Background: Conjugated linoleic acid (CLA) has been shown to be an effective supplement for reducing fat mass in animals, whereas results in humans have been inconsistent.

Objective: This is a meta-analysis of human studies in which CLA was provided as a dietary supplement to test its efficacy in reducing fat mass.

Design: We searched the PubMed database (National Library of Medicine, Bethesda, MD) and references from the resulting search to identify studies in which CLA was provided to humans in randomized, double-blinded, placebo-controlled trials and in which body composition was assessed by using a validated technique.

Results: We identified 18 eligible studies. Of these, 3 were single-isomer studies, and results comparing CLA isomers were inconclusive. We compared the length of treatment by using studies in which a mixture of purified isomers were used and those in which purified trans-10,cis-12 isomers were used. This comparison indicated that the effect of CLA was linear for up to 6 mo and then slowly approached an asymptote at 2 y. An analysis of the dose effect indicated that fat loss compared with placebo was -0.024 kg x g CLA(-1) x wk(-1) (P=0.03). After adjustment to the median dose of 3.2 g CLA/d, CLA was effective and produced a reduction in fat mass for the CLA group alone (0.05 +/- 0.05 kg/wk; P<0.001) and for the CLA group compared with placebo (0.09 +/- 0.08 kg/wk; P<0.001)

Conclusion: Given at a dose of 3.2 g/d, CLA produces a modest loss in body fat in humans.