Q: I'm taking the fat-blocking drug Xenical. Is it a problem if I combine it with a carb-blocking supplement?
— Nancee Samloff
Glen Allen, Virginia

A: I don't have major concerns about Xenical, a lower dose of which was recently approved by the FDA for over-the-counter sales under the name Alli. However, I don't put much stock in it, either. The drug, which prevents enzymes in the intestine from breaking down fat molecules, does not work very well for weight loss. In studies, subjects who took Xenical for a year lost only about 13 pounds on average compared with a diet-only group that lost six pounds.

If you don't eat much fat, there won't be much in your intestine to block, so you gain little by taking Xenical. And if you eat a lot of fat, the drug can cause unpleasant side effects such as bloating and diarrhea. The drug can also reduce absorption of fat-soluble vitamins—A, D, E, and K—so you should take a multivitamin as a precaution.

As for the carbohydrate blocker, the evidence that such products work is slim. The supplements often contain an extract (phaseolamin) derived from white kidney beans that interferes with starch-digesting enzymes in the intestine. Usually your gastric system has a lot more enzymes than one pill can block; also, the blockers can cause the same kind of bloating and discomfort that some people get from eating beans.

If you want to control your intake of carbohydrates, the best way is to eat fewer of them and to replace simple carbohydrates (such as refined sugar or white flour) with quality ones that also deliver fiber—beans, apples, berries, and oats in particular. Soluble fiber slows the rise in blood sugar and insulin after a meal, so you're less hungry. I much prefer the idea of eating beans to the use of supplements based on beans.

And here's a thought about combining Xenical and a carbohydrate blocker: You are interfering with the absorption of two of the three macronutrients—protein is the third—that we need to survive. This essentially undermines the point of eating. Instead, why not choose nutritious food in sensible portions and save yourself a lot of money?

As a reminder, always consult your doctor for medical advice and treatment before starting any program.


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