Fatty acids are straight chain hydrocarbons possessing a carboxyl (COOH) group at one end (α) and (usually) a methyl group at the other (ω) end. In physiology, EFAs are named by the position of the first double bond from the ω end. For example, the term ω-3 signifies that the first double bond exists as the third carbon-carbon bond from the terminal CH₃ end (ω) of the carbon chain. The number of carbons and the number of double bonds is also listed. ω-3 18:4 (stearidonic acid) indicates an 18-carbon chain with 4 double bonds, and with the first double bond in the third position from the CH₃ end. Double bonds are cis and separated by a single methylene (CH₂) group unless otherwise noted. So in free fatty acid form, the chemical structure of stearidonic acid is:

What is "Essential"?

Between 1930 and 1950, arachidonic acid and linolenic acid were termed 'essential' because each was more or less able to meet the growth requirements of rats given fat-free diets. Further research has shown that human metabolism requires both ω-3 and ω-6 fatty acids. To some extent, any ω-3 and any ω-6 can relieve the worst symptoms of fatty acid deficiency. Particular fatty acids are still needed at critical life stages (e.g. lactation) and in some disease states. See (Cunnane 2003)^[3] for a discussion of the current status of the term 'essential'.

Examples