Diet-Induced-Obesity Resistant Phenotypes in Humans

Study Summary

Background: \- Obesity is the result of many factors, including genetics and lifestyle, such as over-eating high-calorie foods and not being physically active. Obesity affects approximately one third of adults in the United States. Researchers often study individuals who are already overweight and obese, but another approach is to examine people who stay thin despite eating whatever they want and not exercising. Studying these thin individuals will enhance understanding of why some people become obese and others do not, which may lead to novel treatments for obesity. Objective: \- To study the metabolism, body composition, body temperature, physical activity, and blood chemistries of healthy lean adults before and after adding 1,000 extra Calories per day to their normal diet. Eligibility: \- Healthy adults, 30 to 50 years of age, who have never been overweight after adolescence, who are currently weight-stable, sedentary, and eating without restrictions. Design: \- The entire study will take about 9 weeks and will include the following outpatient and inpatient visits: \<TAB\>- Outpatient screening visit and monitoring: Physical examination and blood test at screening; then, one week of physical activity monitoring (e.g., with a pedometer-like device called an accelerometer) and completing a food diary. \<TAB\>- Baseline inpatient visit (5 days): Volunteers will eat a normal diet to maintain body weight. Energy expenditure, body composition, physical fitness, activity level, and eating behavior will be measured. Urine and blood samples will be taken. Volunteers may go home for the weekend or stay at the metabolic clinical research unit (MCRU). \<TAB\>- Inpatient feeding week 1 (5 days): Volunteers will eat a normal diet plus milkshakes for added calories. All the same measurements during the baseline week visit will be repeated. \<TAB\>- Outpatient feeding weeks 2 3: Volunteers will eat breakfast at the MCRU everyday for the next 2 weeks and take prepared