Supplement analysis backed by scientific evidence · PT

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Limited evidenceWeight management

Chitosan

Chitosan is sold as a "fat magnet", but the Cochrane review found no clear difference in faecal fat excretion — the exact measure the mechanism predicts. Pooled weight loss is around 1-1.7 kg, and shrinks further when the analysis is restricted to larger, longer, better-concealed trials.

What the science says

  • Weight loss is small and quality-dependent Limited evidence

    The Cochrane review of 15 trials (1,219 participants) found -1.7 kg versus placebo (95% CI -2.1 to -1.3), but analyses restricted to trials meeting allocation concealment criteria, or that were larger or longer, produced substantially smaller decreases. A later meta-analysis of 15 trials (1,130 subjects) found -0.89 kg (95% CI -1.41 to -0.38). The better the trial, the smaller the effect — a classic signature of bias rather than a real effect.

  • The fat-trapping mechanism is not confirmed in humans Limited evidence

    Cochrane found no clear difference between chitosan and control in faecal fat excretion. If chitosan bound meaningful amounts of dietary fat in the gut, that fat should show up in the stool. It does not, which undermines the marketing rationale.

  • Small reduction in total cholesterol Limited evidence

    Cochrane reported total cholesterol -0.2 mmol/L (95% CI -0.3 to -0.1) alongside small decreases in systolic and diastolic blood pressure. As with weight, these shrank in the higher-quality subset, and no trial has measured mortality or morbidity outcomes.

  • Body fat and BMI Limited evidence

    A 2020 meta-analysis found BMI -0.39 kg/m² and body fat -0.69 percentage points, with larger effects at doses above 2.4 g/day and in trials shorter than 12 weeks. Effects that appear only in short trials and fade with duration are not a good basis for long-term use.

Dosage & safety

Studied doseTrials typically used 1-3 g/day, most often 1 g three times daily immediately before or with meals, for 4-24 weeks. Doses above 2.4 g/day showed slightly larger effects in subgroup analysis, at the cost of more gastrointestinal complaints.
SafetyConstipation, flatulence, bloating and nausea are the usual complaints. Chitosan is derived from crustacean shells, so people with shellfish allergy should avoid it — the principal shellfish allergen is a muscle protein rather than shell chitin, but cross-contamination cannot be excluded and reactions have been reported. Because it binds lipids in the gut it may reduce absorption of fat-soluble vitamins A, D, E and K with prolonged use, and it can interfere with absorption of oral medications, so separate dosing by several hours. There are case reports of raised INR in patients taking warfarin. Avoid in pregnancy and breastfeeding.

Scientific references

Where to buy

NOW Foods, Chitosan, 240 Veg Capsules

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