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Effects of cis-9,trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men^1,2,3

¹ From the Clinical Nutrition Research Unit, Department of Public Health and Caring Sciences/Geriatrics, Uppsala University, Uppsala, Sweden

Background: We recently showed that trans-10,cis-12 (t10,c12) conjugated linoleic acid (CLA) causes insulin resistance in obese men. However, metabolic effects of the c9,t11 CLA isomer are still unknown in obese men. Because c9,t11 CLA is the predominant CLA isomer in foods and is included in dietary weight-loss products, it is important to conduct randomized controlled studies that use c9,t11 CLA preparations.

Objective: We investigated the effects of c9,t11 CLA supplementation on insulin sensitivity, body composition, and lipid peroxidation in a group at high risk for cardiovascular disease.

Design: In a randomized, double-blind, placebo-controlled study, 25 abdominally obese men received 3 g c9,t11 CLA/d or placebo (olive oil). Before and after 3 mo of supplementation, we assessed insulin sensitivity (hyperinsulinemic euglycemic clamp), lipid metabolism, body composition, and urinary 8-iso-prostaglandin F₂ (a major F₂-isoprostane) and 15-keto-dihydro-prostaglandin F₂, markers of in vivo oxidative stress and inflammation, respectively.

Results: All subjects completed the study. Compared with placebo, c9,t11 CLA decreased insulin sensitivity by 15% (P < 0.05) and increased 8-iso-prostaglandin F₂ and 15-keto-dihydro-prostaglandin F₂ excretion by 50% (P < 0.01) and 15% (P < 0.05), respectively. The decreased insulin sensitivity was independent of changes in serum lipids, glycemia, body mass index, and body fat but was abolished after adjustment for changes in 8-iso-prostaglandin F₂ concentrations. There were no differences between groups in body composition.

Conclusions: A CLA preparation containing the purified c9,t11 CLA isomer increased insulin resistance and lipid peroxidation compared with placebo in obese men. Because c9,t11 CLA occurs in commercial supplements as well as in the diet, the present results should be confirmed in larger studies that also include women.

Key Words: trans Fatty acids • fatty acids • conjugated linoleic acid • dairy fat • diet • insulin resistance • abdominal obesity • inflammation • oxidative stress • lipid peroxidation

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