These are dietary supplements, once called starch blockers, that supposedly inhibit the metabolism of carbohydrates into glucose and fat, essentially "blocking" them from being absorbed.

Carb Blockers work by inhibiting the metabolism of carbohydrates into stored fat.

The critical ingredient of these products is called phaselous vulgaris, an extract from the northern white kidney bean. The extract interferes with an enzyme in the body called alpha-amylase that breaks down carbohydrates into glucose. Instead of carbohydrates being broken down and turning to fat, the carbs are excreted from the body before they can enter the bloodstream.