Required fat nutrients for good health. Humans and animals must get these nutrients from food because they cannot be synthesized in the body. The two EFAs, linolenic and linoleic acid, are used to build specialized fats Omega-3 and Omega-6 fatty acids, critical for the normal functioning of all tissues of the body. Omega-3s are used in the formation of cell walls and assist in improving circulation and oxygen uptake. Fish oils and flaxseed are the most popular sources for EFAs.