This study follows patients who have undergone one-anastomosis gastric bypass (OAGB), a type of weight-loss surgery, to check for changes in the stomach and esophagus over time. All patients have an upper endoscopy before surgery and then again 1, 3, and 5 years later, even if they have no symptoms. The main goal is to see how often problems like bile reflux or ulcers at the surgical join (marginal ulcers) occur. The study also looks at whether patients' symptoms match what is seen during endoscopy.

This study is designed to learn more about changes in the digestive system after one-anastomosis gastric bypass (OAGB), a widely used weight-loss operation. While this surgery is effective for reducing excess weight and improving obesity-related health problems, some people may develop changes in the stomach or esophagus over time, such as bile reflux (backflow of bile into the stomach or esophagus) or marginal ulcers (sores at the site where the stomach is joined to the small intestine).

To better understand how often these problems occur, and whether they cause symptoms, the study follows patients for at least 5 years after surgery. All participants have an upper endoscopy (a camera test that looks at the esophagus, stomach, and the join with the small intestine) before surgery, and then again 1, 3, and 5 years afterwards. These check-ups are done even if the patient feels well, to detect any hidden changes early.

The study also compares what patients report in symptom questionnaires-covering issues like heartburn, regurgitation, or stomach discomfort-with what is actually seen during endoscopy. This will help doctors understand how well symptoms match the real condition of the digestive tract.

By using the same protocol across several specialized bariatric centers, and including all eligible patients, the study aims to provide reliable, long-term data to guide follow-up care after OAGB. The findings could help refine patient monitoring, improve early detection of problems, and identify risk factors that can be addressed to prevent complications.

Inclusion Criteria:

• • Age ≥ 18 years.

  • Meets IFSO indications for bariatric surgery (BMI > 40 kg/m², or BMI > 35 kg/m² with obesity-related comorbidities).
  • Candidate for primary one-anastomosis gastric bypass (OAGB).
  • Preoperative upper endoscopy completed as part of standardized work-up.
  • Helicobacter pylori screened preoperatively and (if positive) eradication therapy completed before surgery.
  • Able and willing to attend scheduled postoperative upper endoscopies (at approximately 1, 3, and 5 years) regardless of symptoms.
  • Able to complete patient-reported outcome instruments (GERD-HRQL and abbreviated GSRS).
  • Provided written informed consent.

• Major postoperative complication within 30 days after OAGB (Clavien-Dindo grade III or IV).
• Any subsequent abdominal surgery after OAGB (e.g., cholecystectomy, incisional hernia repair) prior to planned endoscopic follow-up.
• Prior or concomitant revisional bariatric procedure that could impair esophageal motility.
• Total clinical follow-up shorter than 12 months.
• Chronic corticosteroid use.
• Chronic nonsteroidal anti-inflammatory drug (NSAID) use.
• Preoperative upper endoscopy showing Los Angeles grade ≥ B esophagitis.
• Preoperative hiatal hernia > 5 cm.
• Severe, proton-pump-inhibitor-resistant GERD symptoms or advanced lower esophageal sphincter (LES) incompetence preoperatively.
• Inability or unwillingness to provide informed consent or comply with follow-up.