Overweight and obesity are important risk factors for type 2 diabetes. The marked increase in the prevalence of overweight and obesity is presumably responsible for the recent increase in the prevalence of type 2 diabetes. Lifestyle modification aimed at reducing energy intake and increasing physical activity is the principal therapy for overweight and obese patients with type 2 diabetes. Even moderate weight loss in combination with increased activity can improve insulin sensitivity and glycemic control in patients with type 2 diabetes and prevent the development of type 2 diabetes in high-risk persons (ie, those with impaired glucose tolerance). The American Diabetes Association, the North American Association for the Study of Obesity, and the American Society for Clinical Nutrition have joined together to issue this statement on the use of lifestyle modification in the prevention and management of type 2 diabetes.