The most biologically effective products contain a chitosan fraction having a low molecular weight. Unfortunately, not every clinical study indicates whether low molecular weight chitosan has been used. Therefore, aside from the usual variables, discrepant results may be due to differences in the type of chitosan used. WEIGHT LOSS
Chitosan is widely marketed as a weight-loss aid, primarily due to its ability to bind to fats and reduce their absorption in the digestive tract.
A Cochrane systematic review published in 2005 analysed the results of 14 randomised studies involving 1131 subjects and concluded that use of chitosan resulted in a significantly greater weight loss, decrease in total cholesterol and decrease in systolic and diastolic blood pressure than placebo (Ni et al 2005). The studies had a minimum duration of 4 weeks and were conducted with overweight or obese subjects. In regards to the frequency of adverse events or faecal fat excretion, no clear differences were observed between the placebo and chitosan groups. Although encouraging, the authors noted that the quality of the studies was suboptimal and overall results were variable. A look at the studies of highest quality suggests that the effects are minimal. The mean trial duration was 8.3 weeks (range 4-24 weeks) and 8 of the 14 studies combined the use of chitosan or placebo with a low-calorie or weight-reducing diet. Interpretation of the data is not straightforward because the dose of chitosan used in studies varied considerably, from 0.24 g/day to 1 5 g/day (mean 3.7 g/day) and six of the studies used treatment preparations that contained other active ingredients in addition to chitosan. Additionally, the review excluded some potentially important trials because they did not meet criteria for © 2007 Elsevier Australia
inclusion (e.g. subjects were not enrolled for being overweight but selected for other reasons).
Previously, a 1998 meta-analysis identified five studies evaluating the effectiveness of chitosan for the treatment of obesity (Ernst & Pittler 1998). All studies included were conducted in Italy and published in a single Italian journal over a 2-year period. They concluded that the mean difference in terms of weight reduction between chitosan and placebo was approximately 3.3 kg. It is worth noting that these five studies consistently demonstrated the greatest effects in the 2005 Cochrane systematic review discussed above, were all of short duration, and four of them also included other agents in the chitosan preparations.
A later systematic review conducted by Ernst and Pittler, which included five additional studies, concluded that when these new results were combined with the previous five from the 1998 meta-analysis, the evidence becomes less compelling and raised doubts about the effectiveness of chitosan in weight loss (Pittler & Ernst 2004).
Clearly, further well-reported research is required, using longer time frames and clearly stating the composition of the chitosan preparations.
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