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.

Inclusion Criteria:

• Men and women aged >18 years;
• Awaiting SG for the bariatric group or meeting the criteria for SG but not undergoing surgery for the non-surgical group.
• Menopause: defined as the absence of menses for a year and a serum follicular-stimulating hormone (FSH) >40 UI/L.
• Women taking oral contraceptive pills or hormone replacement therapy
• Patients with type 2 diabetes.

Exclusion Criteria:

• Type 1 diabetes;
• Disease (e.g., uncontrolled thyroid disease, Malabsorptive or overt inflammatory disorder)
• Metabolic bone disease other than osteoporosis or type 2 diabetes,
• Creatinine clearance <30 ml/min) or medication (e.g., glucocorticoids, anti-epileptic drugs, osteoporosis therapy, thiazolidinediones) affecting bone metabolism;
• Weight >204 kg (DXA weight limit) or BMI >60 kg/m2 (upper limit to allow for QCT examination);
• Current or planned pregnancy during follow-up; breast-feeding.

Gender role has been shown to influence lifestyle behaviours such as physical activity and nutrition. It is however unknown whether gender role influences adherence to the American Society for Metabolic and Bariatric Surgery physical activity and dietary intake/supplement recommendations that are important for bone/muscle health after bariatric surgery. A short questionnaire, the validated 12-item Bem Sex Role Inventory, will be administered to the participants to categorize them into 4 gender role categories. In an exploratory descriptive analysis, the investigators will calculate the proportion of participants in each gender role category meeting the dietary/supplement intake and physical activity recommendations and document the type and amount of physical activity they perform.

This is a multicentre, prospective and observational study comprising a SG bariatric group undergoing SG (n=117) comprising an equal number of men, premenopausal and postmenopausal women (n=39/group) meeting the inclusion/exclusion criteria, and assessed before, and at one and 3 years after SG. An obese non-surgical group (n=39; 13 men, premenopausal and postmenopausal women) meeting the criteria for SG but who will not undergo surgery during the 3-year period following recruitment will be assessed using the same tests and at the same timepoints.