Trans fatty acids and blood lipids

Intake of trans-unsaturated fatty acids (TFA) has been consistently shown in multiple and rigorous randomized trials to have adverse effects on blood lipids, most notably on the LDL:HDL cholesterol ratio, which is a strong marker of cardiovascular risk. When a mixture of TFA isomers obtained by partial hydrogenation of vegetable oils is used to replace oleic acid, there is a dose-dependent increase in the LDL:HDL ratio. The relationship between amount of TFA as % of energy and the increase in the LDL:HDL ratio appears to be approximately linear, with no evidence of a threshold at low levels of intake, and with slope twice as steep as that observed by replacing oleic with saturated fats. The average impact of TFA induced changes in the LDL:HDL ratio correspond to tens of thousands premature deaths in the US alone. Although dramatic, this effect is substantially smaller than the increase in cardiovascular mortality associated with TFA intake in epidemiological studies, suggesting that other mechanisms are likely to contribute to the toxicity of TFA.