Chester J. Zelasko, Ph.D. | December 4, 2001

It seems you can't pick up a magazine or turn on the television without seeing an ad for a fat blocker. "Take these pills and you'll lose weight because they block fat!" Sounds too good to be true, doesn't it? You get to eat anything you want and all you have to do is take a few pills. What is this stuff? Does it work?

Almost every product available contains a form of chitosan. This is a type of fiber that's extracted from shellfish--people with shellfish allergies can't take it. Chitosan (pronounced KITE-o-san) can't be absorbed by the body--most types of fiber can't. Chitosan's claim to fame is that it will bind to fat molecules and prevent them from being absorbed, too. But it will also block the absorption of fat-soluble vitamins and beneficial omega-3 fatty acids. The chitosan-fat complex then passes through the body and is eliminated in the stool. The question is does chitosan work?

Most of the evidence is anecdotal--testimonials from people who have used the product. A Medline search found only a single study testing the efficacy of chitosan (1). The results were not encouraging--after 28 days, there were no differences in body weight between the placebo group and the group using chitosan. A single study doesn't mean that the product doesn't work. However, after being available for many years, it seems there should be several studies providing at least some support.

Why would someone lose weight taking chitosan? There may be a couple of explanations. First, at least one form of chitosan recommends that the product be taken 3-5 hours before bedtime with no food after that. Because most overweight people eat at least one-half their caloric intake after 5 p.m., the reduction in calories would explain most of the weight loss. Another chitosan product recommends that a person take the product 20 minutes before eating along with a full glass of water. That may also cause a person to eat less because the fiber and water would promote a feeling of satiety.

Does fiber block fat absorption? Yes, all types of fiber do to a limited degree. Eating five servings of fruits and vegetables every day will prevent the absorption of 75-150 calories from fat--and you'll be getting a whole lot more nutrition. It may not be as exciting, but it's tried and true.

If you really want to block the absorption of fat, do it the old-fashioned way: don't eat it.


  1. Pittler M, et. al. Randomized, double-blind trial of chitosan for body weight reduction Eur J Clin Nutr 53(5):379-81. 1999.
BBBOnLine Reliability Seal © 2011 Better Life Unlimited™
A division of Better Life Institute © (BLI, Inc.)
 Contact Us  |  Privacy Policy
SecurityMetrics Credit Card Safe