Current reviews and textbooks call the omega-6 linoleic acid and the omega-3 alpha-linolenic acid “essential fatty acids” (EFA) and cite the EFA requirement as one to four percent of calories. Research suggests, however, that the omega-6 arachidonic acid (AA) and the omega-3 docosahexaenoic acid (DHA) are the only fatty acids that are truly essential. Eicosapentaenoic acid (EPA) occurs in fish products but is probably not a normal constituent of the mammalian body and in excess it interferes with essential AA metabolism. The EFA requirement cited in the scientific literature is inflated by several factors: the use of diets composed mostly of sucrose, glucose, or corn syrup; the use of diets deficient in vitamin B6; the use of purified fatty acids instead of whole foods; the use of questionable biochemical markers rather than verifiable symptoms as an index for EFA deficiency; and the generalization from studies using young, growing animals to adults. The true requirement for EFA during growth and development is less than 0.5 percent of calories when supplied by most animal fats and less than 0.12 percent of calories when supplied by liver. On diets low in heated vegetable oils and sugar and rich in essential minerals, biotin, and vitamin B6, the requirement is likely to be much lower than this. Adults recovering from injury, suffering from degenerative diseases involving oxidative stress, or seeking to build muscle mass mass may have a similar requirement. For women who are seeking to conceive, pregnant, or lactating, the EFA requirement may be as high as one percent of calories. In other healthy adults, however, the requirement is infinitesimal if it exists at all. The best sources of EFAs are liver, butter, and egg yolks, especially from animals raised on pasture. During pregnancy, lactation, and childhood, small amounts of cod liver oil may be useful to provide extra DHA, but otherwise this supplement should be used only when needed to obtain fat-soluble vitamins. Vegetarians or others who eat a diet low in animal fat should consider symptoms such as scaly skin, hair loss or infertility to be signs of EFA deficiency and add B6 or animal fats to their diets. An excess of linoleate from vegetable oil will interfere with the production of DHA while an excess of EPA from fish oil will interfere with the production and utilization of AA. EFA are polyunsaturated fatty acids (PUFA) that contribute to oxidative stress. Vitamin E and other antioxidant nutrients cannot fully protect against oxidative stress induced by dietary PUFA. Therefore, the consumption of EFA should be kept as close to the minimum requirement as is practical while still maintaining an appetizing and nutritious diet.
Bottom line: NOT VERY ESSENTIAL. Don’t flood your body with PUFA. You get plenty from butter, eggs, fish, and other animal products. Any more than that leads to inflammation and atherosclerosis.
Don’t use veggie oil, don’t supplement with omega 6 or omega 3.