Results are inconsistent and further studies are needed to better understand the impact of bariatric surgery on the bone-BMA relationship depending on the type of bariatric surgery: RYGB vs. SG. Future studies are also needed to define the molecular mediators of bone loss and BMA changes. Several molecular mediators have been considered including gut hormones, adipokines, gonadal hormones and more recently G-CSF. However, the evidence to support any of these alone or in combination as primary mechanisms of bone loss is scant.

The study will be to explore potential changes in BMA after bariatric surgery and search for possible associated factors. Specifically, we want to investigate if such changes in BMFF differed in participants among different surgical types (RYGB vs. SG) and diabetic status. Secondly, we want to explore factors associated with BMFF changes including metabolic homeostasis (glycemic control and blood lipid levels), adipokines (leptin and adiponectin), calciotropic hormones (Ca++, PTH…), body composition parameters and bone markers (cross-laps, P1NP and sclerostin). We hypothesize that the BMFF would particularly decrease after RYGB compared to SG and that participants with T2D would have a larger decrease in BMFF than participants without T2D.

Inclusion Criteria:

Postmenopausal women (defined as last menses >12 months)

• Obesity with a BMI ≥ 35 kg/m²,
• Patients with an indication for bariatric surgery with two surgical techniques, RYGB and SG, but who have never had a bariatric surgery procedure previously,
• Patients who have signed the informed consent.

Exclusion Criteria:

• History of an osteoporotic fracture 2- Current corticosteroid therapy or corticosteroid therapy within the past 3 months, C-onditions or treatments affecting bone metabolism (breast cancer treated with aromatase inhibitors, malabsorption, stomach cancer, primary hyperparathyroidism, uncontrolled hyperthyroidism…),
• History of radiation therapy to the lumbar spine or the hip being studied,
• Patients on hormone replacement therapy (HRT) or patients already on anti-osteoporotic treatment (bisphosphonates, strontium ranelate, teriparatide, or denosumab) other than calcium and/or vitamin D supplementation,
• Chronic kidney disease with a creatinine clearance (CKD-EPI formula) ≤ 30 mL/min,
• Weight > 160 kg, as the bone densitometer table is limited to this weight for the examination,
• Patients who have previously undergone bariatric surgery,
• Patients with orthopedic implants in both hips or the lumbar spine,
• Individuals unable to give personal consent,
• Individuals under legal guardianship or conservatorship,
• Patients not enrolled in a social security program.
• Any contraindication to MRI: (claustrophobia, patients with a pacemaker/defibrillator, cochlear implant, neurostimulator, or orthopedic implants in the hip, pelvis, or lumbar spine, etc.).

Sample population will be 40 postmenopausal women suffering from obesity, candidates for their first bariatric surgery procedure