April 1, 2005 -- It sounds too good to be true but an increasing number of Americans are buying into the notion that a dietary supplement called conjugated linoleic acid, or CLA, can help them both lose weight and increase muscle mass.
A new study funded by the leading manufacturer of CLA suggests just that. But experts tell WebMD that the claims about the supplement far outweigh the science. The researcher who discovered CLA says that while it can help people replace fat with muscle, it is no miracle weight loss aid.
"I have been telling people for years that this is not a weight loss product," Michael W. Pariza, PhD, tells WebMD. "If someone takes CLA to lose weight but doesn't change their diet or exercise patterns they are going to be disappointed."
CLA is a natural occurring fatty acid found in meats and dairy products, with claims of helping people lose fat, maintain weight loss, retain lean muscle mass, and control type 2 diabetes -- the type of diabetes that is often associated with obesity.
Early animal studies following its identification by Pariza and colleagues in the late 1970s raised hopes that it could be used to fight human cancer.
The popular dietary supplement is now sold in health food stores and on the Internet.
In a study published last Maystudy published last May involving 180 people who were overweight, those who took CLA for a year lost between 7% and 9% of their body fat even though they did not change their lifestyles or eating habits.
But CLA users lost only a modest amount of weight -- 4 pounds during the yearlong study. And the investigation did little to silence concerns about the long-term safety of the supplement. The volunteers taking CLA had changes in certain heart disease risk factors.
CLA users had slightly higher LDL "bad" cholesterol and slightly lower HDL "good" cholesterol than nonusers. And the CLA group had higher white blood cell counts and lipoprotein (a) levels -- also known as lipoprotein little (a). Both are markers of inflammation linked to heart disease.
In this follow-up study, 134 of the overweight participants either continued taking CLA for another year or could start taking the supplement if they had been in the placebo group. Both groups took 3.4 grams of CLA a day and continued their normal lifestyle habits. They ate what they wanted without restricting calories and continued their usual amounts of physical activity.
The study was funded by the company that markets Tonalin CLA, the largest selling brand of the supplement. The findings are reported in the April 1 issue of The Journal of Nutrition.
The group that had already been taking CLA lost no more weight or body fat, but they maintained the body fat losses seen in the previous year. People who began taking the supplement during year two of the study lost an average of 3.5 pounds and also saw reductions in overall body fat.
The safety picture for those who took the supplement for two years was somewhat reassuring. Total cholesterol and LDL cholesterol were reduced slightly, while HDL cholesterol, triglycerides, and fasting blood glucose levels remained unchanged.
But there were consistent increases in lipoprotein levels associated with CLA use. Lipoprotein levels are believed to be independent predictors of heart disease risk.
CLA use was also associated with increases in white blood cells and blood platelet counts, which suggested an inflammatory response to use of the supplement. Inflammatory responses like these are believed to lead to blood vessel damage seen in atherosclerosis and cardiovascular disease.
Researcher Jean-Michel Gaullier and colleagues concluded that the role of CLA in cardiovascular risk is still "equivocal."
"Further studies are needed to determine if there is an effect of CLA on cardiovascular risk and inflammation in humans," they wrote.
In a review of the CLA research, published last year, California nutritionists Lisa Rainer, MS, RD, and Cynthia J. Heiss, PhD, concluded that while the animal studies on CLA are promising, the research in humans remains inconclusive.
"The existing studies of CLA supplementation in human beings are difficult to interpret because of the different parameters measured and the variances in dosage, duration of administration, and subject characteristics," they write.
In an interview with WebMD, Rainer said she would not recommend CLA supplementation for weight control on the basis of the studies she has seen.
"More trials need to be done in human beings before we really know the long-term benefits and safety," she says.
But Pariza, who began taking CLA when it became available in supplement form almost a decade ago, believes strongly that long-term use by healthy people is not only safe but beneficial.
He says CLA may have merit as a weight loss supplement when combined with another weight-reducing treatment or may singularly promote loss of body fat and maintenance of muscle. He says the supplement also can subsequently reduce the risk of weight regain.