Researchers in Germany tested nine such products against placebo pills in one of the most extensive trials of weight loss supplements ever conducted.
They found that the supplements were no more effective than the dummy pills for promoting weight loss during the eight-week study.
The investigators say the findings show the importance of subjecting supplements marketed for weight loss to rigorous scientific research to determine if they have any benefit.
The study was presented today in Stockholm at the International Congress on Obesity.
Billions Spent on Weight Loss Supplements
Europeans spend about $1.4 billion a year on unregulated weight loss supplements and Americans spend about $1.6 billion a year on the products, researcher Igho Onakpoya, MSc, says.
In a review of the limited research on the dietary supplements, Onakpoya and colleagues from the universities of Exeter and Plymouth in the U.K. found little evidence that any of the widely sold, unregulated products they tested promoted weight loss.
"The only thing these supplements effectively help people lose is their money," Onakpoya tells WebMD.
The only tested supplements found to promote weight loss were those containing ingredients shown to pose a health risk, such as ephedra, which was banned in the U.S. in 2004 following a series of heart-related deaths linked to products containing the stimulant.
Study Included So-Called 'Fat Blockers'
The nine weight loss supplements tested in the German study included the active ingredients L-carnitine, polyglucosamine, cabbage powder, guarana seed powder, bean extract, Konjac extract, fiber, sodium alginate, or selected plant extracts either alone or in combination.
These ingredients have been marketed for promoting weight loss in a number of ways. Guarana seed, which is found in many of the weight loss supplements sold over the counter in the U.S., is said to be an appetite suppressant and energy booster. L-carnitine is said to promote muscle growth while burning fat.
The polyglucosamine protein chitosan, which is commonly derived from the shells of crabs, shrimp, and other shellfish, is also a popular ingredient in weight loss supplements. Products containing chitosan are generally marketed as dietary fat blockers.
Study researcher Thomas Ellrott and colleagues from Germany's University of Gottingen Medical School enrolled 189 obese or overweight middle-aged people who agreed to take a weight loss supplement for eight weeks. Half took commercially available supplements and half took the dummy pills.
No Meaningful Difference in Weight Loss
The over-the-counter supplements were purchased from area pharmacies, but the researchers changed their packaging and product names to make them indistinguishable from the placebo pills.
Some of the products included dietary advice in their instructions, so the researchers rewrote the instructions to include the advice without mentioning the product name.
After eight weeks, people taking the commercial supplements had lost an average of 2 to 4 pounds compared to an average loss of 2 and 1/2 pounds in the placebo group, but the difference could have been a chance finding.
Weight loss supplements like the ones tested in the study are not regulated and their claims do not have to be proven in clinical trials.
The research was supported by funding from the German consumer magazine Justice. No other funding sources were reported.
Researcher: 'Buyer Beware'
Weight loss supplement researcher Judith Stern, ScD, tells WebMD that she knows of no unregulated supplements that promote weight loss and keep weight off.
She says studies of several years' duration would be needed to prove the effectiveness of a dietary supplement or drug marketed for weight loss.
"If you tell someone a pill will help them lose weight and you motivate them to do it, many people will lose weight," she says. "But it is impossible to know if the pill caused the weight loss."
Stern's own research examining chitosan-containing supplements found no support for the claim that the products "trap" dietary fat and excrete them from the body.
"If these supplements worked I would be the first person to recommend them," she says. "But the claims on the labels are just that and the manufacturers don't have to prove them. My message to the public is caveat emptor: Let the buyer beware."
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.