Tantalizing promise, controversial results

by Allison Sarubin Fragakis, RD



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With low-carbohydrate diets still popular, supplements called carb blockers-such as Carb Trapper, Carb Cutter, and Carb-X-are suddenly everywhere. The claim: One or two tablets with a meal can block the absorption of about 400 calories' worth of bread, pasta, or potatoes.

But, do they really work? The main ingredients are bean and wheat germ extracts thought to stop carbohydrate absorption by inhibiting a digestive enzyme that breaks down starch. If starch passes through you undigested, you should lose weight.

That's the theory, but the truth is this: There's only a little evidence that they might work. In the '80s, several studies showed that the bean extract had no effect on calorie absorption or body weight.

But recently, however, researchers at the Mayo Clinic found that higher doses of bean extract (4,000 to 6,000 mg) and wheat germ extract (4,000 mg) slowed carbohydrate digestion. These higher doses are not available in commercial carb blockers, plus no one knows whether slowing carbohydrate digestion actually causes weight loss over time.