Omega-3 fatty acids (also called ω-3 fatty acids or n-3 fatty acids) are polyunsaturated fatty acids (PUFAs) with a double bond (C=C) at the third carbon atom from the end of the carbon chain. The fatty acids have two ends, the carboxylic acid (-COOH) end, which is considered the beginning of the chain, thus “alpha”, and the methyl (CH3) end, which is considered the “tail” of the chain, thus “omega.” The way in which a fatty acid is named is determined by the location of the first double bond, counted from the methyl end, that is, the omega (ω-) or the n- end. The three types of omega-3 fatty acids involved in human physiology are α-linolenic acid (ALA) (found in plant oils), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) (both commonly found in marine oils). Marine algae and phytoplankton are primary sources of omega-3 fatty acids. Common sources of plant oils containing the omega 3 ALA fatty acid include walnut, edible seeds, clary sage seed oil, algal oil, flaxseed oil, Sacha Inchi oil, Echium oil, and hemp oil, while sources of animal omega-3 EPA and DHA fatty acids include fish oils, egg oil, squid oils, and krill oil. Supplementation with omega-3 fatty acids does not appear to affect the risk of death, cancer or heart disease. Omega-3 fatty acids are important for normal metabolism. Mammals have a limited ability to synthesize omega-3 fats when the diet includes the shorter-chain omega-3 fatty acid ALA, 18 carbons and 3 double bonds) to form the more important long-chain omega-3 fatty acids, EPA, 20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA, 22 carbons and 6 double bonds) with even greater inefficiency. The ability to make the longer-chain omega-3 fatty acids from ALA may also be impaired in aging. In foods exposed to air, unsaturated fatty acids are vulnerable to oxidation and rancidity.