Study volunteers will be admitted to the Clinical Research Center at Temple University Hospital. After an overnight fast, body composition will be determined non-invasively by bioimpedance analysis (4) and a 4 h euglycemic-hyperinsulinemic clamp (using only FDA-approved regular insulin) as previously described (5) will be performed during which serum samples will be obtained for measurement of glucose, insulin, free fatty acids, ketone bodies and lipids. Oxidative stress ( 6) will be measured by 24 hour urine collections (analyzed for isoprostene content (8-isoPGF 2α) throughout the study period. Respiratory gas exchange rates (7) will be determined at hourly intervals (with a metabolic cart (True One, Parvo Utah) during the clamp studies and once a day on Days 2 through 6. After that, (at about 1 PM on Day 1) the volunteers will be started on a diet program for 4 ½ days, consisting of 3 meals and 3 snacks over a 24 hour period and containing ~ 6000 Kcal/24 h. The main meals (containing ~ 1500 Kcal/meal) will be served at ~ 8AM (breakfast), 1PM (lunch) and ~ 7PM (dinner), the snacks (~ 500 Kcal/each) at ~ 11 AM, 4PM and 11PM. On days 5 and 6, volunteers will receive 3 meals, each will contain ~333 calories. Each morning blood samples will be obtained to measure glucose insulin, free fatty acids and ketone bodies. Daily 24 h urine collections will be obtained each day. In the morning of Days 5 and 7, all procedures described for Day 1 will be repeated. In the afternoon of Day 7, the volunteers will be discharged from the hospital.