The Diabetes Prevention Program is the first large study to show that losing weight and exercising can effectively delay diabetes in a wide range of overweight men and women who are just a step away from having full-blown diabetes. It gives doctors the first proven tools for countering the growing diabetes epidemic in the United States.

Participants were randomly assigned to different groups: a lifestyle group that received personal, intensive diet and exercise advice to reduce body weight by 7 percent; a group that took metformin, a drug approved for treating type 2 diabetes, and that was given information about the importance of weight loss and exercise; and a control group that took a placebo and also received general diet and exercise advice. (A fourth group took the drug troglitazone, until the Food and Drug Administration removed it from the market for safety concerns; that part of the study was stopped.)

The study found that the group that took the drug metformin also significantly reduced their risk of developing diabetes, although not as much as the lifestyle participants did. Those who took metformin - - marketed as Glucophage -- reduced their risk of diabetes by 31 percent. But unlike the outcome of lifestyle changes, the results show that metformin is not equally effective in reducing risk among different types of people. Metformin nearly matched lifestyle changes in reducing the risk of diabetes among participants who were ages 25 to 44. But it had no effect on the risk for men and women age 60 and older, nor for people with a body mass index (BMI) of 24 to 30. However, it matched lifestyle changes in reducing the risk for the heaviest participants, those with a BMI of 36 or higher. Overall, about 7 percent per year developed diabetes in the metformin group.