The study aims to clarify if GERD, defined by results of 24 hours potential of hydrogen (pH) monitoring and abnormal DeMeester Score (DMS), in obese patients could worsen after Sleeve Gastrectomy (SG) more than after RYGBP. To demonstrate this hypothesis, the investigators will study the obese population suspected for GERD with 24 hours monitoring and High-Resolution Esophageal Manometry (HRM). DMS is calculated pre-operatively and, once GERD is confirmed, the patients are enrolled for randomization to SG or RYGBP. The suspicion of GERD is investigated with the GERDQ score and EGDS, that all obese patients have pre-operatory.

Obesity is an independent risk factor for GERD and its complications. Bariatric surgery is effective in treatment of obesity and at the same time in controlling GERD, but there is disparity in current literature if sleeve gastrectomy could worsen it, more than gastric bypass. Our study aims to investigate if there is a difference in postoperative GERD between these two surgical procedures in obese patients with pre-existing GERD, defined by results of 24 hours pH monitoring, expressed by an abnormal DeMeester Score (DMS). REBvSS is a monocentric randomized controlled trial (RCT). The investigators will study 128 obese patients, eligible for Bariatric Surgery (BMS), suspected for GERD, with 24-h pH monitoring and high-resolution manometry. DMS is calculated pre-operatively and, once GERD is confirmed, the patients are randomized to SG or RYGBP. The DMS is then calculated on 24 hours pH monitoring 24 months after the surgery and the degree of GERD is evaluated. The promoter centre is the Division of Minimally invasive Oncological General Surgery at Azienda Socio Sanitaria Territoriale Grande Ospedale Metropolitano Niguarda, Milan, Lombardy, that is an excellence centre for bariatric and metabolic surgery according to Società Italiana di Chirurgia dell'Obesità e delle malattie metaboliche (SICOB) accreditation policy, where the study will be carried out.

Medical history will be collected during the first outpatient examination and assessed as follows:

• Diagnosis of Obesity, based on value of BMI ≥ 35;
• Investigation of obesity-related diseases
• Clinical, nutritional and surgical history
• GERDQ score If the patient is eligible for BMS and there is the suspicion of GERD the preoperative evaluation will be carried out. It consists of a trial specific evaluation (EGDS, 24-h pH monitoring, HRM, DMS), that confirms the presence of GERD, and a standard evaluation (Ultrasonography of abdomen, ECG, Chest X-Ray, Blood exams, anesthaesiologic evaluation). When all the inclusion criteria are verified, the patient will be randomized to RYGBP or SG group and will undergo surgery. All patients will be randomized centrally using an online computer controlled permuted-block randomization module between SG and RYGBP in a 1:1 ratio.

The postoperative visits will be organised as follow:

• 90 days after surgery, to evaluate the presence or the absence of medical or surgical complications;
• 12 months and 24 months after surgery EGDS, 24 hours pH-monitoring and HRM will be performed to evaluate the degree of esophagitis and calculate the DMS; the quality of life and the symptoms will be assessed troughs BAROS and GERDQ score; also the trend of comorbidities will be examined.

Every patient will be analysed according to the allocated treatment. The investigators hope that our study will finally answer this issue, thanks to its randomized nature and the definition of GERD based on gold standard pH monitoring. These findings might influence decision-making in bariatric surgery and change or confirm the success of sleeve gastrectomy, also for what concerns the reflux disease.

Inclusion Criteria:

• Acceptance of randomization to surgery;
• Participant is willing and able to give informed consent for participation in the trial;
• Written informed consent;
• Compliance to follow-up;
• Male and female;
• ≥18 and ≤70 years old;
• BMI ≥ 35 with obesity-related comorbidities;
• BMI ≥ 40 with or without obesity-related comorbidities;
• GERDQ score ≥ 3 points;
• Use of proton pump inhibitor;
• Mild and Moderate GERD (DMS ≥14.72 ≤100)
• Incompetence of the Esophagogastric junction
• Los Angeles grade A, B, C, D esophagitis.

Exclusion criteria

• Medical or psychiatric conditions that compromises the patient's ability to give informed consent or comply with the study protocol;
• Barrett's esophagus (BE);
• Spastic motor disorders and esophageal hypomotility;
• Peptic strictures;
• Absence of GERD (DMS<14.72);
• Severe GERD (DMS>100);
• Hiatal hernia > 5 cm;
• Previous bariatric surgery or major general surgery;
• Type 2 diabetes (T2D) for more than > 5 years;
• Necessity to explore stomach, the duodenum or the biliary tract;
• Refuse of randomization;
• Personal reasons.