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Omega-6 fatty acids are one of two groups of essential fatty acids (EFAs) that are required in human nutrition. (The other is the omega-3 fatty acid group.) Omega-6 fatty acids include linoleic acid and its derivatives. Essential means that these fatty acids must be consumed in the diet because humans cannot manufacture them from other dietary fats or nutrients, nor can they be stored in the body. They must be consumed daily to meet the body's requirements. They are macronutrients, required in amounts of grams per day (compared to micronutrients such as vitamins, which are required in milligrams per day). EFAs provide energy and are also components of nerve cells, cellular membranes, and are converted to hormone-like substances known as prostaglandins.
In the body, prostaglandins and EFAs are necessary for normal physiology, including:
EFAs are therapeutic, and clinical trials have shown that EFAs protect against such conditions as heart disease; cancer; autoimmune diseases, including rheumatoid arthritis and multiple sclerosis; skin diseases, including acne, atopic eczema, and psoriasis; and may protect against stroke. The prevalence of heart disease in populations has been shown to be inversely proportional to the relative concentration of linoleic acid in the diet.
Both linoleic acid and its derivatives are obtained from plant and animal sources. Plant sources include unprocessed, unheated vegetable oils such as corn, sunflower seed, safflower, soy, sesame, and cottonseed oils. They are also found in plant materials such as evening primrose, black currant seeds, and gooseberry oils as well as in raw nuts and seeds, legumes, and leafy greens. Animal sources of omega-6 fatty acids (although in smaller amounts than in plants) are lean meats, organ meats, and breast milk.
Linoleic acid is an 18-carbon long polyunsaturated fatty acid containing two double bonds. Its first double bond occurs at the sixth carbon from the omega end, classifying it as an omega-6 oil. As linoleic acid is absorbed and metabolized in the human body, it is converted into a derivative fatty acid, gamma linoleic acid (GLA), which is converted into di-homo-gamma linoleic acid (DGLA) and arachidonic acid (AA). The DGLA and AA are then converted into two types of prostaglandins by adding two carbon molecules and removing hydrogen molecules. There are three families of prostaglandins, PGE1, PGE2, and PGE3. DGLA is converted to PGE1, while AA is converted into PGE2. PGE3 is made by the conversion of omega-3 fatty acids. Both PGE1 and PGE3, anti-inflammatory agents, protect against coronary disease by keeping blood platelets slippery and flowing, thus preventing blood clotting. PGE2 is inflammatory and increases platelet stickiness and blood clotting. All three forms must be present to ensure a functioning clotting system. There must be enough PGE2 to ensure healthy clotting, but enough PGE1 and PGE3 to protect against too much clotting, which can lead to hardening of the arteries, heart attack, and stroke. Likewise, PGE1 appears to act as a diuretic, while PGE2 aids in the retention of water and salts in the kidneys. PGE2 also is required for healthy brain and synapse functioning. The three types of prostaglandins serve as a system of checks and balances within the body.
However, if AA and its derivative, PGE2, are over-produced or imbalanced with PGE1 and PGE3, they can
Daily consumption of omega-6 fatty acids by many people may be excessive, due to the presence of omega-6 fatty acids in common cooking vegetable oils and processed foods. The ratio of omega-6 to omega-3 fatty acid consumption can often reach 20:1. To achieve a more desirable ratio, an approach is to eliminate sources of omega-6 fatty acids, especially those hidden in processed foods and to increase the amount of omega-3 fatty acids consumed through fish oil or flaxseed supplements. In addition, to convert the omega-6 fatty acids present in oils (such as corn, safflower, or soybean) to GLA requires that the oils be unprocessed and unheated and in the natural form (cis form). In oils that have undergone processing (heating and/or hydrogenation) to prolong shelf life (e.g., many store bought oils) or to form a solid at room temperature (e.g., shortening and margarine), the fatty acid structure has been changed to the trans form, and the conversion process of omega-6 fatty acids to GLA may be inhibited.
Author Info: Judith Sims, Rebecca J. Frey PhD, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Alternative Medicine, 2005
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