Alli prevents your body from digesting about 25 percent of the fat in your food. In studies, people who took the pill while dieting typically lost 50 percent more weight than those who just dieted. But after six months, people on Alli had lost an average of only 5 percent of their body weight—about ten pounds; the diet-only group lost about seven pounds, on average.
Experts stress that Alli must be taken while following a reduced-calorie, low-fat diet (no more than 30 percent of calories from fat). "Eating too much fat will produce undesirable side effects," says James W. Anderson, MD, professor of medicine and clinical nutrition at the University of Kentucky. Those side effects can include diarrhea, gas with oily discharge, and incontinence.
This is why some think the drug will provide a kind of Pavlovian conditioning. "The effects of this drug reinforce a healthy lifestyle," says Jennifer Lovejoy, PhD, dean of the school of nutrition and exercise science at Bastyr University in Kenmore, Washington. "You quickly learn where there are hidden sources of fat."
Not all obesity researchers are charmed. "The total weight loss isn't much to get excited about, and the price to the consumer can get pretty high," says Kelly Brownell, PhD, director of the Rudd Center for Food Policy and Obesity at Yale University. Alli costs $1 to $2 a day, which means a 180-pound woman will pay up to $360 to lose just nine pounds over six months. If she follows the same diet and doesn't take Alli, she'll lose six pounds, no charge.
Alli is considered safe for long-term use. The FDA recommends that people with diabetes or thyroid disease or those on blood thinners consult a physician before taking it; because Alli could cause the loss of fat-soluble vitamins (A, D, E, K), users are advised to take a multivitamin at bedtime.