Dietary supplement chitosan shows some promise in treating obesity

Aug 23 2005

The dietary supplement chitosan shows some promise in treating overweight and obesity but has not been shown conclusively to be an effective weight loss aid, according to a new systematic review of current evidence.

The review assessed results of 14 randomized controlled trials that included 1,131 overweight or obese adults. Those who received chitosan (pronounced kigh-toh-san) had an average weight loss of almost 4 pounds more than those on placebo in the short term, and their cholesterol and blood pressure levels also decreased more than those in the placebo group. There were no side effects noted in the group taking chitosan.

"This review has indicated that chitosan may be an effective aid to weight loss but many of the included trials have been limited by poor methodology and reporting," according to lead author Cliona Ni Mhurchu, Ph.D., of the University of Auckland in New Zealand, and colleagues.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

The average age of participants in the chitosan study was 44 years. Eleven of the studies included both men and women; three included women only. The study subjects were given either chitosan (doses ranged from less than a quarter of a gram to 15 grams a day) or a placebo for a short-term period of four weeks, medium-term period of less than six months or a long-term period of at least six months.

According to the background information from the National Institute of Environmental Health Sciences, Chitosan (marketed also as chitopearl and chitin) was popularized as a weight loss aid by the 1997 book The Fat Blocker Diet. Chitosan is readily available in alternative medicine outlets and over the Internet. The supplement is derived from chitin, which is found the in the shells of shrimp, lobster and crab.

"There is cheap and easy access to over-the-counter treatments," Ni Mhurchu notes, "and many people have the perception that herbal or natural remedies are safer than prescription medication."

Adding medication to diet and lifestyle changes has been shown to improve long-term weight loss, but not all patients are willing to take prescription medication to lose weight. "Research indicates that people take dietary supplements for a variety of reasons," says Carol Haggans, a scientific and health communications consultant with the Office of Dietary Supplements at the National Institutes of Health.

"For weight loss specifically, it is likely that people take supplements instead of medications because prescription medications are reserved for people who are severely overweight," Haggans says. "People tend to want to find a quick fix for weight loss, but the best way to lose weight is to eat fewer calories and increase physical activity."

"The manufacturers of supplements and herbal products should be obliged to provide evidence of efficacy before putting them on the market," Ni Mhurchu says. "People mistakenly believe that the manufacturers do have to prove the efficacy of the product and therefore think they are effective. The perception that such products are safer than prescription medication is wrong; there is a risk without adequate safety and monitoring regulations."

Ni Mhurchu concludes that "better trials of chitosan will not necessarily show positive results, but I think they will show more clearly if the product does or does not have an effect on body weight."

Three of the four study authors were investigators in one of the trials included in the review. The Health Research Council of New Zealand provided most of the funding for that trial; additional funding came from a manufacturer of chitosan.