The purpose of this study is to assess the safety and efficiency of OAGB compared to RYGB

Rationale: to compare two different types of gastric bypass operations on surgical outcome.

Objective: to compare two established procedures in order to find the optimal procedure in terms of weight loss and metabolic control that is associated with the fewest side-effects and complications, and decreased invasiveness.

Study design: A multicentre, open label, non-inferiority randomized controlled trial Study population: Patients are eligible for inclusion if their body-mass index (BMI) was 40 kg/m2 or higher, or 35 kg/m2 or higher with the presence of at least one comorbidity (type 2 diabetes, high blood pressure, obstructive sleep apnoea, dyslipidaemia, osteoarthritis of the hip or knee) and a positive evaluation by our bariatric multidisciplinary team (BMDT) and are aged 18-65.

Intervention: Group 1: One Anastomosis Gastric Bypass with 150cm biliopancreatic limb. Group 2: Roux-en-Y gastric bypass with biliopancreatic limb of 150cm and 75cm alimentary limb.

Main study parameters/endpoints:

Primary endpoint:

% Excess BMI loss at two years

Secondary endpoints:

Metabolic status Nutritional status Comorbidity remission QOL Complications or serious adverse events (SAE's)

Inclusion Criteria:

• body-mass index (BMI) of 40 kg/m2 or higher, or 35 kg/m2 or higher with the presence of at least one comorbidity (type 2 diabetes, high blood pressure, obstructive sleep apnoea, dyslipidaemia, osteoarthritis of the hip or knee)
• a positive evaluation by our BMDT

Exclusion Criteria:

• Presence of H. Pylori, resistant to eradication therapy
• chronic diarrhoea
• history of previous bariatric or extensive abdominal surgery