Chitosan
A fibre-like compound derived from the shells of shellfish (shrimp, crab, lobster). Sold as a 'fat binder' — the idea is that it binds to dietary fat in the gut and prevents some of it from being absorbed. The evidence shows modest weight loss in studies. Important: not suitable for anyone with a shellfish allergy.
Quick read · 3 min
- •Evidence: Moderate — some consistent evidence but with limitations
- •A 2023 network meta-analysis of 111 randomised controlled trials found that chitosan produced 1.
- •Generally well-tolerated.
- •Unlike prescription drugs, supplements are not tested for effectiveness by the FDA before sale
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: March 2026
How it works
Chitosan carries a positive electrical charge that attracts and binds to negatively charged fat molecules in the digestive tract, forming a gel-like complex that passes through the gut without being absorbed. This reduces the amount of dietary fat your body takes in — similar in concept to prescription orlistat but considerably weaker in effect.
What the evidence shows
A 2023 network meta-analysis of 111 randomised controlled trials found that chitosan produced 1.70 kg more weight loss than placebo — moderate certainty evidence. This was consistent with an older Cochrane review of 15 randomised controlled trials (1,219 participants) which found 1.7 kg more weight loss than placebo. The evidence is reasonably consistent, but the magnitude of effect is modest.
Safety
Generally well-tolerated. The most common side effects are GI-related: constipation, bloating, and stomach discomfort. IMPORTANT: chitosan is derived from shellfish shells. Anyone with a shellfish allergy should avoid chitosan entirely — allergic reactions are possible. Chitosan may reduce absorption of fat-soluble vitamins (A, D, E, K) and some medications — talk to a pharmacist or doctor if you take other medicines.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“If you have any shellfish allergy, don't use this. The shellfish origin is right on the label but it's easy to miss if you're not looking for it.”
“It works better with high-fat meals — that's when there's more fat for it to bind. Doesn't do much if you're already eating low-fat.”
Common questions
After reading this page, most people compare this with other supplements, look at prescription options, or check what they can do today without a prescription.