The prevalence of obesity has risen dramatically among children in the U.S. since the 1960s. Effective treatment of childhood obesity is widely recognized as instrumental to public health efforts to combat type 2 diabetes and heart disease. Evidence from animal studies, short-term human studies and epidemiology suggests that diets designed to minimize the rise in postprandial blood glucose, that is low glycemic index, may be useful in the treatment of obesity and related complications. This project proposes an month RCT comparing a low glycemic load diet to a conventional low fat diet. Both diet groups will receive identical treatment intensity, behavioral modification and physical activity recommendations. The primary endpoint will be change in percent body fat by dexa-scan at 18 months; other outcomes include insulin resistance and CVD risk factors. Compliance will be assessed by interviewer-administered, 24-hour dietary recalls.