The central purpose of this project is to test whether AEE or change in AEE can be identified as a contributory mechanism to population-wide weight gain and, if so, to quantify its importance. In addition, we seek to understand the interrelationships between the adipocytokines and the hormones ghrelin and insulin as well as AEE in the regulation of body weight across the continuum of body mass indices (BMI) represented by these five populations.