Conjugated linoleic acid (CLA) is the name given to a group of isomers of linoleic acid [18:2(n-6)] that are popular in dietary supplements because of their role in the regulation of adiposity and insulin sensitivity. Conjugated linoleic acid is found mainly in the meat and dairy products of ruminants (e.g. mutton and beef) and contains both a trans and a cis double bond separated by a single bond (figure 1). Evidence suggests that the trans-10, cis-12 isomer can prevent the development of obesity in animal models, although the effects on insulin resistance, diabetes, obesity and adiposity in human studies are not so clear. Early work using mice showed that conjugated linoleic acid regulated body composition and this work has been replicated consistently. However, studies using humans have not shown the same results.
Figure 1. The structure of linoleic acid and trans-10, cis-12 conjugated linoleic acid
One theory suggests that trans-10 and cis-12 CLA works to control weight because it inhibits the differentiation of human preadipocytes into mature insulin‑sensitive adipocytes1. It is thought that this occurs because CLA can rinhibit the PPARγ transcription factor and therefore affect its downstream targets that are critical for fatty acid and glucose metabolism. By reducing the expression of PPARγ in developing preadipocytes, trans-10, cis-12 CLA may result in the formation of a fibroblast-like cell that has some of the characteristics of an adipocyte, i.e. that it can express leptin, but which has significantly decreased insulin sensitivity and ability to store triglycerides. The inconclusive results in human trials might be as a result of the use of mixed isomers that interfere and negate the effects of the biologically active trans-10 and cis-12 CLA isomers necessary for the regulation of adiposity
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