Polyunsaturated fatty acids contain more than one double bond along the chain. The term "unsaturated" indicates that fewer than the maximum possible
number of hydrogen atoms are bonded to each carbon in the molecule. The number of double bonds is indicated by the generic name - monounsaturated for
molecules with one double bond or polyunsaturated for molecules with more than one double bond.
Polyunsaturated fats with two double bonds usually have one between carbons 9 and 10 in the alkyl chain and another three carbons away (carbons 12-13).
The presence of a double bond in the fatty acid chain changes the shape of the side group, and alters membrane fluidity when present in phospholipids.
Polyunsaturated fatty acids in the diet such as Ω-3 fatty acids from
may have a positive influence on health,
reducing cardiovascular disease and cancer.
The double bonds, as few as two or as many as six, are located in a series beginning at either the third or the sixth carbon atom from the methyl end
of the molecule and extending toward the carboxyl group. The biological properties of polyunsaturated fatty acids are related to these three
characteristics, although not necessarily in a uniform way.
Linoleic acid, the principal Ω-6 polyunsaturated fatty acid in the diet, and the Ω-3 polyunsaturated fatty acids are beneficial
in reducing inflammation, and lowering LDL cholesterol.