White Kidney Bean Extract

What the Experts Say
Starch blockers probably do allow complex carbohydrates to pass through the small intestine largely undigested, says Christine Gerbstadt, MD, RD, an American Dietetic Association spokeswoman.

“But when they get to the large intestine, the starches ferment, give off gas, and cause bloating and diarrhea,” Gerbstadt tells WebMD.

Gerbstadt says she doesn't recommend using starch blockers because there haven't been enough tests done in people showing that the products help.

Obesity expert Louis Aronne, MD, says his patients usually don't stick with starch blockers for long.

“We just don’t see people taking stuff like this on an ongoing basis. When patients come in taking a carb blocker, they end up stopping either because of the side effects or because of lack of effectiveness, or both,” says Aronne, who directs the Comprehensive Weight Control Program at New York-Presbyterian Hospital/Weill Cornell Medical Center.

MacKay stresses that it's important not to rely only on supplements for weight loss. As he puts it, those products "are not magic bullets," and a healthy diet and exercise are also needed for successful weight loss.

"If something sounds too good to be true, it probably is,” MacKay writes.