Omega-3 fatty acids are polyunsaturated fatty acids (PUFA) important for normal metabolism. The three types of omega-3 fatty acids involved in human physiology are α-Linolenic acid, or ALA (found in plant oils), eicosapentaenoic acid or EPA, and docosahexaenoic acid or DHA (both commonly found in marine oils). Common sources of plant oils containing ALA fatty acids include walnuts, clary sage seed oil, algal oil, flaxseed oil, and hemp oil, while sources of animal omega-3 EPA and DHA fatty acids include fish oil, egg oil, squid oil, and krill oil.
Mammals have a limited ability to synthesize omega-3 fats when the diet includes the shorter-chain omega-3 fatty acid, ALA to form the more important long-chain omega-3 fatty acids EPA, and then from EPA to the most crucial, DHA with even greater inefficiency. The ability to make the longer-chain omega-3 fatty acids from ALA may also be impaired and decreased in aging. When foods are exposed to air, unsaturated fatty acids are susceptible to oxidation and rancidity.