A critical look at chitosan for weight reduction

Chitosan is a pulverized powder made from the shells of shrimp and crab. It was discovered as part of an effort to clean up oil spills.

Its value in blocking fat absorption in humans is controversial. Here are the results from relevant studies.

Most negative results come from research conducted at the University of California at Davis by Dr. Judith Stern, Distinguished Professor of Nutrition & Internal Medicine in the Department of Nutrition. In 3 studies, weight loss was not measured, but there was no evidence that chitosan blocked fat absorption from the intestines or fat excretion in the feces.

  • 2002: Chitosan supplements failed to increase fecal fat content and therefore did not block fat absorption.
  • 2003: Chitosan’s effect on fat absorption was statistically significant compared to placebo but clinically negligible.
  • 2005: For men, it would take more than 7 months to lose 1 pound of body fat.
    For women, no fat was trapped.

In contrast to these negative findings…


  • 29 healthy adults showed significantly increased fat excretion as measured in fecal samples.
  • No changes were seen with placebo.

In 2 clinical studies designed to measure weight loss?


  • 50 obese women (BMI greater than 30) participated in a 6-month program.
  • 2-hour group meetings with a physician, psychologist, and dietitian every 2 weeks.
  • Low calorie diet (1000 kcal/day), physical activity, and behavior modification were recommended.
  • Women who also took chitosan had significantly higher body weight loss (16 kg; 35 lbs) compared to the placebo group (11 kg; 24 lbs).
  • Wow!


  • 150 overweight adults followed the diet of their choice.
  • In addition, they received chitosan, placebo, or nothing.
  • Small but statistically significant differences were achieved in weight lose with chitosan (-2.8 lbs) vs placebo (-0.6 lbs) vs just diet (+0.8 lbs).

The bottom line?
Most study results dispute the claim that chitosan is a “fat blocker.” More importantly, the best results occurred when chitosan was combined with support from other dieters and healthcare professionals. When added to diet in the absence of this support, the results were disappointing.

3/3/07 13:58 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.