Conjugated linoleic acid (CLA), a specialized type of fatty acid with a slightly different structure than typical fats in the diet, has been marketed as a weight loss supplement based on impressive animal data showing it enhances fat loss. Less work has been done in humans. In one study, overweight men and women were assigned to receive either a placebo or one of five different doses of CLA for a 12-week period. Subjects who consumed 3.4 g CLA per day lost significantly more fat (-3.8 lbs) than the placebo group (+3.2 lbs). There was no additional benefit of taking more than 3.4 g CLA per day.
Another study in humans examined the effects of CLA supplementation on body composition and strength during 28 days of resistance training in experienced lifters. In contrast to the earlier study, no significant differences were noted in either fat or lean body mass between the CLA and the placebo group. However, there was a strong trend for a greater increase in bone mass in the CLA group. Increases in bone mass have been observed in animal studies as well. This was a relatively short study (28 days) and the favorable effect in fat mass may have occurred over a longer supplementation period.
Considering the many other possible health benefits of CLA including increased bone mass, increased antioxidant activity, anti-cancer properties, and immuno-enhancing activity there should certainly be more research examining the effects of CLA in humans to validate earlier animal and human work.