Effects of cis-9,trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men.

Randomized, double-blind, placebo-controlled trial in abdominally obese white men at high cardiovascular risk. Men were 35 to 65 years old, with BMI 27 to 35 kg/m2; 13 participants were randomized to the c9,t11 CLA arm.

The active intervention was oral cis-9,trans-11 conjugated linoleic acid (CLA), 3 g/day given as 6 capsules/day for 3 months. The preparation was 83% c9,t11 CLA and provided about 2.5 g/day c9,t11 CLA plus about 0.2 g/day t10,c12 CLA; the placebo was olive oil.

Overall, purified c9,t11 CLA had an unfavorable effect on metabolic health in these obese men. Compared with placebo, insulin sensitivity decreased by 15% (P = 0.05), and mean insulin-mediated glucose uptake was also lower with c9,t11 CLA (P = 0.05). Markers of lipid peroxidation increased, including 8-iso-prostaglandin F2alpha by 50% (P = 0.01) and 15-keto-dihydro-prostaglandin F2alpha by 15% (P = 0.05). Lipoproteins, triacylglycerol, and free fatty acids did not differ significantly, but body weight and BMI increased within the c9,t11 CLA group over 12 weeks. No side effects or liver enzyme abnormalities were reported.

Small trial with only 13 participants in the active arm and 3-month follow-up. Findings are limited to abdominally obese white men, so generalizability to women and other populations is uncertain. Complete clamp data were unavailable for 2 randomized participants, and the study did not assess longer-term clinical outcomes.