Background While several articles have reported about the effects of laparoscopic sleeve gastrectomy (LSG) on the lower esophageal sphincter (LES), to date, just one paper has discussed this issue with regard the Mini/One anastomosis gastric bypass (MGB/OAGB). This is expected to be the first randomized trial exploring and comparing these two interventions.

Setting "Federico II" University Hospital, Naples - ITALY.

Methods Fifty morbid obese patients are going to be studied. All patients presenting with a normal preoperative LES function will be randomly assigned to undergo LSG (arm 1 - 25 pts) or MGB (arm 2 - 25 pts). Patients undergo clinical assessment for reflux symptoms, and esophago-gastro-duodenoscopy (EGDS) plus high-resolution impedance manometry (HRiM) and 24-hour pH-impedance monitoring (MII-pH) before, two months and 1 year after both LSG or MGB/OAGB.

Objective Endpoint 1: Does this surgery affect the LES area function in both arm 1 or arm 2 patients determining a possible increase in gastroesophageal acid or non acid reflux? Endpoint 2: Does one between the two procedures outperform the other one in terms of eventual LES area modifications? Endpoint 3: In the case of a good performance of LSG or MGB/OAGB or both the procedures, is this to be primarily related to surgery per se or to weight loss?

Inclusion Criteria:

• 80 morbid obese patients are going to be studied. All patients presenting with a normal preoperative LES function will be randomly assigned to undergo LSG (arm 1 - 40 pts) or MGB (arm 2 - 40 pts).-

Exclusion Criteria:

• Patients lost at follow up. Cancer patients at any stage.