Participants who are assigned to the diet plus exercise group will also attend a supervised exercise session three times a week for 6 months. Each session will last 1 to 1 ½ hours and will include aerobic exercise and weight training. Participants who have diabetes or who are receiving medication to control their blood sugar will have their blood sugar measured before and after exercising, based on study staff recommendations. At the end of Month 6, all participants will attend a study visit for repeat baseline testing.