Between 30 million and 50 million Americans are lactose intolerant, meaning they lack an enzyme needed to digest the main sugar in milk, and African-Americans, Asians, and American Indians are most likely to have the
condition. Ranging in severity from person to person, symptoms include cramping, bloating, gas, nausea, and diarrhea. These usually occur 30 minutes to two hours after one drinks or eats a dairy product.
Doctors can test for lactose intolerance using a breath test, which detects heightened levels of hydrogen; a blood test, before which the patient drinks a lactose-containing beverage; or a test of stool acidity (which undigested
lactose helps generate). There's also a cheaper, do-it-yourself approach to diagnosis, Bickston says. "Buy a tall container of milk, drink it, and call me the next day and tell me how the afternoon was," he says. If you experience
bloating, abdominal pain, or diarrhea, he says, you're probably lactose intolerant.
If so, don't despair. Over-the-counter pills can replace the missing enzyme, called lactase, and some milk and milk substitutes are lactose-free. Avoiding all dairy products, in any case, may not be necessary. Many lactase-deficient people "can tolerate small amounts of lactose," Bickston says.