Chitosan is promoted as a fat "trapper," or blocker. It's a derivative of chitin, a fibrous substance that forms the cornerstone of shellfish exoskeletons. The initial claims for chitosan came from studies that showed it effectively mopped up fatlike industrial-waste products by forming an insoluble bond with them. That was followed by in vitro, or test-tube, studies, in which chitosan was placed in a beaker with a buffer and fat. The liquid was then stirred, and the resultant fat clumping was measured. Under those conditions, chitosan seemed to work.
But as with many other substances, what works outside the body isn't necessarily duplicated inside. Various studies that have tested the effects of chitosan on fat absorption and on weight loss in human subjects show that it has negligible effects. The latest research examining the fat-blocking characteristics of chitosan featured both male and female human subjects. 12 men and 12 women were told to follow specific diet plans that averaged five meals a day for 12 days. Participants took two capsules of a commercial chitosan supplement before each meal. The total daily doses averaged 2.5 grams. The extent of fat malabsorption induced by chitosan was measured by examining the subjects' fecal output.
The fat intake per dose of chitosan averaged 10 to 76 grams in the male subjects and 10 to 60 grams in the women. The 2.5 grams of chitosan per day increased the fecal excretion of fat by 1.8 grams a day in men and zero in women. Why the female subjects didn't get the effect wasn't clear, but the amount of fat excreted by the men was inconsequential. It would take more than seven months for them to lose one pound of fat due to chitosan.