Study of the Effect of a Very-Low-Carbohydrate Diet on Energy Expenditure

Study Summary

Background: \- Popular weight loss plans often restrict carbohydrates or fat. Research shows that very-low-carbohydrate (ketogenic) diets lead to greater weight loss than low-fat diets. Researchers want to know if eating fewer carbohydrates changes the number of calories the body uses. They also want to know how a ketogenic diet affects hunger, hormones, and food preferences. Objectives: \- To better understand how the body responds to different diets. Eligibility: \- Men 18 to 50 years old who are healthy but overweight. Design: * Participants will have 3 screening visits: 1. Medical history, physical exam, blood test, and EKG. They will eat during the visit. 2. For the week before the visit, participants will wear physical activity monitors daily. They will record everything they eat and sample the special diet. At the visit, they will receive an EKG and heart rate test while biking for 30 minutes. 3. For the week before the visit, participants will wear the physical activity monitors. They will eat all their meals from the special diet that will be provided. At the visit, they will answer questions and bike for 60 minutes. * After screening, for 1 week, participants will visit the clinic daily to receive that day s food. They will not eat or drink anything else except water. * Then participants will stay at the clinic for 8 weeks. They cannot leave but can have visitors. Participants will wear physical activity monitors, bike daily, and follow different diets. Tests will be given daily, and may include weighing, X-rays, and blood and urine tests. They will spend several days in a monitored room to test oxygen and carbon dioxide.