We've got a message for the 20 million Americans with diabetes: Pick up a dumbbell. For years, doctors have recommended cardio to help control blood-sugar (glucose) levels, but now research shows that strength training enhances the effect. In a study published in the Annals of Internal Medicine, adults with type 2 diabetes did either a cardio workout, a resistance training session, or both three times a week. After five months, the group that did the combo routine had lowered their glucose levels by nearly twice as much as the other exercisers. "Aerobic and resistance exercise work in complementary ways to improve the way your body processes glucose," says study author Ronald Sigal, M.D., an associate professor of medicine and kinesiology at the University of Calgary. "If people with diabetes can keep their blood sugar close to normal, they'll be less likely to get heart or kidney disease, have a stroke, or develop blindness." So consider this advice doctor's orders: Do three strength training workouts and five 30-minute (or longer) cardio sessions every week.