Effect of Isocaloric Ultra Processed Versus Unprocessed Diets on Insulin Sensitivity

Background: Increases in obesity, diabetes, and some metabolic disorders may be linked to how much processed foods people eat. Researchers want to learn more about how processed foods affect metabolic health. Objective: To learn about how a processed versus unprocessed diet affects the body. Eligibility: Men ages 18-50 with stable weight and risk factors for diabetes Design: Participants will be screened over 3 visits. Screening includes: * Medical history and physical exam * Heart and blood tests * Psychiatric questions * Questions about eating, sleeping, and economic status * Riding a stationary bike * Trying a sample meal Between screenings, participants will eat prepared meals. They will wear an accelerometer to measure physical activity. They will write down what foods they eat and monitor their weight. Participants will have two 4-week stays in the clinic. They will: * Eat a special diet * Have activity and weight monitored * Drink water and collect urine samples to measure how many calories they are burning * Have resting energy expenditure measured with a clear hood over the head * Have a scan to measure body fat and bone density using low-dose x-rays * Have a scan on a table that slides into a metal cylinder in a strong magnetic field. They will get earplugs for the loud noises. * Have an ultrasound test to measure blood vessels * Have insulin and glucose infused into an arm vein. Blood will be taken over 10 hours through a plastic tube in the wrist. This will happen 4 times. * Spend multiple 24-hour periods in a room that measures oxygen used and carbon dioxide produced. * Give blood, urine and stool samples * Answer questionnaires and do computer tasks