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-)

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)

Bibliog