Benefits
Modest fat absorption reduction
Chitosan's positive charge binds negatively charged dietary fatty acids in the acidic stomach, forming a viscous gel that passes into the small intestine partially resisting lipase digestion. What that adds up to in practice is very little. The 2008 Cochrane review of 15 randomised trials in 1,219 people concluded that results from high quality trials indicate the effect of chitosan on body weight is minimal and unlikely to be of clinical significance. When the analysis was restricted to the better concealed, larger or longer trials, those trials produced substantially smaller decreases in weight. In other words, the better the trial, the smaller the effect. A 2018 meta-analysis of 14 trials was more favourable but still described the effect as slight.
Cholesterol reduction
By binding bile acids and dietary cholesterol in the GI tract, chitosan reduces cholesterol absorption and enterohepatic bile acid recirculation. The measured changes, though, are small and not consistent. The 2018 meta-analysis of 14 randomised trials reported only a slight improvement in blood fats, and the Cochrane review found that the higher quality trials produced substantially smaller decreases in total cholesterol than the weaker ones. No specific LDL figure can be promised from this evidence.
Blood pressure support
Blood pressure was one of the measures pooled in the 2018 meta-analysis of 14 randomised trials, which described the overall effect on weight, blood fats and cardiovascular factors as slight. Those were weight loss trials, not blood pressure treatment trials, and chitosan is not a treatment for high blood pressure. Explanations such as reduced sodium absorption or ACE inhibition by chitosan fragments come from laboratory work, not from anything these trials measured.
Wound dressings are a different product, not this supplement
Chitosan is also used in bandages and dressings that are placed on the skin to help stop bleeding, and some of those are regulated medical devices. That is a completely different product from a chitosan capsule, and none of it is a benefit of swallowing chitosan. Neither of the two studies cited on this page looked at wounds.
Mechanism of action
Electrostatic fat binding via positive charge
Chitosan's free amino groups are protonated in the acidic stomach environment, creating a strongly cationic polymer. Dietary fatty acids (negatively charged carboxylate groups) electrostatically bind to chitosan, forming a viscous complex that is thought to partially resist pancreatic lipase digestion in the small intestine and to reduce how much fat is absorbed. This is the proposed mechanism. The trials that actually measured weight and cholesterol found the real world effect to be small.
Bile acid sequestration and cholesterol reduction
Like other dietary fibers, chitosan binds bile acids in the intestinal lumen, preventing their reabsorption. Hepatic cholesterol is then converted to new bile acids, reducing serum cholesterol and increasing LDL receptor expression. The idea that chitosan's positive charge binds bile acids better than neutral fibers comes from laboratory work, not from the two human reviews cited here, and the cholesterol changes those reviews measured were small.
Prebiotic and microbiome modulation
Chitosan that escapes fat binding is fermented by colonic bacteria, producing short-chain fatty acids and selectively feeding Bifidobacterium populations. This prebiotic idea comes from laboratory and animal research. Neither of the human reviews cited on this page measured gut bacteria or short chain fatty acids, so treat it as unproven in people.
Clinical trials
Cochrane systematic review and meta-analysis of 15 randomised controlled trials in 1,219 participants, examining chitosan for overweight and obesity. (Cochrane Database Syst Rev, 2008)
1,219 participants pooled across 15 randomised trials in overweight or obese adults.
The reviewers found some evidence that chitosan beats placebo for short term weight loss, but also that many of the trials were of poor quality and the results were variable. Their conclusion was blunt: results from high quality trials indicate that the effect of chitosan on body weight is minimal and unlikely to be of clinical significance. When the analysis was restricted to trials that were properly concealed, larger or longer, those trials produced substantially smaller decreases in weight and total cholesterol. The better the trial, the smaller the effect.