essential fatty acid

(biochemistry) Any of the polyunsaturated fatty acids which are required in the diet of mammals; they are probably precursors of prostaglandins.

Two polyunsaturated fatty acids cannot be made in the body and are therefore dietary essentials: linoleic (C18 : 2 ω6) and α-linolenic (C18 : 3 ω3). Several other fatty acids have some EFA activity in that they cure some, but not all, of the signs of (experimental) EFA deficiency. Arachidonic, eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids are physiologically important, although they are not dietary essentials since they can be formed from linoleic and α-linolenic acids.

The requirement to prevent deficiency is about 1% of total energy intake, equivalent to 260 mg/MJ; a desirable intake, and the basis of Reference Intakes is 8-10% of energy intake, about 2-2.6 g/MJ. Although all fatty foods contain some essential fatty acids, the richest sources are vegetable and fish oils.

An unsaturated fatty acid, such as linoleic acid, that is required for normal, healthy functioning of the body. Essential fatty acids cannot be made in the body; they must be obtained from foods such as nuts, oilseeds and their products (e.g. sunflower oil and other vegetable oils), and oil-rich fish. They are used as the raw material for several compounds, such as prostaglandins and leukotrienes, which help to control blood pressure and other vital bodily activities. Lack of essential fatty acid may result in hyperactivity, reduced growth, and even death.

Description

Essential fatty acids (EFAs) are fats that are essential to the diet because the body cannot produce them. Essential fatty acids are extremely important nutrients for health. They are present in every healthy cell in the body, and are critical for the normal growth and functioning of the cells, muscles, nerves, and organs. EFAs are also used by the body to produce a class of hormone-like substances called prostaglandins, which are key to many important processes. Deficiencies of EFAs are linked to a variety of health problems, including major ones such as heart disease, cancer, and diabetes. It has been estimated that as many as 80% of American people may consume insufficient quantities of EFAs.

Very few health issues have received as much attention during the past several decades as the question of fat in the diet. Sixty-eight percent of deaths in America are related to fat consumption and diet, including heart disease (44% of deaths), cancer (22%) and diabetes (2%). There are several types of dietary fats. Saturated fat is found mainly in animal products, including meat and dairy products, and avocados, and nuts. Cholesterol is a dietary fat that is only found in animal products. Cholesterol is also made by the body in small amounts from saturated fats. Heavy consumption of saturated fat and cholesterol has been linked to heart disease and cancer. Unsaturated fats are typically oils from vegetables, nuts, and are present in some fish. These are considered the healthiest dietary fats. Essential fatty acids are unsaturated fats. EFAs are the only fats that may need to be increased in the American diet.

Scientists classify essential fatty acids into two types, omega-3 fatty acids and omega-6 fatty acids, depending on their chemical composition. Technically, the omega-3 fatty acids are alpha-linolenic acid, stearidonic acid, and two others called EPA and DHA. Alpha-linolenic acid is found mainly in flaxseed oil, canola oil, soybeans, walnuts, hemp seeds, and dark green leafy vegetables. Stearidonic acid is found in rarer types of seeds and nuts, including black currant seeds. EPA and DHA are present in cold-water fish, including salmon, trout, sardines, mackerel, and cod. Cod liver oil is a popular nutritional supplement for omega-3 EFAs.

Omega-6 fatty acids are more common in the American diet than the omega-3 EFAs. These include linoleic acid, which is found in safflower, olive, almond, sunflower, hemp, soybean, walnut, pumpkin, sesame, and flaxseed oils. Gamma-linolenic acid (GLA) is found in some seeds and evening primrose oil. Arachidonic acid (AA) is present in meat and animal products.

Both types of EFAs, omega-3 and omega-6 fatty acids, are necessary in a healthy diet. Deficiencies of EFAs have been brought about by changes in diet and the modern processing of foods and oils. Many nutritionists believe that a major dietary problem is the use of hydrogenated oils, which are present in margarine and many processed foods. Hydrogenated oils are highly refined by industrial processes, and contain toxic by-products and trans-fatty acids. Trans-fatty acids are fat molecules with chemically altered structures, and are believed to have several detrimental effects on the body. Transfatty acids interfere with the absorption of healthy EFAs, and may contribute to atherosclerosis, or damage to the arteries. Deep-fried foods, which are cooked in oil that is altered by very high temperatures, also contain transfatty acids. Many health professionals, including those at the World Heath Organization, have protested against the use of hydrogenated oils in food and the consumption of trans-fatty acids. Health conditions linked to the consumption of trans-fatty acids and hydrogenated oils include cancer, heart disease, high cholesterol, diabetes, obesity, immune system disorders, decreased sperm counts, and infant development problems.

Dietary changes that have contributed to EFA deficiency or imbalances include the increased use of oils that contain few or no omega-3 EFAs; the industrial milling of flour that removes the EFA-containing germ; the increase of sugar and fried foods in the diet that may interfere with the body's absorption of EFAs; and the decreased consumption of fish.

A balance of omega-3 and omega-6 EFAs in the diet is recommended by experts. Americans typically consume higher quantities of omega-6 EFAs, because these are found in meat, animal products, and common cooking oils. Research has shown that too many omega-6 EFAs in the diet can lead to the imbalanced production of prostaglandins, which may contribute to health problems. Experts recommend that omega-3 and omega-6 EFAs be present in the diet in a ratio of around one to three. Americans consume a ratio as high as one to 40. Thus, the need for greater amounts of omega-3 EFAs in the diet has increased.

Symptoms of EFA deficiency or imbalance include dry or scaly skin, excessively dry hair, cracked fingernails, fatigue, weakness, frequent infections, allergies, mood disorders, hyperactivity, depression, memory and learning problems, slow wound healing, aching joints, poor digestion, high blood pressure, obesity, and high cholesterol.

General Use

EFA supplementation is recommended for more than 60 health conditions. EFAs are used therapeutically to treat and prevent cardiovascular problems, including heart disease, high cholesterol, strokes, and high blood pressure. EFAs also have anti-inflammatory effects in the body, and are used in the nutritional treatment of arthritis, asthma, allergies, and skin conditions (e.g., eczema). EFAs are used as support for immune system disorders including AIDS, multiple sclerosis, lupus, and cancer.

Other conditions that may improve with EFA supplementation include acne and other skin problems, diabetes, depression, menopausal problems, nervous conditions, obesity, memory and learning disabilities, eye problems, and digestive disorders. EFAs are recommended for weight loss programs, as they may assist fat metabolism in the body. EFA supplementation is a recommended preventative practice, as well.

Preparations

Common EFA supplements are flaxseed oil, evening primrose oil, borage oil, black currant seed oil, hemp seed oil, and cod liver oil. Consumers should search for supplements that contain both omega-3 and omega-6 EFAs, because imbalances of EFAs may occur if either is taken in excess over long periods of time. Flaxseed oil is a recommended supplement, because it contains the highest percentage of omega-3 fatty acids with some omega-6 EFAs, as well. Flaxseed oil is generally the least expensive source of omega-3 EFAs as well, generally much cheaper than fish oil supplements. Evening primrose oil is a popular supplement as well, because the GLA it contains has shown benefits in treating premenstrual syndrome and other conditions. However, evening primrose oil contains no omega-3 EFAs. Hemp seed oil is a well-balanced source of both EFAs.

Supplements are available from health food stores in liquid and capsule form. The recommended daily dosage is one to two tablespoons (13-26 capsules), taken with meals. EFAs can also be obtained from a diet that includes cold-water fish consumed twice per week, whole grains, dark green leafy vegetables, walnuts, pumpkin seeds, wheat germ, soy products, canola oil, and other foods mentioned above. Whole flaxseeds are a wholesome source of EFAs as well, and can be freshly ground and added to salads and other dishes. Supplements that contain the enzyme lipase help the body more efficiently digest the oils.

Precautions

EFA supplements are generally fragile products, and must be produced, packaged and handled properly. Consumers should search for quality EFA supplements produced by reputable manufacturers. Products that are organically grown and certified by a third party are recommended. EFA products should be produced by "cold or modified expeller pressing," which means that they were produced without damaging temperatures or pressure. Products should be packaged in light-resistant containers, because sunlight damages EFAs. Packages should include manufacturing and expiration dates, in order to assure freshness. Stores and consumers should keep EFA products under refrigeration, because heat damages them. Taste can indicate the quality of EFA oils: those that have no flavor usually are overly refined, and those that taste bitter are old or spoiled. Because of their low temperature threshold, nearly all oils that are used as EFA supplements are not suitable for use as cooking oils.

In 2001, The U.S. Food and Drug Administration (FDA) began cautioning pregnant and nursing women and parents of infants and toddlers about the potential dangers of exposure to mercury from fish rich in omega-3 fatty acids, and from fish oil capsules. High levels of mercury can affect brain development in fetuses and young children. The FDA recommends that these groups instead opt for younger species of fish such as canned tuna or farm-raised fish and skip fish oil capsules altogether. Vegetarians can supplement their diets with foods high in aplah-linoleic acids, including certain oils, flaxseed, and walnuts.

Side Effects

Side effects with most EFA supplements are rare, because EFAs are nontoxic and are used by the body as energy when taken in excess. The exception is cod liver and fish oil supplements, which can cause vitamin A and D toxicity when taken in excess. Side effects of vitamin A and D toxicity include headaches, skin discoloration, fatigue, nausea, and gastrointestinal problems. Fish oil supplements that have vitamins A and D removed are available.

Interactions

To maximize the benefits of EFA supplements, several recommendations can be followed. EFA users should reduce the amount of fat, particularly saturated fat from animal products, in their diet. The American Heart Association recommends that a healthy diet contains 30% or less of its total calories from fat. For 2000 total calories per day, 600 calories or less should be from fat, including EFA supplements. Consumers should also completely eliminate hydrogenated and partially hydrogenated oils from their diets. This includes eliminating all processed foods that contain them, such as margarine and many packaged foods. Other foods that contain trans-fatty acids, such as deep fried foods, should also be eliminated. Recommended cooking oils are olive, safflower, canola, and sesame oils. EFA effectiveness may be increased by lowering the intake of sugar and alcohol in the diet. Nutrients that assist EFA uptake are the B-complex vitamins, vitamin C, zinc, and magnesium. As with any supplement, EFA effectiveness can be augmented with a nutritious, high fiber diet that emphasizes fresh and natural foods, and the intake of fish two times a week.

Resources

Books

Barilla, Jean. The Nutrition Superbook: The Good Fats and Oils. New Canaan, CT: Keats, 1996.

Erasmus, Udo. Fats That Heal, Fats That Kill. Burnaby, Canada: Alive Books, 1993.

Finnegan, John. The Facts about Fats. Berkeley: Celestial Arts, 1993.

Rudin, Dr. Donald O. and Clara Felix. The Omega-3 Phenomenon. New York: Rawson, 1987.

Schmidt, Michael. Smart Fats. Berkeley: Frog Press, 1997.

Periodicals

"Getting Omega–3 Without the Mercury." Nutrition Today (July-August 2002): 142.

"Oil–in–One." Better Nutrition (September 2002).

Organizations

Northwest Academy of Preventative Medicine. 15615 Bellevue-Redmond Road, Bellevue, WA 98008. (206) 881-9660.

Nutrition Health Review. 171 Madison Avenue, New York, NY 10016.

Nutrition Science News. 1401 Pearl Street, Boulder, CO 80302. (303) 939-8440.

Omega Nutrition. 720 East Washington St., Sequim, WA 98382. (800) 745-8580.

[Article by: Douglas Dupler; Teresa G. Odle]

An unsaturated fatty acid, such as linoleic acid, needed for normal, healthy functioning of the body, but which cannot be synthesized by the body. Lack of essential fatty acid may result in hyperactivity, reduced growth, and even death.

Types of Fats in Food
Unsaturated fat Monounsaturated fat Polyunsaturated fat Trans fat Omega: 3, 6, 9 Saturated fat Interesterified fat
See Also
Fatty acid Essential fatty acid

Essential fatty acids, or EFAs, are fatty acids that cannot be constructed within an organism from other components (generally all references are to humans) by any known chemical pathways; and therefore must be obtained from the diet. The term refers to those involved in biological processes, and not fatty acids which may just play a role as fuel. As many of the compounds created from essential fatty acids can be taken directly in the diet, it is possible that the amounts required in the diet (if any) are overestimated. It is also possible they can be underestimated as organisms can still survive in unideal, malnourished conditions.

There are two families of EFAs: ω-3 (or omega-3 or n-3) and ω-6 (omega-6, n-6.) Fats from each of these families are essential, as the body can convert one omega-3 to another omega-3, for example, but cannot create an omega-3 from scratch. They were originally designated as Vitamin F when they were discovered as essential nutrients in 1923. In 1930, work by Burr, Burr and Miller showed that they are better classified with the fats than with the vitamins.^[1]

Functions

The biological effects of the ω-3 and ω-6 fatty acids are largely mediated by their mutual interactions, see Essential fatty acid interactions for detail.

In the body, essential fatty acids serve multiple functions. In each of these, the balance between dietary ω-3 and ω-6 strongly affects function

• They are modified to make
  • the eicosanoids (affecting inflammation and many other cellular functions)
  • the endogenous cannabinoids (affecting mood, behavior and inflammation)
  • the lipoxins from ω-6 EFAs and resolvins from ω-3 (in the presence of aspirin, downregulating inflammation.)
  • the isofurans, neurofurans, isoprostanes, hepoxilins, epoxyeicosatrienoic acids (EETs) and Neuroprotectin D
• They form lipid rafts (affecting cellular signaling)^[2]
• They act on DNA (activating or inhibiting transcription factors such as NFκB, which is linked to pro-inflammatory cytokine production ) ^[3]

Nomenclature and terminology

Fatty acids are straight chain hydrocarbons possessing a carboxyl (COOH) group at one end. The carbon next to the carboxylate is known as α, the next carbon β, and so forth. Since biological fatty acids can be of different lengths, the last position is labelled ω, the last letter in the Greek alphabet. Since the physiological properties of unsaturated fatty acids largely depend on the position of the first unsaturation relative to the end position and not the carboxylate, the position is signified by (ω minus n). For example, the term ω-3 signifies that the first double bond exists as the third carbon-carbon bond from the terminal CH₃ end (ω) of the carbon chain. The number of carbons and the number of double bonds is also listed. ω-3 18:4 (stearidonic acid) or 18:4 ω-3 or 18:4 n-3 indicates an 18-carbon chain with 4 double bonds, and with the first double bond in the third position from the CH₃ end. Double bonds are cis and separated by a single methylene (CH₂) group unless otherwise noted. So in free fatty acid form, the chemical structure of stearidonic acid is:

Chemical structure of stearidonic acid showing physiological (red) and chemical (blue) numbering conventions.

Examples

For a complete tables of ω-3 and ω-6 essential fatty acids, see Polyunsaturated fatty acids.

The essential fatty acids start with the short chain polyunsaturated fatty acids (SC-PUFA):

• α-Linolenic acid (18:3) - ω-3
• Linoleic acid (18:2) - ω-6

These two fatty acids cannot be synthesised by humans, as humans lack the desaturase enzymes required for their production. They form the starting point for the creation of longer and more desaturated fatty acids, which are also referred to as long-chain polyunsaturated fatty acids (LC-PUFA):

• ω-3 fatty acids:
  • eicosapentaenoic acid or EPA (20:5)
  • docosahexaenoic acid or DHA (22:6)
• ω-6 fatty acids:
  • gamma-linolenic acid or GLA (18:3)
  • dihomo-gamma-linolenic acid or DGLA (20:3)
  • arachidonic acid or AA (20:4)

ω-9 fatty acids are not essential in humans, because humans possess all the enzymes required for their synthesis. The public is sometimes perceived as ignorant of this, as many supplement companies market Omega 3-6-9 blends.

What is "essential"?

Between 1930 and 1950, arachidonic acid and linolenic acid were termed 'essential' because each was more or less able to meet the growth requirements of rats given fat-free diets. Further research has shown that human metabolism requires both ω-3 and ω-6 fatty acids. To some extent, any ω-3 and any ω-6 can relieve the worst symptoms of fatty acid deficiency. Particular fatty acids are still needed at critical life stages (e.g. lactation) and in some disease states. See (Cunnane 2003)^[4] for a discussion of the current status of the term 'essential'. In scientific writing, common usage is that the term essential fatty acid comprises all the ω-3 or -6 fatty acids.^[5] Authoritative sources include the whole families, without qualification.^{[6] [7] [8]} The human body can make some long-chain PUFA (arachidonic acid, EPA and DHA) from lineolate or lineolinate.

Some writers therefore hold that the LC-PUFA are not essential, but that is not how the field has generally used the term.

Biologist Ray Peat, PhD, has pointed out flaws in the studies purportedly showing the need for n-3 and n-6 fats. He notes that so-called EFA deficiencies have been reversed by adding B vitamins or a fat-free liver extract to the diet. In his view, 'the optional dietary level of the "essential fatty acids" might be close to zero, if other dietary factors were also optimized.' [1]

Essential fatty acids should not be confused with essential oils, which are "essential" in the sense of being a concentrated essence.

Food sources

Almost all the polyunsaturated fat in the human diet is from EFA. Some of the food sources of ω-3 and ω-6 fatty acids are fish and shellfish, flaxseed (linseed), hemp oil, soya oil, canola (rapeseed) oil, chia seeds, pumpkin seeds, sunflower seeds, leafy vegetables, and walnuts.

Essential fatty acids play a part in many metabolic processes, and there is evidence to suggest that low levels of essential fatty acids, or the wrong balance of types among the essential fatty acids, may be a factor in a number of illnesses.

Plant sources of ω-3 do not contain eicosapentaenoic acid and docosahexaenoic acid. This is thought to be the reason that absorption of essential fatty acids is much greater from animal rather than plant sources (see Fish and plants as a source of Omega-3 for more).

The IUPAC Lipid HandbookPDF (370 KiB) provides a very large and detailed listing of fat contents of animal and vegetable fats, including ω-3 and -6 oils. The National Institutes of Health's EFA Education group publishes 'Essential Fats in Food Oils.' This lists 40 common oils, more tightly focused on EFAs and sorted by n-6:3 ratio. Stuchlik and Zak, 'Vegetable Lipids as Components of Functional Food'PDF (139 KiB) list notable vegetable sources of EFAs as well as commentary and an overview of the biosynthetic pathways involved. Users can interactively search at Nutrition Data for the richest food sources of particular EFAs or other nutrients. Careful readers will note that these sources are not in excellent agreement. EFA content of vegetable sources varies with cultivation conditions. Animal sources vary widely, both with the animal's feed and that the EFA makeup varies markedly with fats from different body parts.

Role in human health

For discussion how essential fatty acids affect cardiovascular health, see Diet and heart disease.

Almost all the polyunsaturated fats in the human diet are EFAs. Essential fatty acids play an important role in the life and death of cardiac cells.^{[9] [10] [11] [12]}

See also

• Polyunsaturated fat
• Omega-3 fatty acids
• Omega-6 fatty acids
• Essential fatty acid interactions
• Eicosanoid
  • Prostaglandin
  • Leukotriene
  • Thromboxane
• Endogenous Cannabinoid
• Essential nutrient
• Essential amino acids
• Fatty acid metabolism
• Fatty acid synthase
• Oily fish

References

1. ^ Burr, G.O., Burr, M.M. and Miller, E. (1930). "On the nature and role of the fatty acids essential in nutrition". J. Biol. Chem. 86 (587). Retrieved on 2007-01-17. 
2. ^ Stillwell W, Shaikh SR, Zerouga M, Siddiqui R, Wassall SR (2005). "Docosahexaenoic acid affects cell signaling by altering lipid rafts". REPRODUCTION, NUTRITION, DEVELOPMENT 45 (5): 559-579. PMID 16188208. 
3. ^ Calder PC (2004). "n-3 fatty acids, inflammation, and immunity--relevance to postsurgical and critically ill patients". LIPIDS 39 (12): 1147-1161. PMID 15736910. 
4. ^ Cunnane SC (2003). "Problems with essential fatty acids: time for a new paradigm?". PROGRESS IN LIPID RESEARCH 42 (6): 544-568. PMID 14559071. 
5. ^ Or at least the polyunsaturated, straight-chain methylene-interrupted ones; conjugated fatty acids like calendic acid are not.
6. ^ Heather Hutchins, MS, RD (10/19/2005). Symposium Highlights -- Omega-3 Fatty Acids: Recommendations for Therapeutics and Prevention.
   • "Omega-3 fatty acids and their counterparts, n-6 fatty acids, are essential polyunsaturated fatty acids (PUFA) because they cannot be synthesized de novo in the body."
7. ^ Nugent K, Spigelman A, Phillips R (1996). "Tissue prostaglandin levels in familial adenomatous polyposis patients treated with sulindac". Dis Colon Rectum 39 (6): 659-62. PMID 8646953. 
   • "Arachidonic acid is an essential fatty acid..."
8. ^ Carlstedt-Duke J, Brönnegård M, Strandvik B (1986). "Pathological regulation of arachidonic acid release in cystic fibrosis: the putative basic defect". Proc Natl Acad Sci U S A 83 (23): 9202-6. PMID 3097647. 
   • "[T]he turnover of essential fatty acids is increased (7). Arachidonic acid is one of the essential fatty acids affected."
9. ^ "External blockade...by polyunsaturated fatty acids". PMID 43279. Retrieved on 2007-01-18.  - see page 1 of this link
10. ^ "Antiarrythmic effects of omega-3 fatty acids". PMID 16919517. Retrieved on 2007-01-18. 
11. ^ "Alpha-linolenic acid, cardiovascular disease and sudden death". PMID 17086218. Retrieved on 2007-01-18. 
12. ^ "Omega-3 and health". PMID 17091903. Retrieved on 2007-01-18. 

• A.E. Hansen et al (1963). "Role of linoleic acid in infant nutrition". Pediatrics 31:171

External links

• Fats You Need -- Essential Fatty Acids
• USDA (public domain resource, and a source for this article)
• Cunnane Stephen C (June, 2005). Essential Fatty Acids: Time for a New Paradigm?. PUFA Newsletter. Retrieved on 2006-03-14.
• Stillwell W, Wassall SR.. Docosahexaenoic acid: membrane properties of a unique fatty acid.. Retrieved on February 8, 2006. Chem Phys Lipids. 2003 Nov;126(1):1-27

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