My research is devoted to advancing knowledge about prevention and treatment of type 2 diabetes, obesity, and their complications. My major research programs have been a 43-year longitudinal population study of type 2 diabetes and related conditions and two multi-center randomized clinical trials – the Diabetes Prevention Program (DPP) and Action for Health in Diabetes (Look AHEAD). This research has influenced how doctors and scientists define diabetes, classify its type, and identify factors that make some people more likely to develop type 2 diabetes. It has shown that diabetes in pregnant women affects not only their own health, but the health of their children for years to come. The DPP and Look AHEAD clinical trials study the health benefits of lifestyle changes (primarily weight loss) in persons who are at risk of getting type 2 diabetes or already have the disease. They showed that weight loss or the medicine metformin can help people prevent or delay getting diabetes, and that weight loss can improve several aspects of health in adults with type 2 diabetes.