Extending Time Without Diabetes After Bariatric Surgery: a Trial Comparing the Metformin Addition or Not to Standard Care

Inclusion Criteria: * Adults 18-70 years old * Having undergone gastric bypass or sleeve gastrectomy 12 to 36 +/-3 months before inclusion * "ex-T2D" treated with at least one anti-diabetic drug before bariatric surgery or HbA1c ≥ 6.5 % before bariatric surgery * HbA1C \< 6.5 % at inclusion with no anti-hyperglycemic medications for the last three months * Written consent Exclusion Criteria: * Known type 1 diabetes * Pregnancy and breastfeeding * Estimated glomerular filtration rate\<44 ml/min (MDRD) * Known intolerance to metformin * Known contraindication to metformin: * Acute metabolic acidosis * Acute affection which could lead to renal deterioration (ex: dehydration, serious infection, shock, intravascular administration of iodinated contrast agent within the last 48 hours) * Acute or chronic disease which could lead to a tissue hypoxia (ex : severe cardiac insufficiency, severe respiratory insufficiency, myocardial infarction within the last 3 months, shock) * Hepatocellular insufficiency * Prothrombin ratio ≤ 50% * SGOT or SGPT levels ≥ 10 times the upper limits of the normal range * Alcohol use disorder * Medications and medical conditions likely to confound the assessment of diabetes: * glucocorticoids treatment * renal graft * Cushing's syndrome * acromegaly * fasting plasma triglyceride \> 600 mg/dl despite treatment * Patient under legal protection