Shellfish can be a great addition to a weight loss diet — when they’re not smothered in melted butter. Shellfish are high in healthy fats such as omega-3 fatty acids and nutrients such as vitamin B12 and zinc.

But how healthy is the shell part of shellfish? While the shells themselves aren’t edible, chitosan is a supplement made from a substance found in the outer shells of crustaceans. It’s touted for its potential weight loss benefits.

In 2019, the global market for chitosan was valued at $6.8 billion, and it’s expected to grow almost 25% by 2027. Some supplement companies claim that chitosan can support weight loss and lower cholesterol levels (1).

But are these claims backed by scientific evidence? This article breaks down everything you need to know about chitosan supplements.

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Chitosan is derived from chitin, a fibrous compound found mainly on the hard outer skeletons of crustaceans and in the cell walls of some fungi. An enzymatic reaction produces chitosan — a more suitable form for supplements (2).

Chitosan is biodegradable and has been used in the development of antimicrobial films for food packaging. It’s also approved for use in wound dressings due to its ability to form a gel. Chitosan is now being studied for use in medications and tissue engineering (3, 4).

Most commercially available chitosan is derived from crabs and other shellfish (5).

Summary

Chitosan is a fibrous compound derived from the shells of crustaceans such as shrimp, lobsters, and crabs. It can be found as a dietary supplement, a component of food packaging, or an element of wound care.

Chitosan supplements are often touted as fat-blockers.

Chitosan is said to work by turning into a gel in the stomach. Some claim that when that gel moves from the stomach to the intestines, it binds to fat and cholesterol (2).

The idea is that chitosan may support weight loss and lower cholesterol by eliminating fat and cholesterol from the body instead of allowing the body to absorb them (2).

That’s why the labels on chitosan supplements direct consumers to take it just before meals. Otherwise, there would be nothing in the gut for it to bind to.

However, current evidence doesn’t support these claims.

Clinical trials in the early 2000s found that chitosan did not significantly increase fat excretion in stool. Although chitosan is a fiber and could very well form a gel in the body, there’s no indication that it actually traps fat (6, 7).

Summary

Some marketing claims state that chitosan supplements prevent the body from actually absorbing fat by trapping it in stool. However, there is no scientific evidence that chitosan increases fat loss.

Chitosan supplementation may benefit weight loss efforts and cholesterol reduction, although many of the studies supporting those claims are considered low quality. Chitosan’s effects on weight loss in particular are minimal, if they occur at all.

Weight loss

In a 2018 review, researchers analyzed data from 14 studies including a total of 1,101 participants with overweight or obesity. They compared weight loss outcomes in people taking chitosan supplements with those of people taking a placebo (2).

Results showed that chitosan supplementation slightly reduced body weight and body mass index (BMI) when paired with a calorie-restricted diet and physical activity (2).

These results support the findings of a similar, older review, which found that chitosan supplements may be more effective than a placebo as part of a short-term treatment plan for overweight and obesity (2, 8).

Both reviews noted improvements in cholesterol levels and blood pressure (2, 8).

However, the researchers reported that many studies on chitosan supplements were of poor quality and that there was significant variability among results. The studies that were deemed high quality found chitosan’s impact on body weight to be minimal (2, 8).

A small 2014 clinical trial found that supplementing with 3 grams of chitosan per day may be more effective for weight loss when paired with 2 grams of L-ascorbic acid — a type of vitamin C (9).

Summary

There is not consistent scientific evidence supporting chitosan use for weight loss. Chitosan supplements’ effect on body weight is likely clinically insignificant.

Reduced cholesterol levels

Chitosan may have a greater impact on cholesterol levels than on weight loss. A 2018 review that pooled data on cholesterol levels from more than 1,000 people concluded that supplementing with chitosan lowered both total cholesterol and LDL (bad) cholesterol (10).

Although HDL (good) cholesterol was unaffected, chitosan supplementation may still be an effective part of a cholesterol management plan (10).

However, there are other natural cholesterol reducers that have more evidence supporting their effectiveness than chitosan.

Summary

Studies show that chitosan may be somewhat effective at lowering cholesterol levels. However, more research is needed, and many other natural cholesterol reducers are backed by more evidence.

Side effects of chitosan supplements may include constipation, nausea, and an upset stomach (11, 12).

If you’re allergic to shellfish or mushrooms, you should avoid chitosan supplements.

Chitosan may also interfere with the absorption of fat-soluble vitamins such as vitamins A, D, E, and K, as well as calcium and magnesium. Therefore, chitosan supplement labels may encourage you not to take chitosan supplements at the same time as any other supplements.

Talk with a healthcare professional before taking chitosan if you’re taking any medications, including blood thinners. Chitosan may have a negative interaction with medications like warfarin (13).

Summary

Avoid chitosan supplements if you have an allergy to shellfish, and talk with a healthcare professional about potential medication interactions before supplementing.

The European Food Safety Authority’s Panel on Dietetic Products, Nutrition, and Allergies set the maximum recommended daily intake of chitosan at 3 grams. There is currently no recommended maximum amount established in the United States (2).

While studies have shown chitosan supplementation to be generally safe in adults, the doses studied range widely, from 0.34–3.4 grams of chitosan per day.

Therefore, there’s no consensus on the most effective dose for chitosan. But staying below that 3-gram maximum set by European safety authorities may be a good reference (2).

Check the supplement label to see how much chitosan is in one serving (remember that one serving may include multiple capsules) and how many servings are recommended per day. Add everything up to see the total daily dose.

When looking for a supplement, always verify that it has been third-party tested. Third-party testing ensures that the supplement meets certain purity and potency standards.

Look for a seal on the packaging from an organization such as NSF International, USP, or ConsumerLab. These seals are typically good indicators of supplement quality.

Summary

Talk with a healthcare professional before taking a chitosan supplement. If weight loss is your goal, they may be able to provide more personalized recommendations that are better suited for that purpose.

Chitosan is a widely available supplement promoted for weight loss. While some research indicates that it may be somewhat effective in conjunction with a calorie-restricted diet and exercise, more research is needed (2, 8).

Always proceed with caution when starting a new supplement regimen, and ensure that the benefits outweigh the potential risks. Where chitosan is concerned, its benefits for weight loss are inconclusive.