Stool Analysis After Sleeve Gastrectomy vs Gastric Bypass

Inclusion Criteria: * Male and female patients aged 18 to 60 years * Body Mass Index (BMI) ≥ 40 kg/m², OR BMI ≥ 35 kg/m² with at least one obesity-related comorbidity (type 2 diabetes, hypertension, dyslipidemia, osteoarthritis, obstructive sleep apnea) * Patients scheduled for primary laparoscopic bariatric surgery (either SG or Gastric Bypass \[MGB or RYGB\]) at Kasr Al-Ainy University Hospitals * Provision of written informed consent Exclusion Criteria: * Age \< 18 years or \> 60 years * Previous bariatric surgery or major gastrointestinal surgery (gastric, intestinal, or colorectal resection) * Chronic kidney disease (eGFR \< 60 mL/min/1.73m²) or previous renal transplant * Chronic liver disease (cirrhosis, chronic hepatitis) or liver failure * Chronic inflammatory bowel disease (Crohn's disease, ulcerative colitis), celiac disease, or chronic pancreatitis * Active malignancy or history of chemotherapy/radiotherapy in the past 5 years * Pregnancy or breastfeeding * Chronic alcohol abuse or substance abuse * Use of antibiotics, probiotics, or prebiotics within 4 weeks prior to stool sample collection (to avoid confounding effects on gut flora) * Acute gastrointestinal infection at the time of sample collection