Polyunsaturated fatty acids (PUFA) are incorporated into membranes where they alter membrane fluidity and are also the precursors to a group of signal molecules called the eicosanoids. Two PUFAs that are required by the body for eicosanoid formation are α-linolenic acid and linoleic acid. Because these fatty acids cannot be synthesised in the body, and must be present for normal metabolic function to continue, they are classed as essential dietary components. Both α-linolenic acid and linoleic acid are named after Linum usitatissimum (the flax plant) from which they were first isolated by German scientists in 1886 and 1887, respectively. The essential fatty acids α-linolenic acid and linoleic acid belong to the omega 3 (n-3) and omega 6 (n-6) groups of unsaturated fatty acids, respectively. The omega designation is the last carbon in the fatty acid chain, the number the placement of the first double bond from the omega carbon.
Their essential nature of the fatty acids is highlighted by their original designation as vitamin F, after their discovery in 1929 by the researcher Burr and Burr1. The researchers deprived rats of PUFAs and reported a specific disease condition that could be reversed upon administration of the fat back to the diet of the rats. The disease was described as the presence of a scaly texture to the skin, an inflamed and swollen tip of the tail that develops into a heavily scaled and ridged tail and then subsequent necrosis and loss of the tip. The hair becomes filled with dandruff and the hind legs become swollen. Sores appear, and hair loss occurs around the face, back and neck. Growth eventually ceases and the animal loses weight and dies within 3 or 4 months. In a subsequent paper2, the same authors discovered that vitamin F was actually two separate fatty acids.