Trans-Fatty Acids

Abstract

By pumping hydrogen into edible oils (with heat and nickel catalyst) their fatty acids become more saturated and the oil solidifies. Hydrogenation was used from around 1912 to make the original margarines, which became the poor persons’ butter. If hydrogenation is not taken to completion and some double bonds remain, some of them now have their hydrogen atoms on opposite sides i.e., in trans form (changed from natural cis form, with both hydrogens on the same side of a double bond). The molecule changes shape and the oil’s melting point goes up. The major industrial trans fatty acid is 18:1 trans, called elaidic.

Early human experiments with trans fatty acids (TFAs) had inconsistent effects on serum cholesterol, but from 1990, with more precise composition of test fats comparing 18:1 trans (elaidic) with 18:1 (oleic), TFAs raised serum LDL-c and at very high intakes (8–11% energy %) also lowered HDL-c. As to epidemiology, cohort studies with food frequency questionnaires suggest TFAs increase risk of CHD; case-control studies based on adipose tissue TFA did not.

Trans fatty acids are also made by microbial biohydrogenation in the rumen of cows and sheep so a small percentage of the fatty acids in beef, lamb and dairy foods is natural trans 18:1, vaccenic acid. Its double bonds are in different position from elaidic. There were no human experiments in the twentieth century to test the biological effects of vaccenic acid, i.e., non-industrial TFA. Years (1975), 1990–1995.