Chitosan is a carbohydrate, a polysaccharide obtained from the exoskeleton (the external skeleton) of crustaceans, in particular crab, shrimp and lobster. Chitosan can help reduce the absorption of cholesterol and fat in food. It is proposed against high cholesterol, obesity and Crohn’s disease and to treat complications of dialysis (including hypercholesterolemia). In the form of chewing gum it is instead proposed to prevent tooth decay.