This study try to identify differences in cost, length of operation and results between two different bariatric surgical techniques, the laparoscopic Roux-en-Y gastric bypass and the Single anastomosis laparoscopic gastric bypass. The study will be conducted in a Spanish public health system hospital.

The patients of the trial will have the preoperative studies, hospital treatment during the admission, postoperative treatment and follow up as any other patient included in the hospital bariatric surgery program. No new methods are applied other than randomly choose the surgical technique.

Patients will be randomized in a 1:1 ratio to each group.

One group of patients of the study will have done the simplified laparoscopic gastric bypass, with a vertical gastric pouch of about 20 ml, a 150 cm Roux-en-Y limb constructed in an antegastric antecolic fashion, and a biliary limb of 100 cm. Anastomosis will be done with endoscopic surgical linear stapler, closing the apertures with continuous absorbable running sutures. The Petersen space and the mesenteric defect will be closed with non-absorbable sutures.

The other group of patients will have performed the single anastomosis gastric bypass, also known as the Minigastric bypass (MGB), which have a vertical gastric pouch about 100-150 ml, and an end to side gastro-jejunal anastomosis at 200 cm from Treitz angle. The anastomosis will be done with endoscopic surgical linear stapler, closing the aperture with continuous absorbable running sutures.The Petersen space will be also close with non-absorbable sutures.

The investigators randomly assigned 10 patients to each group, n=20. Considering that one of the methods is basically the same than the other, but for the Roux-en-Y construction, it is expected a clear difference in operating room (OR) time, between groups. Fisher Test, will be used for the statistical analysis, assuming a risk of 0.05 and a statistical power of 90%, and Mann-Whitney test for quantitative parameters.

Once patients were included in the study, they were randomized in a 1:1 ratio to the conventional laparoscopic gastric bypass group or the single-anastomosis laparoscopic gastric bypass (Mini gastric bypass) group and were also blinded to the surgeon until surgery. The method of randomization was concealed envelopes.

Inclusion Criteria:

• criteria for bariatric surgery published in 1991 for the National Institutes of Health of the USA.
• age between 18-65 years-old.
• BMI between 40-50 kg/m2
• Obesity for more than 5 years of evolution
• Fail in medical supervised weight loss program
• patient knowing of the mechanism of weight loss after surgery and agreement to collaborate with medical recommendations, diet, medical treatment, as well as the visit established in the follow up program
• patient accepting that surgery objective is not to achieve the ideal weight.
• signed specific informed consent
• women will agree in avoid gestation during one year after surgery

Exclusion Criteria:

• Patients unable to sign the informed consent form because of a mental disorder.
• endocrine diseases causing obesity
• unstable mental disorder, evaluated for a psychiatry MD.
• high anesthetic risk making surgery too risky.
• Malignant neoplasm
• Gastroesophageal reflux disease (GERD) with endoscopic esophagitis

The plan is to publish the results of our study in a scientific journal when it be completed, not to publish the individual patient data, just the global data comparing both groups of study.