Efficacy and safety of dietary supplements containing CLA for the treatment of obesity

Abstract

Dietary supplements containing conjugated linoleic acid (CLA) are widely promoted as weight loss agents available over the counter and via the Internet. In this review, we evaluate the efficacy and safety of CLA supplementation based on peer-reviewed published results from randomized, placebo-controlled, human intervention trials lasting more than 4 weeks. We also review findings from experimental studies in animals and studies performed in vitro. CLA appears to produce loss of fat mass and increase of lean tissue mass in rodents, but the results from 13 randomized, controlled, short-term ( Ͻ 6 months) trials in humans find little evidence to support that CLA reduces body weight or promotes repartitioning of body fat and fat-free mass in man. However, there is increasing evidence from mice and human studies that the CLA isomer trans -10, cis -12 may produce liver hypertrophy and insulin resistance via a redistribution of fat deposition that resembles lipodystrophy. CLA also decreases the fat content of both human and bovine milk. In conclusion, although CLA appears to attenuate increases in body weight and body fat in several animal models, CLA isomers sold as dietary supplements are not effective as weight loss agents in humans and may actually have adverse effects on human health. Conjugated linoleic acid (CLA) is a collective term used to describe the mixture of positional and geometric isomers of linoleic acid with conjugated double bonds (i.e., the two double bonds are separated by one single bond).

The role of conjugated linoleic acid in reducing body fat and preventing holiday weight gain

“…25 We did not see a change in liver function tests including AST, ALT, ALP and total bilirubin. Of six recent studies including similar measures of liver function, only Gaullier et al 10,11 showed significant within-group increases in AST.…”

“…Although some animal studies have shown negative effects with CLA, this is possibly attributable to greater doses: animals often receive 10-50 times the dosage per unit body weight compared to humans. 25 The effect of CLA on blood glucose and insulin sensitivity is controversial, Effect of CLA on body weight and composition AC Watras et al although reported deleterious effects appear to be primarily related to the trans-10, cis-12 CLA isomer. 6 Riserus et al…”

“…25 In humans, however, the majority of studies have shown that supplementation with CLA mixtures does not have an effect on plasma cholesterol or TG levels compared to controls. 5 Similarly, we found no difference between groups in the change in total cholesterol, LDL, HDL or TGs.…”

Impact of dietary betaine and conjugated linoleic acid on insulin sensitivity, protein and fat metabolism of obese pigs

“…Although there is some evidence from mice and human studies that the CLA isomer trans-10, cis-12 may produce liver hypertrophy and insulin resistance via a redistribution of fat deposition that resembles lipodystrophy (Larsen et al, 2003), the CLA-induced changes in glucose tolerance and liver metabolism observed in the various animal studies are conflicting. For example, dietary CLA has been reported to decrease TG accumulation in the liver of Wistar rats (Purushotham et al, 2007), but hyperinsulinaemia was observed in wild-type mice supplemented with CLA (Tsuboyama-Kasaoka et al, 2000).…”

“…Furthermore, there is little information on how betaine and CLA affect serum hormone and metabolite profile. In addition, some deleterious effects have been reported when CLA was fed to laboratory animals, such as insulin resistance, liver enlargement and hepatic steatosis (Larsen et al, 2003). Thus, the effect of dietary CLA on liver function needs to be researched in non-rodent models.…”