The 'essential'<unk>  acids were given their name when researchers found that they are essential to normal growth in young children and animals. The<unk>  DHA, also known as docosahexaenoic acid, is found in high abundance in the human brain. It is produced by a desaturation process, but humans lack the desaturase enzyme, which acts to insert double bonds at the ω6 and ω3 position. Therefore, the ω6 and ω3 polyunsaturated<unk>  acids cannot be synthesized, are appropriately called essential<unk>  acids, and must be obtained from the diet. In 1964, it was discovered that enzymes found in sheep tissues convert omega−6 arachidonic acid into the inflammatory agent, prostaglandin E2, which is involved in the immune response of traumatized and infected tissues. By 1979, eicosanoids were further identified, including thromboxanes, prostacyclins, and leukotrienes. The eicosanoids typically have a short period of activity in the body, starting with synthesis from<unk>  acids and ending with metabolism by enzymes. If the rate of synthesis exceeds the rate of metabolism, the excess eicosanoids may have deleterious effects. Researchers found that certain<unk> s are also converted into eicosanoids and docosanoids, but at a slower rate. If both omega−3 and omega−6<unk>  acids are present, they will "compete" to be transformed, so the ratio of long-chain omega−3:omega−6<unk>  acids directly affects the type of eicosanoids that are produced. Interconversion Conversion efficiency of ALA to EPA and DHA Humans can convert short-chain<unk> s to long-chain forms (EPA, DHA) with an efficiency below 5%. The omega−3 conversion efficiency is greater in women than in men, but less studied. Higher ALA and DHA values found in plasma phospholipids of women may be due to the higher activity of desaturases, especially that of delta-6-desaturase. These conversions occur competitively with omega−6<unk>  acids, which are essential closely related chemical analogues that are derived from linoleic acid. They both utilize the same desaturase and elongase proteins in order to synthesize inflammatory regulatory proteins. The products of both pathways are vital for growth making a balanced diet of omega−3 and omega−6 important to an individual's health. A balanced intake ratio of 1:1 was believed to be ideal in order for proteins to be able to synthesize both pathways sufficiently, but this has been controversial as of recent research. The conversion of ALA to EPA and further to DHA in humans has been reported to be limited, but varies with individuals. Women have higher ALA-to-DHA conversion efficiency than men, which is presumed to be due to the lower rate of use of dietary ALA for beta-oxidation. One preliminary study showed that EPA can be increased by lowering the amount of dietary linoleic acid, and DHA can be increased by elevating intake of dietary ALA. Omega−6 to omega−3 ratio Human diet has changed rapidly in recent centuries resulting in a reported increased diet of omega−6 in comparison to omega−3. The rapid evolution of human diet away from a 1:1 omega−3 and omega−6 ratio, such as during the Neolithic Agricultural Revolution, has presumably been too fast for humans to have adapted to biological profiles adept at balancing omega−3 and omega−6 ratios of 1:1. This is commonly believed to be the reason why modern diets are correlated with many inflammatory disorders. While omega−3 polyunsaturated<unk>  acids may be beneficial in preventing heart disease in humans, the level of omega−6 polyunsaturated<unk>  acids (and, therefore, the ratio) does not matter. Both omega−6 and<unk> s are essential: humans must consume them in their diet. Omega−6 and omega−3 eighteen-carbon polyunsaturated<unk>  acids compete for the same metabolic enzymes, thus the omega−6:omega−3 ratio of ingested<unk>  acids has significant influence on the ratio and rate of production of eicosanoids, a group of hormones intimately involved in the body's inflammatory and homeostatic processes, which include the prostaglandins, leukotrienes, and thromboxanes, among others. Altering this ratio can change the body's metabolic and inflammatory state. In general, grass-fed animals accumulate more omega−3 than do grain-fed animals, which accumulate relatively more omega−6. Metabolites of omega−6 are more inflammatory (esp. arachidonic acid) than those of omega−3. This necessitates that omega−6 and omega−3 be consumed in a balanced proportion; healthy ratios of omega−6:omega−3, according to some authors, range from 1:1 to 1:4. Other authors believe that a ratio of 4:1 (4 times as much omega−6 as omega−3) is already healthy. Studies suggest the evolutionary human diet, rich in game animals, seafood, and other sources of omega−3, may have provided such a ratio. Typical Western diets provide ratios of between 10:1 and<unk> 0:1 (i.e., dramatically higher levels of omega−6 than omega−3). The ratios of omega−6 to<unk> s in some common vegetable oils are: canola 2:1, hemp 2–3:1, soybean 7:1, olive<unk> –13:1, sunflower (no omega−3), flax 1:3, cottonseed (almost no omega−3), peanut (no omega−3), grapeseed oil (almost no omega−3) and corn oil 46:1.
Omega-3 fatty acid
Omega-6 fatty acid
Cholic acid
Omega-3 acid ethyl esters
Fish oil
Fish oil 
Phytosterol
Saturated fat