Chitosan is a fibre extracted from chitin, which is a structural component of crustacean shells, crabs, shrimps and lobsters. Chitin is de-acetylated to produce chitosan.
Chitosan is a polysaccharide containing numer-ous acetyl groups.
Chitosan binds fat molecules as a result of its ionic nature. When taken orally, chitosan has been reported to be able to bind 8–10 times its own weight in fat from food that has been consumed. This prevents fat from being absorbed and the body then has to burn stored fat, which may lead to reductions in body fat and body weight.
In mice treated with chitosan and given a high-fat diet, chitosan prevented the increase in body weight, hyperlipidaemia and fatty liver normally induced by such a diet. In a randomised, placebo-controlled, double-blind study, 34 overweight human volunteers were given four capsules of chitosan or placebo for 28 consecutive days. Subjects maintained their normal diet and documented their food intake. After 4 weeks of treatment, body mass index, serum cholesterol, triglycerides, vitamin A, D and E and beta-carotene were not significantly different in the two groups. The results suggest that chitosan in the dose given had no effect on body weight in overweight subjects. No serious adverse effects were reported.
In another placebo-controlled, double-blind study, 51 healthy obese women were given chitosan 1200 mg twice a day for 8 weeks. No reductions in weight were observed in any treatment group. LDL cholesterol fell to a greater extent in the chitosan group than the placebo group, but there was no significant change in HDL cholesterol and triglycerides were slightly increased.
A 24-week randomised, double-blind, placebo-controlled trial involving 250 obese women found that the chitosan group lost more weight than the placebo group but the effects were very small. A systematic review of 14 RCTs involving a total of 1071 participants found that weight loss in high-quality studies was less than in lower quality studies. The review concluded that the effect of chitosan on body weight is minimal and unlikely to be of clinical significance.
Chitosan reduced blood glucose and cholesterol in an animal model of lean-type non-insulin-dependent diabetes mellitus with hypoinsulinaemia, but had no effect in an animal model of obese-type NIDDM with hyperinsulinaemia. The authors concluded that chitosan could be a useful treatment for lean-type NIDDM with hypoinsulinaemia. Two recent double-blind RCTs in humans investigating the effect of chitosan on plasma cholesterol have shown conflicting results. One was a Japanese study involving 90 women with mild to moderate hypercholesterolaemia, which found that chitosan significantly reduced cholesterol although the effect was small. The second was a Finnish study in 130 men and women with moderately increased plasma cholesterol, which found that chitosan had no effect on the concentrations of plasma lipids or glucose.
Chitosan should be avoided in patients with gastrointestinal malabsorption conditions.
Pregnancy and breast-feeding
No problems have been reported, but weight loss should not be attempted during pregnancy.
There are no long-term studies assessing the safety of chitosan. However, chitosan may reduce the absorption of fat-soluble vitamins (A,D, E and K). This has been shown in animals,7 but not in humans.2,3
Chitosan is available in the form of tablets and capsules.
The dose is not established. Dietary supplements provide 1500–3000 mg per daily dose.
Chitosan is promoted for weight loss, but there have been few trials, and results have been conflicting. Any effect of chitosan on body weight is likely to be very small. Chitosan has also been investigated for an effect on plasma cholesterol, but the effects are likely to be very small, if any.
Dietary Supplements, Third Edition, by Pamela Mason, BSc, MSc, PhD, MRPharmS, published by Pharmaceutical Press, London, 2007.
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Mhurchu CN, Poppitt SD, McGill AT, et al. The effect of the dietary supplement, chitosan, on body weight: a randomised controlled trial in 250 over-weight and obese adults. Int J Obes Relat Metab Disord 2004; 28: 1149–1156.
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Miura T, Usami M, Tsuura Y, et al. Hypoglycemic and hypolipidemic effect of chitosan in normal and neonatal streptozotocin-induced diabetic mice. Biol Pharm Bull 1995; 18: 1623–1625.
Deuchi K, Kanauchi O, Shizukuishi M, et al. Contin-uous and massive intake of chitosan affects soluble vitamin status in rats fed on a high fat diet. Biosci Biotech Biochem 1995; 59: 1211–1216.
Bokura H, Kobayashi S. Chitosan decreases total cholesterol in women: a randomized, double-blind, placebo-controlled trial. Eur J Clin Nutr 2003; 57: 721–725.
Metso S, Ylitalo R, Nikkila M, et al. The effect of long-term microcrystalline chitosan therapy on plasma lipids and glucose concentrations in subjects with increased plasma total cholesterol: a ran-domised placebo-controlled double-blind crossover trial in healthy men and women. Eur J Clin Pharma-col 2003; 59: 741–746.