Bariatric surgery is the most effective treatment to achieve type 2 Diabetes Mellitus (DM) remission in patients with severe obesity. However, there is little evidence of the effectiveness and pathophysiological mechanisms involved in metabolic improvement after hypoabsortive tecniques such as duodenal switch (DS), single anastomosis duodenal switch (SADI-S) or minigastric bypass (MGB). We have designed a randomized study to compare type 2 diabetes remission after the 3 bariatric procedures in patients with severe obesity (BMI > 45kg/m2) and to study the implication of gastrointestinal hormones, bile acids and gut microbiota in metabolic improvement in each procedure.

Patients fulfilling inclusion criteria will be randomly assigned 1:1:1 to undergo DS, SADI-S or MGB. Allocation of patients will be assigned by simple randomization with stratification according to baseline levels of HbA1c (greater or lower/ equal to 7 %).

Protocol 0. Screening visit: All participants will be required to sign the informed consent, according to the regulations of the Committee of the center. Clinical, analytical, and general physical examination data will be collected and it will be checked the fulfillment of inclusion criteria.

1. Visit 1 (1 week after screening visit): Anthropometrical data will be collected, and general biochemical analytics including HbA1c, lipid profile and nutritional parameters and vitamins will be performed. Also a standard meal test (SMT) will be done with determination of GLP-1, PYY, GIP , and ghrelin, insulin, glucose and succinate concentrations before and during the SMT. A complete body composition study including DEXA, BIA and cardiac resonance to determine epicardia fat will be performed. Feces samples will be collected to determine gut microbiota. Quality of live questionnaire will be provided.
2. Visit2 (1 month after surgery): Glycaemia diaries will be checked. Anthropometrical, general biochemical analysis with determination of HbA1c, lipid profile and nutritional parameters and vitamins will be done. SMT will be performed with determination of GLP-1, PYY, GIP, ghrelin, insulin, glucose. A determination of bile acids will be done before starting the meal test. feces samples will be collected to determine gut microbiota.
3. Visit 3 (3 months after surgery): Glycaemia diaries will be checked. Anthropometrical, general biochemical analysis with determination of HbA1c, lipid profile and nutritional parameters and vitamins will be done.
4. Visit 4 (12 months after surgery): The same determinations of visit 1 will be performed 12 months after surgery.

Inclusion Criteria:

• BMI>45 kg/m2
• T2D on treatment with hypoglycemic agents alone, insulin or both.

Exclusion Criteria:

• Type 1 diabetes
• Positivity for GAD auto-antibodies
• Secondary forms of diabetes
• Acute metabolic complications in the last 6 months
• Severe liver disease
• Renal dysfunction
• Patients under anticoagulant treatment
• Previous bariatric surgery
• Congenital or acquired abnormalities of the digestive tract
• Pregnancy
• Nursing or desired pregnancy in the 12 months following inclusion
• Corticoid use by oral or intravenous route for more than 14 consecutive days in the last three months.