Chronic Cold Exposure and Energy Metabolism in Humans

Background: \- Researchers are studying how metabolism and hormone levels change in response to mild changes in environmental temperature. Changes in metabolism may lessen with time because of hormonal adaptations. If this increase in metabolism continues for a longer period, mild cold exposure may cause weight loss. It is unclear whether exposure to a warmer temperature may cause opposite changes in metabolism. Researchers want to see if longer exposure (1 month) to different temperatures can affect how the body uses energy. Objectives: \- To test changes in energy metabolism in response to different room temperatures. Eligibility: \- Healthy men between 18 and 40 years of age. Design:

• The entire study will last for 4 months. It will involve a screening visit and a 4-month inpatient stay at the National Institutes of Health Clinical Center. The inpatient stay will be in a private room at the Metabolic Clinical Research unit. Study participants will be required to stay in the Metabolic Clinical Research unit during the night, but are free to leave during the day.
• At the screening visit, participants will have a physical exam and medical history. Blood samples will be collected. A heart function test and diet questionnaire will also be given.
• During the first month, the temperature of the private room will be set at to 75.2 degrees F. This will allow the body to become used to the testing environment.
• During the second month, the temperature will be set to either a cool (66.2 degrees F) or a warm (80.6 degrees F) temperature.
• During the third month, the temperature will return to 75.2 degrees F.
• During the fourth month, the temperature will be altered to the opposite temperature to the one set in the second month.
• Throughout stay, participants will have daily temperature monitoring and will keep a food diary. Once a week, they will collect all of their urine for 24 hours. Once a month, they will spend 24 hours in a metabolic suite to study their metabolism rate.
• Throughout stay, the food will be provided as part of the study.
• During the first and third month (75.2 degrees F) the participants will be allowed to leave the Metabolic Clinical Research unit during the weekends, while during the second and forth month (66.2 or 80.6 degrees F), the participants will be allowed to spend one weekend out of the Metabolic Clinical Research unit.
• Other tests, such as body scans, fat tissue samples, and imaging studies, will be performed as needed.