Medically Reviewed by Melinda Ratini, MS, DO on April 28, 2023
2 min read

Chitosan is a type of fiber taken from the exoskeleton of insects and the shells of crustaceans such as:

  • Shrimp
  • Clams
  • Lobster

Some people take chitosan to try to lose weight. Chitosan is sold over the counter as a "fat blocker" or "fat trapper." The claim is that the supplement might reduce the amount of fat absorbed in your gastrointestinal tract. The FDA has warned about such claims. It says there is no reliable scientific evidence. A review of high-quality studies shows that overweight people who took chitosan did not lose significant amounts of weight.

Scientists have also looked at whether chitosan helps lower cholesterol levels. In some recent well-designed studies, chitosan reduced total cholesterol as well as LDL "bad" cholesterol. But other studies have shown conflicting results and more research is needed.

Early studies in people have hinted that varying forms of chitosan might also help:

Again, more research is needed to study chitosan for these conditions.

Optimal doses of chitosan have not been set for any condition. Quality and active ingredients in supplements may vary widely. This makes it hard to set a standard dose.

No. Chitosan is not found naturally in foods. It is extracted from a substance in shells of crustaceans.

Chitosan supplements appear to be safe when taken for a short time.

Side effects may include:

If you are allergic to shellfish, you should not take chitosan.

Chitosan may interfere with how blood thinners work in your body. If you take warfarin, talk to your doctor before taking this supplement.

It also might interfere with the way some antiviral agents work.

If you are taking medicine for diabetes, check with your doctor before taking chitosan and ask if there is anything you should watch out for.

Chitosan may also prevent your body from absorbing fat-soluble vitamins such as vitamins A, D, E, and K. Magnesium may also not be absorbed.

Always tell your doctor about any supplements you are taking, including natural ones and those bought without a prescription. That way, your doctor can check on any potential side effects or interactions with any medications.