Conjugated linoleic acids reduce body fat in healthy postmenopausal women.

Isomers of conjugated linoleic acids (CLA) reduce fat mass (FM) and increase insulin sensitivity in some, but not all, murine studies. In humans, this effect is still debatable. In this study, we compared the effect of 2 CLA supplements on total and regional FM assessed by dual energy X-ray absorptiometry, changes in serum insulin and glucose concentrations, and adipose tissue (AT) gene expression in humans. In a double-blind, parallel, 16-wk intervention, we randomized 81 healthy postmenopausal women to 1) 5.5 g/d of 40/40% of cis9,trans11-CLA (c9,t11-CLA) and trans10,cis12-CLA (t10,c12-CLA) (CLA-mix); 2) cis9, trans11-CLA (c9,t11-CLA); or 3) control (olive oil). We assessed all variables before and after the intervention. The CLA-mix group had less total FM (4%) and lower-body FM (7%) than the control (P = 0.02 and < 0.001, respectively). Post hoc analyses showed that serum insulin concentrations were greater in the CLA-mix group (34%) than the control group (P = 0.02) in the highest waist circumference tertile only. AT mRNA expression of glucose transporter 4, leptin, and lipoprotein lipase was lower, whereas expression of tumor necrosis factor-alpha was higher in the CLA-mix group than in the control group (P < 0.04). In conclusion, a 50:50 mixture of c9,t11- and t10,c12-CLA isomers resulted in less total and lower-body FM in postmenopausal women and greater serum insulin concentrations in the highest waist circumference tertile. Future research is needed to confirm the insulin desensitizing effect of the CLA mixture and the effect on the mRNA expression of adipocyte-specific genes in humans.

An oil mixture with trans-10, cis-12 conjugated linoleic acid increases markers of inflammation and in vivo lipid peroxidation compared with cis-9, trans-11 conjugated linoleic acid in postmenopausal women.

A mixture of trans-10, cis-12 (t10,c12) and cis-9, trans-11 (c9,t11) conjugated linoleic acid (CLA mixture) reduced atherosclerosis in animals, thus the effect of these isomers on endothelial dysfunctions leading to inflammation and atherosclerosis is of interest. We gave 75 healthy postmenopausal women a daily supplement of 5.5 g of oil rich in either CLA mixture, an oil rich in the naturally occurring c9,t11 CLA (CLA milk), respectively, or olive oil for 16 wk in a double-blind, randomized, parallel intervention study. We sampled blood and urine before and after the intervention. The ratios of total cholesterol:HDL cholesterol and concentrations of C-reactive protein, fibrinogen, and plasminogen activator inhibitor-1 were significantly higher in women supplemented with the CLA mixture than in those supplemented with CLA milk. Plasma triacylglycerol was significantly higher and HDL cholesterol was lower in women supplemented with the CLA mixture than with olive oil. Both CLA supplements increased lipid peroxidation, a marker of in vivo oxidative stress measured as urinary free 8-iso-prostaglandin F(2alpha). However, the CLA mixture increased lipid peroxidation more than the CLA milk did. The plasma cytokines interleukin-6 and tumor necrosis factor-alpha were not affected by the treatments, nor were any of the other variables measured. In conclusion, oil containing trans-10,cis-12 CLA has several adverse effects on classical and novel markers of coronary vascular disease, whereas the c9,t11 CLA isomer is more neutral, except for a small but significant increase in lipid peroxidation compared with olive oil.