Consenting, eligible patients previously enrolled in the ancillary study, "Longitudinal Assessment of Bariatric Surgery" (LABS), from Weill Cornell and the University of Pittsburgh will undergo the following measures: total body water by deuterium dilution (fat and fat-free mass (FFM)), extracellular water by sodium bromide tracer, body density by the BodPod, whole-body magnetic resonance imaging (MRI) (adipose tissue and its distribution; skeletal muscle mass; mass of liver, kidneys, heart, and brain), dual energy-X-ray absorptiometry (femur bone mineral density (BMD), total body fat, fat-free mass, and bone mineral content), and resting energy expenditure (REE). MRI will describe body composition changes at the tissue/organ level and adipose tissue distribution allowing us to address questions of biological and clinical importance including the body composition changes' influences on REE. The specific aims are to: 1) measure important components of weight change in patients who underwent bariatric surgery on measures of fat mass and its distribution and FFM (including bone mineral density, skeletal muscle, and specific organs) at T60 and T84 months following surgery, and also to compare compartment sizes with those seen in stable weight controls; 2) measure the amount of change in REE at T60 and T84 compared to T0, following weight loss induced by bariatric surgery and to determine its relation to changes in body composition compartments, and its duration over the follow-up period. Secondary research questions relate to changes in cardiac structure and function, physical activity associations with skeletal muscle changes, and adipose tissue depot changes as predictors of cardiometabolic parameters (glucose metabolism and serum lipid composition). Subjects will be women and men (n=100) equally distributed between the New York and Pittsburgh sites.