Structures of cis- and trans fatty acids.

Elaidic acid (9-trans-C18:1) is a typical industrial trans fatty acid, produced by partial hydrogenation of vegetable oil. Vaccenic acid (11-trans-C18:1) is the predominant trans fatty acid in milk and meat from ruminant animals, although small amounts are also found in industrially hydrogenated fats. The 9,11 isomer of conjugated linoleic acid or CLA (9-cis, 11-trans-C18:2) is found almost exclusively in ruminant fat; industrial production of CLA yields a mixture of 9,11 and 10,12 isomers. Oleic acid (9-cis -C18:1) is the predominant cis-unsaturated fatty acid in the diet. The location of the trans bond in trans isomers of alpha-linolenic acid is not known precisely; for this figure it has been assigned arbitrarily to the 6 location. The same holds for the trans bonds in the trans isomers of C20:1, C20:2, C22:1 and C22:2 that arise from eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) during partial hydrogenation of fish oil.