Lipid made up of a hydrocarbon chain of variable length with a carboxyl group (-COOH) at one end, and a methyl group at the other. Saturated fatty acids and mono or polyunsaturated fatty acids (PUFA) are classified according to the presence or absence of double bonds between carbon atoms within the molecule. The essential fatty acids known as “Omega 3s” are polyunsaturated with 3 to 6 double bonds, the first of these being in the 3rd position from the end of the molecule.