(This story has been refiled to correct the affiliation of researcher in paragraph 3) By Kathryn Doyle (Reuters Health) – In a head-to-head comparison over 15 years, diet and exercise outperformed the drug metformin in preventing people at high risk for diabetes from developing the disease. Metformin, which helps control blood sugar and can be used alone or in combination with insulin to treat type 2 diabetes, also lowered the risk of developing the disorder in the study group, just not as much as making healthy lifestyle changes did. “The lifestyle intervention was more powerful in preventing or delaying diabetes development during the original three-year Diabetes Prevention Program and remains more powerful over the entire 15-year study,” said professor David M. Nathan of the Massachusetts General Hospital in Boston, a coauthor of the new paper.