Chitosan
Summary
Chitosan produces small short-term weight losses: about 1.7 kg versus placebo across 15 trials (1,219 people) in a Cochrane review, but the better-designed, larger and longer trials found substantially smaller effects (grade C). A controlled study found it trapped so little fat that losing one pound would need more than 7 months. Side effects are mostly mild digestive upset; it may raise warfarin's effect.
Key facts
- A polysaccharide made by deacetylating chitin from crustacean shells; some products use fungal chitosan[1][8]
- Body weight: about 0.9–1.7 kg extra loss (C); total cholesterol: small drop (C); fat excretion: clinically insignificant (D)[2][3][6]
- None set; chitosan is not a nutrient[1]
- Warfarin: a case report of a markedly raised INR that recurred on re-challenge[10]
- Flatulence, bloating, mild nausea, constipation, indigestion and heartburn[1]
- 6 graded human outcomes on this page
- October 10, 2026
How it works
ProposedChitosan is positively charged and is claimed to bind fats and bile acids in the gut, reducing their absorption. In a controlled feeding study, 2.5 g/day raised fecal fat by only 1.8 g/day in men and not at all in women, so fat trapping does not explain meaningful weight loss.[1][6]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Weight | Grade C | Improved | Meta-analysis of 15 trials · n = 1,219 · 2008 | 5 rows |
| Mechanism | Grade D | Mixed | Open-label · n = 24 · 2005 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Body weight, total cholesterol and blood pressure | Improved | Grade C | Meta-analysis · n = 1,219 · 2008 Adults with overweight or obesity in 15 RCTs Form: Chitosan preparations · Dose: Varied across trials · Duration: At least 4 weeks Weight fell 1.7 kg and total cholesterol 0.2 mmol/L more than placebo, with lower blood pressure. Trials with proper allocation concealment, larger samples or longer duration showed substantially smaller effects. Adverse events did not differ from placebo. | 18646097 (opens PubMed)Source [2] |
| Body weight, BMI and body fat | Improved | Grade C | Meta-analysis · n = 1,130 · 2020 Adults in 15 RCTs (18 treatment arms) Form: Chitosan · Dose: Varied; effects clearer above 2.4 g/day · Duration: Varied; effects clearer under 12 weeks Weight fell 0.89 kg, BMI 0.39 kg/m² and body fat 0.69% versus control. | 30990059 (opens PubMed)Source [3] |
| Body weight and body composition | Improved | Grade D | RCT · n = 96 · 2016 Adults with overweight or obesity, no diet change (India, multicentre) Form: Fungal-origin chitosan · Dose: 500 mg capsules, 5 per day (2.5 g/day) · Duration: 90 days The chitosan group lost a mean 1.78 kg by day 45 and 3.10 kg by day 90, significantly different from placebo (p<0.0001; the placebo change is not given in the abstract); body composition improved, lipids did not change and adverse events were mild. | 26747458 (opens PubMed)Source [8] |
| Body weight and BMI | Improved | Grade D | RCT · n = 80 · 2014 Women with overweight Form: Chitosan with or without vitamin C · Dose: 3 g/day chitosan (plus 2 g/day vitamin C in one arm) · Duration: 8 weeks Weight and BMI fell more than placebo in both chitosan groups, and adding vitamin C lowered BMI further (−1.6 vs −1.0 kg/m²). | 25835230 (opens PubMed)Source [9] |
| Body mass index and blood lipids | No effect | Grade D | RCT · n = 34 · 1999 Adults with overweight on their usual diet Form: Chitosan capsules · Dose: 4 capsules twice daily · Duration: 28 days BMI, cholesterol, triglycerides and vitamins A, D, E and beta-carotene did not differ from placebo; vitamin K rose in the chitosan group. | 10369493 (opens PubMed)Source [7] |
| Fecal fat excretion (fat trapping) | Mixed | Grade D | Open-label trial · n = 24 · 2005 Young adults (12 men, 12 women) on set diets Form: Chitosan capsules · Dose: 2.5 g/day before meals · Duration: 12 days (two 4-day collection periods) Fecal fat rose 1.8 g/day in men and did not change in women. The authors calculated men would need more than 7 months to lose one pound of fat. | 15635349 (opens PubMed)Source [6] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Chitosan from crustacean shells | Varies[1] | Claimed to act in the gut by binding dietary fat; no absorption data in our sources.[1] | Mild digestive side effects; theoretical concern in shellfish allergy.[1] | Most weight-loss trials |
| Fungal-origin chitosan | Varies[8] | No absorption data in our sources.[8] | Adverse events were mild in a 90-day trial.[8] | Indian 90-day weight trial (2.5 g/day) |
Studied doses
Doses studied in human trials ranged from about 2 to 3 g/day of chitosan, usually split before meals, for 4 weeks to 6 months. Pooled effects were clearer above 2.4 g/day and in trials shorter than 12 weeks.[1][3][8][9]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- WarfarinCase reportAn 83-year-old's INR rose markedly on chitosan 1,200 mg twice daily and rose again on re-challenge, probably from reduced vitamin K absorption. Avoid or monitor INR closely.[10]
Who should be careful
- Taking warfarin
- A documented case of raised INR, recurring on re-challenge, links chitosan to stronger warfarin effect.[10]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
How to read the label
- Label dose vs clinical doseTrials used about 2–3 g/day, taken as 5–8 capsules a day in the trials cited here.[1][8][9]
- "Blocks fat" claimsMeasured fat trapping was about 1.8 g/day in men and zero in women.[6]
- SourceCheck whether the chitosan is from shellfish or fungi if you have a shellfish allergy.[1][8]
Cost per studied dose, without the sales pitch
Compare any product you already have by the amount it delivers, not by capsule count or front-of-pack weight.
Cost per studied dose
Enter the price, servings and the amount per serving from your label.
Frequently asked questions
Does chitosan work for weight loss?
Slightly: pooled trials show about 1–2 kg more loss than placebo, but the best-designed trials found smaller effects that are probably not clinically meaningful.[2][3][4]
Does chitosan really block fat?
Barely. In a controlled study, 2.5 g/day trapped about 1.8 g of fat a day in men and none in women.[6]
Is chitosan safe with warfarin?
No: a case report documents a markedly raised INR that recurred when chitosan was restarted.[10]
Can I take chitosan with a shellfish allergy?
Shell-derived chitosan is a theoretical risk; fungal chitosan avoids it. A small study found no reactions to chitosan bandages in shellfish-allergic people.[1][11][8]
Does chitosan lower cholesterol?
The Cochrane review found a small drop in total cholesterol (0.2 mmol/L), but better-quality trials showed smaller effects.[2]
Sources
- [1]Dietary Supplements for Weight Loss: Fact Sheet for Health Professionals (updated May 18, 2022). NIH Office of Dietary Supplements, 2022. fact-sheet
- [2]Chitosan for overweight or obesity.. Cochrane Database Syst Rev, 2008. meta-analysis
- [3]The effects of chitosan supplementation on body weight and body composition: a systematic review and meta-analysis of randomized controlled trials.. Crit Rev Food Sci Nutr, 2020. meta-analysis
- [4]Efficacy of dietary supplements containing isolated organic compounds for weight loss: a systematic review and meta-analysis of randomised placebo-controlled trials.. Int J Obes (Lond), 2021. meta-analysis
- [5]A Meta-Analysis on Randomised Controlled Clinical Trials Evaluating the Effect of the Dietary Supplement Chitosan on Weight Loss, Lipid Parameters and Blood Pressure.. Medicina (Kaunas), 2018. meta-analysis
- [6]Chitosan supplementation and fat absorption in men and women.. J Am Diet Assoc, 2005. open-label
- [7]Randomized, double-blind trial of chitosan for body weight reduction.. Eur J Clin Nutr, 1999. RCT
- [8]Single-blind, placebo controlled randomised clinical study of chitosan for body weight reduction.. Nutr J, 2016. RCT
- [9]L-ascorbic acid addition to chitosan reduces body weight in overweight women.. Int J Vitam Nutr Res, 2014. RCT
- [10]Chitosan potentiation of warfarin effect.. Ann Pharmacother, 2007. observational
- [11]Safety of chitosan bandages in shellfish allergic patients.. Mil Med, 2011. observational
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract; the fecal-fat study is labelled as non-randomized. Industry ties: Healtheries of New Zealand support for one Cochrane-included trial run by the review authors (PubMed conflict statement); fungal-chitosan trial: two authors affiliated with the manufacturer KitoZyme despite a no-competing-interests statement (PubMed affiliations, PMC4706713), flagged by the independent reviewer and disclosed. Efficacy and safety framing from the NIH ODS weight-loss fact sheet (opened 2026-10-10, updated May 18, 2022). Two meta-analyses without a pooled n in their abstracts appear in insights only. Retraction, expression-of-concern and erratum check run on all 10 PMIDs: none flagged. Page set indexable.