<unk> s, also called Omega-3 oils,<unk> tty acids or n−3<unk>  acids, are polyunsaturated<unk>  acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chemical structure. They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. The three types of<unk> s involved in human physiology are α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA can be found in plants, while DHA and EPA are found in algae and fish. Marine algae and phytoplankton are primary sources of<unk> s. DHA and EPA accumulate in fish that eat these algae. Common sources of plant oils containing ALA include walnuts, edible seeds, and flaxseeds, while sources of EPA and DHA include fish and fish oils. Mammals are unable to synthesize the essential<unk>  ALA and can only obtain it through diet. However, they can use ALA, when available, to form EPA and DHA, by creating additional double bonds along its carbon chain (desaturation) and extending it (elongation). Namely, ALA (18 carbons and<unk>  double bonds) is used to make EPA (20 carbons and 5 double bonds), which is then used to make DHA (22 carbons and 6 double bonds). The ability to make the longer-chain<unk> s from ALA may be impaired in aging. In foods exposed to air, unsaturated<unk>  acids are vulnerable to oxidation and rancidity. There is no high-quality evidence that dietary supplementation with<unk> s reduces the risk of cancer or cardiovascular disease. Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes or any vascular disease outcomes.
Omega-3 fatty acid
Omega-6 fatty acid
Cholic acid
Omega-3 acid ethyl esters
Fish oil
Fish oil 
Phytosterol
Saturated fat