Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome.
OBJECTIVE
Conjugated linoleic acid (CLA) is a group of dietary fatty acids with antiobesity and antidiabetic effects in some animals. The trans10cis12 (t10c12) CLA isomer seems to cause these effects, including improved insulin sensitivity. Whether such isomer-specific effects occur in humans is unknown. The aim of this study was to investigate whether t10c12 CLA or a commercial CLA mixture could improve insulin sensitivity, lipid metabolism, or body composition in obese men with signs of the metabolic syndrome.


METHODS
In a randomized, double-blind controlled trial, abdominally obese men (n = 60) were treated with 3.4 g/day CLA (isomer mixture), purified t10c12 CLA, or placebo. Euglycemic-hyperinsulinemic clamp, serum hormones, lipids, and anthropometry were assessed before and after 12 weeks of treatment.


RESULTS
Baseline metabolic status was similar between groups. Unexpectedly, t10c12 CLA increased insulin resistance (19%; P < 0.01) and glycemia (4%; P < 0.001) and reduced HDL cholesterol (-4%; P < 0.01) compared with placebo, whereas body fat, sagittal abdominal diameter, and weight decreased versus baseline, but the difference was not significantly different from placebo. The CLA mixture did not change glucose metabolism, body composition, or weight compared with placebo but lowered HDL cholesterol (-2%; P < 0.05).


CONCLUSIONS
These results reveal important isomer-specific metabolic actions of CLA in abdominally obese humans. A CLA-induced insulin resistance has previously been described only in lipodystrophic mice. Considering the use of CLA-supplements among obese individuals, it is important to clarify the clinical consequences of these results, but they also provide physiological insights into the role of specific dietary fatty acids as modulators of insulin resistance in humans.
Risérus
Ulf
U
Department of Public Health and Caring Sciences/Geriatrics, Uppsala University, Uppsala, Sweden. ulf.riserus@pubcare.uu.se
Arner
Peter
P
Brismar
Kerstin
K
Vessby
Bengt
B
D000328:Adult; D000368:Aged; D001823:Body Composition; D003920:Diabetes Mellitus / Q000188:drug therapy*; D004311:Double-Blind Method; D006801:Humans; D006949:Hyperlipidemias / Q000139:chemically induced*; D007333:Insulin Resistance; D007536:Isomerism; D020738:Leptin / Q000097:blood; D019787:Linoleic Acid / Q000009:adverse effects* / Q000737:chemistry; D008074:Lipoproteins / Q000097:blood; D008297:Male; D024821:Metabolic Syndrome / Q000188:drug therapy*; D008875:Middle Aged; D009765:Obesity
D020738:Leptin; D008074:Lipoproteins; D019787:Linoleic Acid