Omega−3 fatty acids, also called ω−3 fatty acids orn−3 fatty acids, are polyunsaturated fatty acidscharacterized by the presence of a double bond threeatoms away from the terminal methyl group in theirchemical structure. They are widely distributed innature, being important constituents of animal lipidmetabolism, and they play an important role in thehuman diet and in human physiology. The three types of omega−3 fattyacids involved in human physiology are α-linolenic acid, found in plantoils, and eicosapentaenoic acid and docosahexaenoic acid, bothcommonly found in marine oils. Marine algae and phytoplankton areprimary sources of omega−3 fatty acids. Common sources of plant oilscontaining ALA include walnut, edible seeds, clary sage seed oil, algal oil, flaxseed oil, Sacha Inchi oil, Echium oil, and hemp oil, while sources ofanimal omega−3 fatty acids EPA and DHA include fish, fish oils, eggsfrom chickens fed EPA and DHA, squid oils, and krill oil.
Sterols of plants are called phytosterols and sterols of animals are called zoosterols. The most important zoosterol is cholesterol; notable phytosterols include campesterol, sitosterol, and stigmasterol. Ergosterol is a sterol present in the cell membrane of fungi, where it serves a role similar to cholesterol in animal cells.