Trans fatty acids and insulin resistance.

Since trans fatty acids (TFA) might interfere with cell membrane functions, there are reasons to believe that high TFA intakes could affect insulin sensitivity and consequently diabetes risk. It is possible that low amounts of TFA consumed during long time-periods might be clinically relevant. Data from controlled intervention studies investigating the effects of TFA on insulin sensitivity are reviewed. The results show no significant effect of TFA on insulin sensitivity in lean healthy subjects. However, there is some evidence that TFA could impair insulin sensitivity compared to unsaturated fat in insulin resistant or diabetic individuals. This is especially true for conjugated TFA, i.e. conjugated linoleic acid (CLA), which clearly impairs insulin sensitivity. In fact, the effect of CLA on insulin action is the most dramatic adverse effect described for a dietary fatty acid. The inconsistent effect of TFA as a group might partly be due to methodological limitations (e.g. few studies, short duration or small sample size) and differences between studies in design, type and amount of TFA used. Large controlled trials have been required to demonstrate adverse effects of saturated fat on insulin sensitivity, and similar efforts will probably be needed to clarify the effect of TFA on insulin sensitivity.