Fat Metabolism in African Americans

Background: - Melanocortin receptors are proteins in the body that help send messages between body systems. One such receptor, the melanocortin 3 receptor (MC3R), is important for regulating body weight. Differences in MC3R can affect fat metabolism - or how the body handles fat. Some people who have changes in the MC3R genetic code are heavier than those who do not have these changes. These changes are found more often in African Americans. Researchers want to study the MC3R in African American adults to see how these changes may affect fat metabolism. They will look at overweight adults with either the most common genetic code for the MC3R or a rare variant. Objectives: - To study the role of the MC3R in body weight and fat metabolism. Eligibility: - Healthy African American volunteers between 18 and 55 years of age. - Volunteers must be overweight (body mass index at least 30 kg/m2) but weigh less than 450 lbs. Design: - The study consists of an outpatient screening visit and a 7-day inpatient visit with dietary studies. - Participants will be screened with a physical exam and medical history. Blood samples will be collected. (Participants will need to fast for 10 hours before giving blood samples.) A body scan will be given to determine fat, bone, and muscle content. Participants will complete a 3-day dietary assessment to record their food and drink consumption. They will also have an exercise test to look at heart and lung function. - Participants will have a 7-day inpatient stay. They will have a regular diet for the first 3 days of the study. For the final 4 days, they will have a diet with a higher fat content. - During the inpatient visit, participants will have the following study procedures: - Body measurements - Daily exercise routine - Imaging studies of the body - Measurement of a whole day s energy expenditure (spending one day in metabolic chamber-day 5) - Frequent blood samples - Urine collection for 24 hours (days 3 and 7) - Fat biopsy (collection of a small sample of fat tissue from under the skin on the abdomen) - Insulin and metabolism tests while eating the two different diets (day 4 and day 7). - After the final insulin and metabolism test, participants will be discharged from the study.