Trans-fatty acids (TFA) are unsaturated fatty acids that have double bonds in the trans- configuration. The trans-double bonds in unsaturated fatty acids causes the molecules to have a different structure to their cis-double bond counterparts. A trans-configuration double bond tend to create a straighter carbon chain, whereas a cis-double bond creates a carbon chain with a pronounced kink. As a result of these structural differences, TFA have physiological effects in the body that are different to cis-fatty acids. Naturally occurring TFA include trans-vaccenic acid, a TFA present in the human diet in small amounts from the milk and meat of ruminants. Trans-fatty acids can also be found in hydrogenated vegetable oils and deodorised oils. However, these TFA are more numerous, and artificially produced from their natural cis-fatty acid counterparts as a by-product of the industrial manufacturing process.
In investigate the effects of TFA on health, researchers1 fed 46 healthy subjects 11 to 12 grams per day of TFA from either natural or industrial sources. The TFA represented about 5 % of calories. The results showed that plasma levels of HDL were significantly lower in women who consumed TFA from the industrial source, with a significant difference found for all subjects. In addition, the plasma concentration of LDL cholesterol was significantly higher in those women consuming natural TFA as compared to industrial TFA. Total cholesterol and plasma triacylglycerols were also higher in those eating the natural source TFA. There was no significant difference in VLDL levels and no differences detected in men between treatments. These results suggest that TFA from natural ruminant sources and industrial sources have different physiological effects in women.
The changes to both HDL and LDL make it difficult to draw any conclusions from this data regarding cardiovascular risk. The most prevalent TFA in both natural and industrial sources were the trans-9, trans-10 and trans-11 18:1 variants. Of these, trans-11 18:1 was the most common TFA from natural sources and trans-9 18:1 was the most common TFA from industrial sources. Trans-vaccenic acid from ruminant fat is a substrate for stearoyl-CoA desaturase, which is an enzyme that can convert trans-vaccenic acid (trans-11 18:1) into rumenic acid (cis-9, trans-11 18:2), a conjugated isomer of linoleic acid (LA, 18:2 (n-6)). This conversion has been estimated to be around 20 % in humans, and the resultant conjugated linoleic acid (CLA has been shown to be beneficial to health in a number of ways, including having anti-obesity effects.
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