This is adapted from the book, Eat Smart, Play Hard, by RW USA Nutrition Editor Liz Applegate.
Made from chitosan, a type of fiber from shrimp and crab shells, these supplements claim to stop your intestines from absorbing fat, which should lower the number of calories that enter your body. The theory is that chitosans large, bulky chemical structure acts much like a sticky piece of Velcro that traps small amounts of fatty substances in your intestines. The chitosan, along with the fat and cholesterol, doesnt get absorbed by your intestines; instead, it all ends up in your stool. As a result, calories get sucked out of your body before they can be absorbed.
That all sounds great until you stop and think about it. If weight loss were really that easy, everyone would be as skinny as a supermodel. The fact is that its not that easy.
Over several weeks, researchers fed laboratory mice a high-fat diet that was 10 to 15 percent chitosan by weight. The animals gained significantly less fat than control mice eating the same fat-laden diet. This may sound promising, but the mice ate large amounts of chitosan (much more than the recommended amount on many product labels), which resulted in large amounts of fat being excreted in their feces. In humans, this condition of excessive fat in the stool is called steatorrhea, which is not only uncomfortable but also embarrassing.
Studies done on people are few and far between, and the results are less promising than those done on mice. One study concluded that chitosan doesnt work for people, period. Other research shows that chitosan may be able to bind 3 to 4 grams of fat per meal at most. That amounts to a mere 30 calories half the amount in a banana. Thats hardly a situation where you can eat anything you want and still lose weight.
Chitosan may be more promising for your heart health, however. While the men in one study didnt lose weight, their blood cholesterol levels fell significantly. Levels of the good HDL cholesterol rose, which suggests that chitosan may have the potential to lower cholesterol. But it may also lower your absorption of fat-soluble vitamins (such as vitamin E) and cause intestinal yeast overgrowth.
Besides chitosan, there are many brands of fat blockers on the market. The packaging for these generally proclaim that the products "block fat absorption."
My recommendation: Fat-blocker pills cost about $10 for a 1-week supply, so spend your money on something more worthwhile.