This study will compare the physiological effects of two isoenergetic, nutrient-controlled diets that differ in glycemic index. The diets will be studied in obese male adults in a 10-day crossover feeding trial. Hypothesis: Obese subjects will show improvements in clinical endpoints associated with risk for diabetes and cardiovascular disease (CVD) after consuming a controlled low (compared to high) glycemic index diet for 10 days. 1º endpoint: insulin sensitivity as measured by the modified Frequently Sampled Intravenous Glucose Tolerance Test (FSIVGTT). 2º endpoints: CVD risk factors; postprandial studies of oxidative stress; thermic effect of food.