Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of the essential fatty acid linoleic acid (LA, C18:2 (n-6)). Evidence suggests that conjugated linoleic acid may be beneficial in obesity because it causes weight loss. However, this benefits seems to relate only to certain isomers, whereas others show no effect. Milk and other dairy products contain CLA because fermentative bacteria can produce it in the rumen of sheep. It is theorised that the CLA in milk and cheese may be responsible for some of the weight loss effects of increased dairy intake. The most common CLA isomers in ruminant products are the cis-9, trans-11 and trans-10, cis-12 isomers, which make up the bulk of the CLA in the human diet. Some evidence from animals studies suggests that CLA may have beneficial effects on diabetes, but as with weight loss this might be isomer specific.
Because of the possible beneficial effects of CLA on diabetes and insulin resistance, researchers have investigated the association between CLA and the prevalence of diabetes. For example, in one study1 researchers analysed the adipose tissue of 232 diabetic and 1512 non-diabetic subjects for isomers of CLA in order to investigate if an association existed. The cis-9, trans-11 isomer of CLA made up 0.57 % of the total fatty acid content of adipose tissue in subjects without diabetes and 0.53 % in those with diabetes. The cis-9, trans-12 isomer of CLA was also significantly associated with a lower risk of diabetes. The prevalence ratio of diabetes for the fifth quintile compared to the first quintile for the concentration of the cis-9, trans-12 isomer of CLA was 0.48. However, the trans-10, cis-12 isomer of CLA was not detected in the adipose tissue of either group of subjects.
These results suggests that higher concentrations of CLA in the adipose tissue are associated with a lower risk of diabetes. Because the fat content of adipose tissue reflects dietary intake, this may suggest that dietary intakes of CLA are protective of diabetes. The presence of the cis-9, trans-12 isomer, but absence of the trans-10, cis-12 isomer might be explained by their relative concentrations in the diets of humans. The cis-9, trans-12 isomer is present in the human diet in relatively high concentrations and makes up around 80 % of CLA intake. In contract the trans-10, cis-12 isomer makes up only around 10 % of intake. If CLA in adipose tissue is inversely associated with the prevalence of diabetes, this may explain the weight loss effects of diary products. Conjugated linoleic acid may be protective of diabetes because it may increase glucose-stimulated insulin secretion by activating the free fatty acid receptor 1 or may increase insulin production.
RdB
