Conjugates linoleic acid (CLA) is a name given to a group of fatty acids that are isomers of linoleic acid with conjugated double bonds. The cis-9 trans-11 isomer of conjugated linoleic acid is found naturally in ruminants and is the most abundant of the isomers of CLA in the human diet. Supplemental CLA has shown promise as a weight loss aid and mixtures of the trans-10 cis-12 and cis-9 trans-11 isomers of CLA are marketed in weight loss capsules in a 50/50 ratio. Rodent studies with the trans-10 cis-12 isomer have shown that CLA is effective at inducing weight loss in mice, with various adipose regions being more sensitive to fat loss from CLA than others. However, generally the results of human and rodent studies have been contradictory and the mechanisms surrounding the metabolic effects of CLA are not fully understood.
Researchers1 have compared the effects of two CLA Supplements on the total and regional fat mass in healthy post menopausal women. Subjects were fed either 5.5 grams per day of a supplement containing a mixture of 40% cis-9 trans-11 and 40% trans-10 cis-12 CLA, a supplement containing 4.7 grams per day of cis-9 trans-11 CLA, or a control supplement of olive oil (4.2 grams per day of oleic acid). At baseline the mean weight and fat mass of all groups was identical, however after 16 weeks on the supplements the subjects taking the mixture of two CLA isomers had less total fat mass (4%) and less lower body fat mass (7%) than the control subjects and the subjects taking the cis-9 trans-11 CLA isomer. The weight of the subjects taking the CLA mix was also 0.8kg lower than the subjects in the other two groups.
These results suggest that the trans-10 cis-12 isomer may be responsible for the weight loss effect of CLA because in this study, reductions in fat mass and weight loss were not seen with the cis-9 trans-11 isomer in isolation. Interestingly, those subjects taking the CLA mix supplement had an increase in their serum insulin levels, which support findings from previous human studies that suggests that CLA may have a negative effect of insulin metabolism. Mice fed a mixture of cis-9 trans-11 and trans-10 cis-12 CLA showed a decrease in insulin sensitivity, but rats fed the same mixture had an increase in sensitivity. The increase increased serum insulin concentrations were greatest in the subjects in the highest waist circumference tertile, suggesting that the negative effects of CLA on insulin metabolism are most pronounced on those subject with symptoms of the metabolic syndrome.
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