appropriately high metabolic rate.

There is a debate about how and to what extent different dietary factors— such as intake of processed carbohydrates, total protein, fat, and carbohydrate intake, intake of saturated and trans fatty acids, and low intake of vitamins/minerals—contribute to the development of insulin and leptin resistance. In any case, analogous to the way modern man-made pollution may potentially overwhelm the environment's ability to maintain homeostasis, the recent explosive introduction of high glycemic index and processed foods into the human diet may potentially overwhelm the body's ability to maintain homeostasis and health (as evidenced by the metabolic syndrome epidemic).

Hyponatremia

Excess water intake, without replenishment of sodium and potassium salts, leads to hyponatremia, which can further lead to water intoxication at more dangerous levels. A well-publicized case occurred in 2007, when Jennifer Strange died while participating in a water-drinking contest.^[42] More usually, the condition occurs in long-distance endurance events (such as marathon or triathlon competition and training) and causes gradual mental dulling, headache, drowsiness, weakness, and confusion; extreme cases may result in coma, convulsions, and death. The primary damage comes from swelling of the brain, caused by increased osmosis as blood salinity decreases. Effective fluid replacement techniques include Water aid stations during running/cycling races, trainers providing water during team games such as Soccer and devices such as Camel Baks which can provide water for a person without making it too hard to drink the water.

Processed foods

Main article: Food processing

Since the Industrial Revolution some two hundred years ago, the food processing industry has invented many technologies that both help keep foods fresh longer and alter the fresh state of food as they appear in nature. Cooling is the primary technology used to maintain freshness, whereas many more technologies have been invented to allow foods to last longer without becoming spoiled. These latter technologies include pasteurisation, autoclavation, drying, salting, and separation of various components, and all appear to alter the original nutritional contents of food. Pasteurisation and autoclavation (heating techniques) have no doubt improved the safety of many common foods, preventing epidemics of bacterial infection. But some of the (new) food processing technologies undoubtedly have downfalls as well.

Modern separation techniques such as milling, centrifugation, and pressing have enabled concentration of particular components of food, yielding flour, oils, juices and so on, and even separate fatty acids, amino acids, vitamins, and minerals. Inevitably, such large scale concentration changes the nutritional content of food, saving certain nutrients while removing others. Heating techniques may also reduce food's content of many heat-labile nutrients such as certain vitamins and phytochemicals, and possibly other yet to be discovered substances.^[43] Because of reduced nutritional value, processed foods are often 'enriched' or 'fortified' with some of the most critical nutrients (usually certain vitamins) that were lost during processing. Nonetheless, processed foods tend to have an inferior nutritional profile compared to whole, fresh foods, regarding content of both sugar and high GI starches, potassium/sodium, vitamins, fiber, and of intact, unoxidized (essential) fatty acids. In addition, processed foods often contain potentially harmful substances such as oxidized fats and trans fatty acids.

A dramatic example of the effect of food processing on a population's health is the history of epidemics of beri-beri in people subsisting on polished rice. Removing the outer layer of rice by polishing it removes with it the essential vitamin thiamine, causing beri-beri. Another example is the development of scurvy among infants in the late 1800s in the United States. It turned out that the vast majority of sufferers were being fed milk that had been heat-treated (as suggested by Pasteur) to control bacterial disease. Pasteurisation was effective against bacteria, but it destroyed the vitamin C.

As mentioned, lifestyle- and obesity-related diseases are becoming increasingly prevalent all around the world. There is little doubt that the increasingly widespread application of some modern food processing technologies has contributed to this development. The food processing industry is a major part of modern economy, and as such it is influential in political decisions (e.g. nutritional recommendations, agricultural subsidising). In any known profit-driven economy, health considerations are hardly a priority; effective production of cheap foods with a long shelf-life is more the trend. In general, whole, fresh foods have a relatively short shelf-life and are less profitable to produce and sell than are more processed foods. Thus the consumer is left with the choice between more expensive but nutritionally superior whole, fresh foods, and cheap, usually nutritionally inferior processed foods. Because processed foods are often cheaper, more convenient (in both purchasing, storage, and preparation), and more available, the consumption of nutritionally inferior foods has been increasing throughout the world along with many nutrition-related health complications.

History

Humans have evolved as omnivorous hunter-gatherers over the past 250,000 years. The diet of early modern humans varied significantly depending on location and climate. The diet in the tropics tended to be based more heavily on plant foods, while the diet at higher latitudes tended more towards animal products. Analysis of postcranial and cranial remains of humans and animals from the Neolithic, along with detailed bone modification studies have shown that cannibalism was also prevalent among prehistoric humans.^[44]

Agriculture developed about 10,000 years ago in multiple locations throughout the world, providing grains such as wheat, rice, and maize, with staples such as bread and pasta. Farming also provided milk and dairy products, and sharply increased the availability of meats and the diversity of vegetables. The importance of food purity was recognized when bulk storage led to infestation and contamination risks. Cooking developed as an often ritualistic activity, due to efficiency and reliability concerns requiring adherence to strict recipes and procedures, and in response to demands for food purity and consistency.^[45]

From antiquity to 1900

The first recorded nutritional experiment is found in the Bible's Book of Daniel. Daniel and his friends were captured by the king of Babylon during an invasion of Israel. Selected as court servants, they were to share in the king's fine foods and wine. But they objected, preferring vegetables (pulses) and water in accordance with their Jewish dietary restrictions. The king's chief steward reluctantly agreed to a trial. Daniel and his friends received their diet for 10 days and were then compared to the king's men. Appearing healthier, they were allowed to continue with their diet.^[46]

Anaxagoras

Around 475 BC, Anaxagoras stated that food is absorbed by the human body and therefore contained "homeomerics" (generative components), suggesting the existence of nutrients.^[45] Around 400 BC, Hippocrates said, "Let food be your medicine and medicine be your food."^[47]

In the 1500s, scientist and artist Leonardo da Vinci compared metabolism to a burning candle. In 1747, Dr. James Lind, a physician in the British navy, performed the first scientific nutrition experiment, discovering that lime juice saved sailors who had been at sea for years from scurvy, a deadly and painful bleeding disorder. The discovery was ignored for forty years, after which British sailors became known as "limeys." The essential vitamin C within lime juice would not be identified by scientists until the 1930s.

Around 1770, Antoine Lavoisier, the "Father of Nutrition and Chemistry" discovered the details of metabolism, demonstrating that the oxidation of food is the source of body heat. In 1790, George Fordyce recognized calcium as necessary for fowl survival. In the early 1800s, the elements carbon, nitrogen, hydrogen and oxygen were recognized as the primary components of food, and methods to measure their proportions were developed.

In 1816, François Magendie discovered that dogs fed only carbohydrates and fat lost their body protein and died in a few weeks, but dogs also fed protein survived, identifying protein as an essential dietary component. In 1840, Justus Liebig discovered the chemical makeup of carbohydrates (sugars), fats (fatty acids) and proteins (amino acids.) In the 1860s, Claude Bernard discovered that body fat can be synthesized from carbohydrate and protein, showing that the energy in blood glucose can be stored as fat or as glycogen.

In the early 1880s, Kanehiro Takaki observed that Japanese sailors (whose diets consisted almost entirely of white rice) developed beriberi (or endemic neuritis, a disease causing heart problems and paralysis) but British sailors and Japanese naval officers did not. Adding various types of vegetables and meats to the diets of Japanese sailors prevented the disease.

In 1896, Baumann observed iodine in thyroid glands. In 1897, Christiaan Eijkman worked with natives of Java, who also suffered from beriberi. Eijkman observed that chickens fed the native diet of white rice developed the symptoms of beriberi, but remained healthy when fed unprocessed brown rice with the outer bran intact. Eijkman cured the natives by feeding them brown rice, discovering that food can cure disease. Over two decades later, nutritionists learned that the outer rice bran contains vitamin B1, also known as thiamine.

From 1900 to the present

In the early 1900s, Carl Von Voit and Max Rubner independently measured caloric energy expenditure in different species of animals, applying principles of physics in nutrition. In 1906, Wilcock and Hopkins showed that the amino acid tryptophan was necessary for the survival of rats. He fed them a special mixture of food containing all the nutrients he believed were essential for survival, but the rats died. A second group of rats to which he also fed fed an amount of milk containing vitamins.^[48] Gowland Hopkins recognized "accessory food factors" other than calories, protein and minerals, as organic materials essential to health but which the body cannot synthesize. In 1907, Stephen M. Babcock and Edwin B. Hart conducted the single-grain experiment. This experiment runs through 1911.

In 1912, Casimir Funk coined the term vitamin, a vital factor in the diet, from the words "vital" and "amine," because these unknown substances preventing scurvy, beriberi, and pellagra, were thought then to be derived from ammonia. The vitamins were studied in the first half of the twentieth century.

In 1913, Elmer McCollum discovered the first vitamins, fat soluble vitamin A, and water soluble vitamin B (in 1915; now known to be a complex of several water-soluble vitamins) and names vitamin C as the then-unknown substance preventing scurvy. Lafayette Mendel and Thomas Osborne also perform pioneering work on vitamin A and B. In 1919, Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency, because he could cure it in dogs with cod liver oil.^[49] In 1922, McCollum destroyed the vitamin A in cod liver oil but finds it still cures rickets, naming vitamin D Also in 1922, H.M. Evans and L.S. Bishop discover vitamin E as essential for rat pregnancy, originally calling it "food factor X" until 1925.

In 1925, Hart discovered that trace amounts of copper are necessary for iron absorption. In 1927, Adolf Otto Reinhold Windaus synthesized vitamin D, for which he won the Nobel Prize in Chemistry in 1928. In 1928, Albert Szent-Györgyi isolated ascorbic acid, and in 1932 proves that it is vitamin C by preventing scurvy. In 1935 he synthesizes it, and in 1937 he wins a Nobel Prize for his efforts. Szent-Györgyi concurrently elucidates much of the citric acid cycle.

In the 1930s, William Cumming Rose identified essential amino acids, necessary protein components which the body cannot synthesize. In 1935, Underwood and Marston independently discover the necessity of cobalt. In 1936, Eugene Floyd Dubois showed that work and school performance are related to caloric intake. In 1938, Erhard Fernholz discovered the chemical structure of vitamin E. It was synthesised by Paul Karrer.

In 1940, rationing in the United Kingdom during and after World War II took place according to nutritional principles drawn up by Elsie Widdowson and others. In 1941, the first Recommended Dietary Allowances (RDAs) were established by the National Research Council.

In 1992, The U.S. Department of Agriculture introduced the Food Guide Pyramid. In 2002, a Natural Justice study showed a relation between nutrition and violent behavior. In 2005, a study found that obesity may be caused by adenovirus in addition to bad nutrition.^[50]

See also

Food portal

Main list: List of basic nutrition topics

Balanced Eating: Food Balance Wheel Biology: Digestion Enzyme Dangers of poor nutrition Deficiency Avitaminosis is a deficiency of vitamins. Boron deficiency (medicine) Chromium deficiency Iron deficiency (medicine) Iodine deficiency Magnesium deficiency (medicine) Diabetes Eating disorders Illnesses related to poor nutrition Malnutrition Obesity Childhood obesity Starvation Food: Food (portal) 5 A Day Canada's Food Guide Fast Food Food groups Food guide pyramid Food supplements Fruits Functional food Grains Junk Food Meat Vegetables

Healthy diet: Dieting Eating Healthy eating pyramid Nutritional rating systems Physicians Committee for Responsible Medicine (PCRM) The China Study Lists: Diets (list) List of food additives List of illnesses related to poor nutrition List of life extension related topics List of publications in nutrition List of unrefined sweeteners List of antioxidants List of phytochemicals Nutrients: Carbohydrates Dietary minerals Essential minerals Dietary supplements Evolution of dietary antioxidants Essential nutrients Fat Essential fatty acids Macronutrients Micronutrients Nootropics Nutraceuticals Food fortification

Phytochemicals Protein Complete protein Essential amino acids Incomplete protein Protein combining Protein in nutrition Vitamins Megavitamin therapy Vitamin C megadosage Profession: Dietitian Nutritionist Food Studies Tools: Nutrition scale Organizations: American Dietetic Association American Society for Nutrition British Dietetic Association Related topics Main article: Health Auxology Exercise General Fitness Training Health (portal) Life extension Orthomolecular medicine Physical fitness

Further reading

• Curley, S., and Mark (1990). The Natural Guide to Good Health, Lafayette, Louisiana, Supreme Publishing
• Galdston, I. (1960). Human Nutrition Historic and Scientific. New York: International Universities Press. 
• Mahan, L.K. and Escott-Stump, S. eds. (2000). Krause's Food, Nutrition, and Diet Therapy (10th ed.). Philadelphia: W.B. Saunders Harcourt Brace. ISBN 0721679048. 
• Thiollet, J.-P. (2001). Vitamines & minéraux. Paris: Anagramme. 
• Walter C. Willett and Meir J. Stampfer (January 2003). "Rebuilding the Food Pyramid". Scientific American 288 (1): 64–71. PMID 12506426. 

References

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43. ^ Morris, Audrey; Audia Barnett, Olive-Jean Burrows (2004). "Effect of Processing on Nutrient Content of Foods" (PDF). Cajanus 37 (3): 160–164. http://www.paho.org/English/CFNI/cfni-caj37No304-art-3.pdf. Retrieved on 2006-10-26. 
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48. ^ Heinemann 2e Biology Activity Manual by Judith Brotherton and Kate Mundie
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50. ^ "Can a virus make you fat?" at BBC News; "Contagious obesity? Identifying the human adenoviruses that may make us fat" at Science Blog

External links

• Nutrition assessment and consultation advanced online nutrition information and services
• Diet, Nutrition and the prevention of chronic diseases by a Joint WHO/FAO Expert consultation (2003)
• United States Department of Agriculture (USDA) Frequently asked questions
• Nutrition Facts and Foods Source of Nutrients, based on USDA National Nutrient Database Release 21, Complete Nutrients Version
• Nutritional Status Assessment and Analysis - e-learning from FAO
• International Organization of Nutritional Consultants
• Mother, Infant and Young Child Nutrition & Malnutrition Optimal maternal, infant and young child feeding and caring practices
• Q.O.A.C.H - nutrition Question-coaching for better nutrition
• Nutrition-chart, mineral contents, vitamins details, fruit chart, vegetable chart
• UN Standing Committee on Nutrition - In English, French and Portuguese

Databases and search engines

• Nutrition Data
• German Nutrition Data with fast search on www.lexolino.de
• USDA National Nutrient Database for Standard Reference Search By Food
• USDA National Nutrient Database for Standard Reference Nutrient Lists Search By Nutrient

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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - ernæring

Nederlands (Dutch)
voeding, voedingswaarde/ -leer

Français (French)
n. - nutrition, alimentation, diététique

Deutsch (German)
n. - Ernährung, Nahrung

Ελληνική (Greek)
n. - θρέψη, διατροφή

Italiano (Italian)
nutrizione

Português (Portuguese)
n. - nutrição (f)

Русский (Russian)
питание

Español (Spanish)
n. - alimentación, nutrición

Svenska (Swedish)
n. - näringsprocess, näring, näringstillförsel, näringslära

中文（简体）(Chinese (Simplified))
营养, 营养学

中文（繁體）(Chinese (Traditional))
n. - 營養, 營養學

한국어 (Korean)
n. - 영양학, 영양물 섭취

日本語 (Japanese)
n. - 栄養の摂取, 栄養物, 栄養学

العربيه (Arabic)
‏(الاسم) تغذيه‏

עברית (Hebrew)
n. - ‮תזונה, הזנה, אוכל, מזון, חקר המזונות המבריאים‬

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