Chitosan for overweight or obesity

Chitosan, a deacetylated chitin, is a dietary supplement reported to decrease body weight. It is widely available over the counter worldwide and although evaluated in a number of trials its efficacy remains in dispute.

To assess the effects of chitosan as a treatment for overweight and obesity.

We searched electronic databases (MEDLINE, EMBASE, BIOSIS, CINAHL, The Cochrane Library), specialised web sites (Controlled Trials, IBIDS, SIGLE, Reuter's Health Service, Natural Alternatives International, Pharmanutrients), bibliographies of relevant journal articles, and contacted relevant authors and manufacturers. Last searches were completed in March 2004.

Trials were included in the review if they were randomised controlled trials of chitosan a minimum of four weeks duration in adults who were overweight or obese. Authors of included studies were contacted for additional information where appropriate.

Details from eligible trials were extracted independently by two reviewers using a standardised data extraction form. Differences in data extraction were resolved by consensus. Continuous data were expressed as weighted mean differences and standard deviations. The pooled effect size was computed by using the inverse variance weighted method.

Fourteen trials including a total of 1131 participants met the inclusion criteria. No trial to date has measured the effect of chitosan on mortality or morbidity. Analyses including all trials indicated that chitosan preparations result in a significantly greater weight loss (weighted mean difference -1.7 kg; 95% confidence interval (CI) -2.1 to -1.3 kg; P < 0.00001), decrease in total cholesterol (-0.2 mmol/L; 95% CI -0.3 to -0.1; P < 0.00001), decrease in systolic (-5.9 mmHg; 95% CI -7.3 to -4.6; P < 0.0001) and diastolic (-3.4 mmHg; 95% CI -4.4 to -2.4; P < 0.00001) blood pressure compared with placebo. There were no clear differences between intervention and control groups in terms of frequency of adverse events or in faecal fat excretion. However, the quality of many studies was sub-optimal and analyses restricted to studies that met allocation concealment criteria, were larger, or of longer duration showed that such trials produced substantially smaller decreases in weight and total cholesterol.

There is some evidence that chitosan is more effective than placebo in the short-term treatment of overweight and obesity. However, many trials to date have been of poor quality and results have been variable. Results obtained from high quality trials indicate that the effect of chitosan on body weight is minimal and unlikely to be of clinical significance.