Chitosan is a sugar derived from the outer skeletons of shellfish, including crab, lobster, and shrimp. It is processed into over-the-counter dietary supplements widely marketed for weight loss. The promotion of these supplements centers on their potential to help with weight reduction.
The Proposed Mechanism of Action
The theory behind chitosan’s role in weight loss is based on its chemical properties. Chitosan is a polysaccharide that the human body cannot digest. In the stomach’s acidic environment, it develops a positive ionic charge that is thought to attract negatively charged molecules, such as dietary fats.
This attraction is often compared to a “fat magnet,” where chitosan binds with ingested fats before they can be absorbed. This binding action forms a large, indigestible mass of fat and chitosan that is too large for the intestines to absorb. Consequently, the bound fat is excreted from the body, which would, in principle, reduce the total number of calories absorbed from a meal.
Scientific Evidence and Clinical Findings
Initial investigations into chitosan’s effectiveness produced some promising, albeit modest, results. Early, smaller-scale studies suggested that supplementation could lead to a small amount of weight loss compared to a placebo, which helped fuel its popularity.
However, subsequent and more comprehensive research has tempered these early expectations. Large-scale systematic reviews and meta-analyses conclude that when only the most robust trials are considered, the effect of chitosan on body weight is minimal. The observed weight loss is not considered clinically significant, meaning it is unlikely to have a meaningful impact on a person’s health.
One meta-analysis found that while chitosan led to a statistically significant reduction in body weight, the average amount lost was less than one kilogram. The current body of high-quality scientific evidence does not substantiate the claims that chitosan is an effective tool for significant weight loss.
Safety Considerations and Side Effects
The primary safety concern with chitosan relates to its origin. Because it is derived from crustaceans, individuals with a known shellfish allergy must avoid it to prevent a potential allergic reaction. For individuals without allergies, the most commonly reported side effects are gastrointestinal. These can include:
- Gas
- Bloating
- Constipation
- Upset stomach or nausea
Because of its proposed fat-binding mechanism, there is a theoretical risk that chitosan could interfere with the absorption of certain nutrients and medications. Specifically, it may reduce the uptake of fat-soluble vitamins, which include vitamins A, D, E, and K. It is advisable to consult a healthcare provider before using chitosan, especially for those taking other medications or with pre-existing health conditions.