Background: CLA (conjugated linoleic acid) supplements are advertised as a way to reduce weight and to obtain a "better balance between fat and muscle". What evidence is there for these health claims, and is CLA supplementation safe and without adverse effects?
Material and methods: This review is based on peer-reviewed scientific publications.
Results: Large doses of CLA supplements in rodents reduce fat mass and increases muscle mass, but the results from 13 randomised, placebo-controlled clinical studies do not support these findings with regard to humans. However, results from both animal and human studies indicate that the CLA isomer 10-trans,12-cis may have a negative impact on carbohydrate and lipid metabolism by inducing insulin resistance and hyperlipidaemia. Studies of CLA supplementation to lactating women have revealed lower fat content in their milk. Furthermore, the cordial blood concentration of CLA in women has been shown to correlate negatively with both gestational length and birth weight.
Conclusion: Even if reduced weight and fat mass has been observed in animal models following CLA supplementation, the basis is, at best, weak for such claims in humans. Provided that the fat mass reducing effect of CLA is mediated through PPARgamma, this may result in adverse metabolic effects.