Essential fatty acids

Fatty acids form part of a number of essential compounds in the animal body (e.g. membrane phospholipids). Most of the fatty acids can be synthesized by the animals de novo from acetate as a precursor. Fatty acids produced in this way are saturated, but they usually undergo a partial desaturation to form monoenoic acids (of one unsaturated bond) of varying chain length. The requirement for essential fatty acids (EFA) which cannot be synthesized de novo by the animal was demonstrated for rats by Burr & Burr (1929) and later for many other animals, and is probably general to all higher vertebrates. Signs of deficiency were avoided by supplementing the oil deficient diet with linoleic acid (18:2ω6), an unsaturated lipid found in many vegetable oils such as those of corn, peanut and sunflower seeds. Supplementation with linolenic acid (18:3ω3) partially corrected the condition, but was not as efficient as linoleic acid. The dietary acids of the ω6 group have been found to be precursors of prostaglandins and also provide a substrate for the pre-oxidation of microsomal fats in the liver. Fatty acids of the ω3 group (e.g. linolenic acid) are non-essential for higher vertebrates, although they can replace to some extent the essential ω6 acids.

Animals can further desaturate and elongate the chains of the dietary unsaturated fatty acids to form polyunsaturated fatty acids (PUFA). Different animals and even different species have a different capacity to elongate fatty acids.