Effect of Omeprazole on Gut Microbiota in Adults With Obesity and GERD

This randomized, open-label, parallel-group study will evaluate the effect of short-term omeprazole therapy on gut and oral microbiota in adults aged 50-65 years with obesity and symptomatic gastroesophageal reflux disease. Participants will be randomized 1:1 to receive omeprazole 20 mg once daily for 14 days plus standard non-pharmacological recommendations for gastroesophageal reflux disease, or standard non-pharmacological recommendations alone. Clinical and laboratory assessments will be performed at baseline and after 14 days. Stool and saliva samples will be collected to assess gut and oral microbiota, and blood samples will be collected for laboratory biomarkers.

Inclusion Criteria: * Age 50 to 65 years, inclusive. * Obesity, defined as body mass index (BMI) ≥30 kg/m². * Symptomatic gastroesophageal reflux disease with mild or moderate typical symptoms, including heartburn and/or regurgitation. * For female participants, postmenopausal status, defined as absence of menstruation for at least 12 months without another apparent cause of amenorrhea. * Written informed consent to participate in the study. Exclusion Criteria: * Severe or exacerbated GERD, or GERD requiring acid-suppressive therapy or additional diagnostic evaluation. * Use of proton pump inhibitors or histamine H2-receptor antagonists within 8 weeks prior to enrollment. * Use of systemic antibiotics within 3 months prior to enrollment. * Use of probiotic or synbiotic supplements within 8 weeks prior to enrollment. * Inflammatory bowel disease, celiac disease, or other severe chronic gastrointestinal disorders that may substantially affect the gut microbiota. * History of bariatric surgery or other major gastrointestinal surgery. * Acute infectious or inflammatory disease at enrollment. * History of myocardial infarction or stroke. * Type 2 diabetes mellitus. * Chronic heart failure, New York Heart Association functional class III-IV. * Chronic kidney disease with estimated glomerular filtration rate \