What is chitosan and does it help with weight loss?

Chitosan is a fiber compound made from multiple saccharides or sugar molecules.  Therefore, it is actually a polymer of sugar or polysaccharide.  It is made by treating the chitin shell of crustaceans such as shrimp with an alkaline.  This process softens the shell and allows the polysaccharide to be put into pill form and be used a medicine.  

Chitosan is used as a supplement to treat obesity, elevated cholesterol, and Crohn’s disease. I would recommend that you discuss usage with a medical provider to ensure you do not have any contraindications and make sure it will not interact with your medications.  Although it might be used for other conditions, I am going to focus on weight loss and fat absorption.  

Chitosan appears to be safe for most people when taken by mouth for up to six months. The biggest side effect would be an allergic reaction so I would not take it if you are allergic to iodine or shellfish which should be obvious since it is chitosan is made from the exoskeleton of shellfish.  Besides allergies, the most common side effect is mild stomach upset, constipation, or gas and it is clear why it would do this since it is both a form of fiber and tends to hold fats in the bowel for bacteria to digest.  Chitosan can also reduce the absorption of medications and vitamins.  

Weight Loss Research:  There is plenty of research on chitosan and weight loss.  There is conflicting evidence about the effectiveness of chitosan for weight loss, but there is plenty of evidence that it binds cholesterol and fat molecules in the GI tract. Research suggests that combining chitosan with a calorie-restricted diet might result in a small amount of weight loss. But taking chitosan, without cutting calories, doesn’t seem to cause weight loss.   

Many studies on chitosan have design flaws that make their results questionable​[1]​.  Yet others were paid for by supplement companies which indicates bias.  One such study looks at fat and cholesterol absorption with and without chitosan.  With the use of chitosan, one gram of chitosan reduced absorption of peanut oil by 2-8 grams a day and cholesterol by 50-65 mg.  It is a small change, but it could make a difference.  

Chitosan has been sold in tablet form as a fat binder. A Cochrane meta-analysis review looked at this supplement and found that only poor-quality studies who’d any significant change in body fat absorption.   In these studies, the data only indicated a minor effect on body weight. Other higher quality trials were done, but they showed no significant effect of chitosan and no clinical justification for advising overweight patients to take chitosan supplements​[2]​.  A similar finding was reported in the American Journal of Clinical Nutrition​[3]​.  

The bottom line: Chitosan does not work.  It is not a good source of fiber and ti does not appear to affect fat absorption significantly.  If you took it for one year, you might lose 2 pounds of fat.  There are better means for weight loss.