This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To investigate comparative medium- and long-term effects and safety, and to obtain a clinically meaningful ranking of different metabolic bariatric surgery procedures (adjustable gastric banding, sleeve gastrectomy, Roux-en-Y gastric bypass, one-anastomosis gastric bypass, gastric plication, biliopancreatic diversion with duodenal switch, and their variations) compared to each other and to non-surgical treatment (e.g. usual care with intensive lifestyle interventions or pharmacotherapy) on outcomes relevant to adults with obesity and type 2 diabetes, by considering both randomised controlled trials and cohort studies.