Chitin ( N-acetyl-d-glucosamine) is a structural component of crustacean, fungi, insect, annelid, mollusk, and coelenterata exoskeletons. When deacetylated with a strong alkaline solution, chitin produces chitosan. Chitosan is typically insoluble in water, sucrose or NaCl solutions, ethanol, vegetable oils or propylene glycol, although the absence of acetyl groups allows solubility in aqueous solutions of organic acid. 

Efficacy

To date, a specific mode of antimicrobial action remains unclear, although in an anionic state, chitosan interacts with cell membranes and degree of deacetylation and depolymerization appear to influence level of activity. Gram-positive bacteria also appear to be less sensitive to chitosan than gram-negative types. A synergistic inhibition of yeast was also observed when chitosan was used in combination with benzoate. NaCl (2%) and proteins appear to antagonize activity; thus, the incorporation of chitosan in meat products is not appropriate. However, pure chitosan films reduced L. monocytogenes counts (2 log cycles) on inoculated bologna (10°C, 5 days).   

Why do people take chitosan

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.

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

Crohn's disease

Dental cavities

Anemia due to dialysis in people with kidney failure

Periodontitis

Those who have plastic surgery using donor tissue

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.