Subjects will complete an initial eucaloric feeding study day. During this study day, subjects will receive 100% of their calorie requirements. 24-hour energy expenditure will be measured.

Following the eucaloric feeding study day, subjects will undergo the underfeeding and overfeeding arms in random order. During the underfeeding study arm, subjects will receive 50% of their calorie requirements (as determined during the initial eucaloric study day) for 3 days. 24-hour energy expenditure will be measured.

Following the eucaloric feeding study day, subjects will undergo the underfeeding and overfeeding arms in random order. During the overfeeding study arm, subjects will receive 150% of their calorie requirements (as determined during the initial eucaloric study day) for 3 days. 24-hour energy expenditure will be measured.

To assess 24-hour energy expenditure and substrate utilization subjects will spend 23 hours and 15 minutes each day in the metabolic chamber at the UNC NRI. Subjects will be requested to arrive at the study center each morning following a 10hour overnight fast. During each study day, subjects remained sedentary. All meals were provided and were tailored to each subject's specific energy requirements and the study protocol (i.e. 50% or 150% of calorie requirements).

24-hour energy expenditure will be assessed using the metabolic chamber at UNC NRI. Energy expenditure will be measured during eucaloric feeding (subjects will receive 100% of calorie requirements), as well as during 24, 48 and 72 hours of under and overfeeding.

RNA will be extracted from whole blood. Transcriptomic profile will be assessed by microarray