Derived from the exoskeleton of crustaceans such as crabs, crayfish, and shrimp, chitosan is a dietary fiber that contains no calories and possesses many of the same properties as fiber. However, unlike plant fiber, it has the ability to significantly bind fat, acting like a "fat sponge" in the digestive tract.
According to PDR Health, chitosan is a supplement people take to lose weight. The fat binds to the Chitosan fiber and becomes a large mass, which the body cannot absorb. The supplement also claims to help cleanse the digestive tract of waste that may cause bloating because chitosan moves through the digestive tract undigested.
Chitosan can absorb up to 4-6 times its weight in fat. This means that for every gram of chitosan that you consume as a supplement, you'll prevent the absorption of about 4-6 grams of fat!