Metabolic Effects of CLA in Humans: The Swedish Experience.
Conjugated linoleic acid (CLA) comprises a group of unsaturated fatty acid isomers with a variety of biological effects. CLA reduces body fat accumulation in animal models and has been ascribed significant effects on lipid and glucose metabolism. It has been suggested that the trans10-cis12 isomer is the active isomer as regards antiobesity and insulin sensitizing properties. The metabolic effects in humans are not well characterized. We have investigated the effects of CLA (given as the commercially available mixture of isomers and as the purified trans10-cis12 CLA isomer) on anthropometry, lipid and glucose metabolism and on markers of lipid peroxidation. Preliminary results indicate that CLA may slightly decrease body fat also in humans, particularly abdominal fat, but there is no effect on body weight or body mass index. There is no simultaneous improvement of lipid or glucose metabolism. Rather, the trans 10-cis12 CLA isomer unexpectedly caused significant impairment of the peripheral insulin sensitivity as well as of blood glucose and serum lipid levels. In addition, CLA markedly elevated lipid peroxidation. Thus, the metabolic effects of CLA in humans seem complex and further studies, especially of isomer specific effects and during longer time periods, are needed.