Background: Bariatric surgery is gaining in popularity. While it's health benefits are undisputed, the older malabsorptive bariatric procedures (Roux-in-Y gastric bypass - RYGB and biliopancreatic diversion - BPD) are associated with an increased risk of fractures and falls as early as 3-5 years after surgery. Sleeve gastrectomy - SG is now the most performed bariatric procedure. Although SG does not cause malabsorption, it is predicted to result in bone and muscle loss via weight loss and weight loss-independent mechanisms. Primary aim: to compare the changes in spine volumetric bone mineral density (vBMD) by quantitative computed tomography (QCT) and muscle mass at mid-femur by computed tomography (CT) at 3 years in the 3 groups of: 1) men; 2) premenopausal women; 3) postmenopausal women after SG versus their respective non-surgical peers who did not undergo SG in the 3-year period following recruitment. Secondary aims: to compare the changes in vBMD by QCT at skeletal sites other than the spine and in areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA), whole-body muscle mass by DXA, muscle quality by CT at mid-femur and muscle strength as well as in selected physical performance and capacity tests shown to predict falls and fractures between 0-1 and 1-3 years after SG in the same 3 groups after SG vs. in the respective non-surgical groups.