This study try to identify differences in length of operation, weight loss and complications, between two different bariatric surgical techniques, the laparoscopic Roux-en-Y gastric bypass and the laparoscopic Roux-en-Y banded 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. The study cases will have placed around the gastric pouch a band of polypropylene mesh, and will be randomly choose between the participants.

Patients will be randomized in a 5/3 (study/control) ratio.

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 laparoscopic Roux-en-Y banded gastric bypass. This technique is identical to the one performed in the other group, but differs in that a polypropylene mesh (10x65 mm) is placed 15 mm proximal to the anastomosis around the gastric pouch, and the gastric pouch is about 15 mm longer.

The investigators randomly assigned 50 patients to the study group (Laparoscopic Roux-en-Y banded gastric bypass) and 30 to the control group (Laparoscopic Roux-en-Y gastric bypass) , n=80, and were also blinded to the surgeon until surgery.

One of the methods is basically the same than the other, but for the placement of the polypropylene mesh around the gastric pouch above the anastomosis, and patient series with Laparoscopic Roux-en-Y banded gastric bypass showed long term better weight loss than other series with not banded gastric bypass, thus it is expected a difference in long term weight loss between groups.

Fisher Test will be used for the statistical analysis, assuming a risk of 0.05 and a statistical power of 90%.

Sample size is calculated considering bibliographic long term weight loss in both groups, which is 82% in the banded group versus 63% in the not banded group. Thus sample size (n): 67, and adjust by loss sample size: 79 (10% expected loss ratio), not being necessary a 1: 1 ratio between cases and controls and requiring no more than 25 controls, A sample size of 50 cases and 30 controls, total n = 80, will be used.

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.
• Body mass index (BMI)> 40 and <55 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
• Inflammatory bowel disease
• Severe liver disease
• Digestive disease that makes unwise the bypass technique (mainly gastric illness that may required upper endoscopy for control)
• abdominal wall hernias
• Symptomatic biliary pathology that requires cholechistectomy at the same time of the bariatric surgery
• any known pathology that requieres or recomend simultaneous surgery at the time of the bariatric surgery.

We will publish the results of the study in a surgical journal