The Claim: C.L.A. Supplements Can Help You Lose Weight

THE FACTS

It has been called a miracle pill, able to help you shed fat, lose weight and build muscle. It can be found in health food stores all over, but is C.L.A. - also known as conjugated linoleic acid - all it's cracked up to be?

Discovered more than two decades ago, the substance is popular among dieters and body builders, and reportedly reduces body fat gain and enhances lean body mass. Over the years, a number of studies have found that C.L.A., unlike many other supplements, may actually help users trim fat. But it also carries side effects.

The most recent study was published this month in The American Journal of Clinical Nutrition. The report, a meta-analysis that pooled the results of more than a dozen randomized studies, found that people who took 3.2 grams of C.L.A. a day showed a drop in fat mass of about 0.2 pounds a week - or nearly a pound a month - compared with those given a placebo. The researchers, at the University of Wisconsin School of Medicine, concluded that the supplement "produces a modest loss in body fat in humans."

But other studies have hinted at serious adverse health effects. Researchers have found that it can increase blood levels of C-reactive protein, lipoprotein and leptin - all of which can heighten the risk of heart disease. There is also some evidence that taking C.L.A. daily increases insulin resistance, a sign of impending Type 2 diabetes.

THE BOTTOM LINE

Studies have found that C.L.A. supplements can produce slight reductions in body fat, but that it may carry health risks.

scitimes@nytimes.com