Conjugated linoleic acid impairs endothelial function.

OBJECTIVE To determine the effect of dietary supplementation with conjugated linoleic acid (CLA) on body mass index (BMI), body fat distribution, endothelial function, and markers of cardiovascular risk. METHODS AND RESULTS Forty healthy volunteers with BMI >27 kg/m2 were randomized to receive a CLA isomeric mixture or olive oil in a 12-week double-blind study. Subcutaneous body fat and abdominal/hepatic fat content were assessed using skin-fold thicknesses and computed tomography scanning, respectively. Endothelial function was assessed by brachial artery flow-mediated dilatation (FMD). Plasma isoprostanes were measured as an index of oxidative stress. CLA supplementation did not result in a significant change in BMI index or total body fat. There was a significant decrease in limb (-7.8 mm, P<0.001), but not torso skin-fold thicknesses or abdominal or liver fat content. Brachial artery FMD declined (-1.3%, P=0.013), and plasma F2-isoprostanes increased (+91 pg/mL, P=0.042). CONCLUSIONS A CLA isomeric mixture had at most modest effects on adiposity and worsened endothelial function. On the basis of these results, the use of the isomeric mixture of CLA as an aid to weight loss cannot be recommended.