Stool Analysis After Sleeve Gastrectomy vs Gastric Bypass

Routine Stool Parameters Six Months After Sleeve Gastrectomy vs. Gastric Bypass: Correlation With Weight Loss and Metabolic Outcomes

The goal of this observational study is to learn whether routine stool tests can detect changes in gut function 6 months after two common types of weight loss surgery: sleeve gastrectomy and gastric bypass (including mini gastric bypass and Roux-en-Y gastric bypass). The main questions it aims to answer are:

Do stool tests show more signs of undigested food or carbohydrate malabsorption after gastric bypass compared to sleeve gastrectomy?

Do signs of gut inflammation in stool (like fecal calprotectin) decrease after surgery, and does this relate to improvements in blood sugar and weight loss?

Can simple stool test results at 6 months predict how much weight a person loses or how well their diabetes improves?

Researchers will compare stool test results between the two surgery groups (sleeve gastrectomy vs. gastric bypass) to see if the type of surgery leads to different changes in gut health.

Participants will:

Provide a stool sample before surgery and again 6 months after surgery

Provide a blood sample at the same time points to measure weight, blood sugar, and cholesterol

Undergo their planned weight loss surgery as part of their regular medical care

Study Overview

• Status: Recruiting
• Conditions: Morbid Obesity
• Intervention / Treatment: Procedure: Laparoscopic Sleeve Gastrectomy; Procedure: Mini Gastric Bypass; Procedure: Roux-en-Y Gastric Bypass

Detailed Description

Background:

Obesity is a global pandemic with rising incidence, contributing significantly to morbidity, mortality, and healthcare costs worldwide. Bariatric surgery, particularly sleeve gastrectomy (SG) and gastric bypass procedures (including Mini Gastric Bypass [MGB] and Roux-en-Y Gastric Bypass [RYGB]), remains the most effective and durable treatment for morbid obesity, achieving sustained weight loss and remission of metabolic comorbidities such as type 2 diabetes.

The gastrointestinal tract, particularly the gut microbiome, has emerged as a key metabolic regulator. Obesity is associated with dysbiosis-reduced microbial diversity and altered predominance of bacterial phyla-which contributes to systemic inflammation, insulin resistance, and metabolic syndrome. Bariatric surgery induces profound and durable changes in the gut environment, including alterations in gastric emptying, intestinal transit time, bile acid signaling, and the composition of the gut microbiota.

However, advanced microbiome sequencing is expensive, time-consuming, and not readily available in many clinical settings. Routine stool analysis, by contrast, is a simple, inexpensive, and universally available test that can provide valuable preliminary data on gut health. Parameters such as stool pH, the presence of leukocytes, undigested food particles, and quantitative markers like fecal calprotectin and reducing substances can offer indirect evidence of maldigestion, mucosal inflammation, and microbial activity.

Objective:

The primary objective is to compare changes in routine stool parameters (physical examination, microscopic examination, undigested food particles, fecal calprotectin, and reducing substances) from baseline to 6 months postoperatively between patients undergoing SG and those undergoing Gastric Bypass (MGB or RYGB).

Secondary objectives include: correlating postoperative changes in stool parameters with clinical outcomes (%TWL, diabetes remission, changes in HbA1c and lipid profile); comparing the prevalence of specific stool findings between groups; evaluating whether baseline stool parameters can predict postoperative outcomes; and assessing the utility of routine stool analysis as a simple, low-cost tool for monitoring gut health after bariatric surgery.

Methods:

This is a prospective, two-arm, observational cohort study conducted at the Department of General Surgery, Kasr Al-Ainy University Hospitals, Cairo, Egypt. The study period is from March 2026 to December 2026.

Study Timeline and Data Collection:

Patients will be assessed at two predefined time points:

T0 (Baseline): 1-2 weeks preoperatively - informed consent, demographic data, medical history, anthropometric measurements, blood samples, stool sample

T1 (6 months): 6 months ± 2 weeks postoperatively - anthropometric measurements, blood samples, stool sample, assessment of comorbidities, final outcomes

Clinical and Anthropometric Measurements:

Body weight (kg) and height (m) for BMI calculation (kg/m²)

Percentage total weight loss (%TWL) at 6 months = [(initial weight - 6-month weight) / initial weight] × 100

Presence and status of comorbidities (diabetes, hypertension, dyslipidemia)

Diabetes remission defined as HbA1c < 6.5% off all antidiabetic medications at 6 months

A total of 46 patients with morbid obesity (BMI ≥40 or ≥35 kg/m² with comorbidities) scheduled for primary laparoscopic bariatric surgery will be enrolled and allocated into two groups: Group A (SG, n=23) and Group B (Gastric Bypass [MGB or RYGB], n=23). The type of gastric bypass (MGB vs. RYGB) will be determined by the surgical team based on patient anatomy, comorbidities, and surgeon preference, reflecting real-world clinical practice.

Blood Sampling and Biochemical Analysis:

After an overnight fast (8-12 hours), venous blood will be collected at both time points for:

• Fasting plasma glucose (mg/dL)
• Glycated hemoglobin (HbA1c %)
• Lipid profile: total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides (mg/dL)
• High-sensitivity C-reactive protein (hs-CRP) (mg/L) as a marker of systemic inflammation

Stool Sample Collection and Analysis:

Patients will be provided with a sterile, leak-proof stool collection container and written instructions. They will collect a fresh morning stool sample at home. Samples should be transported to the hospital laboratory within 2 hours of collection. If immediate transport is not possible, samples should be refrigerated (4°C) and transported within 12 hours.

Stool analysis parameters include:

Physical Examination: Color, consistency, odor, mucus, pH

Microscopic Examination: White Blood Cells (WBCs), Red Blood Cells (RBCs), trophozoites, cysts, ova, larva, flagellates, ciliate

Undigested Food Particles: Meat fibers, vegetable particles, starch granules, fat globules

Quantitative Tests: Fecal calprotectin (ELISA), Reducing substances (Clinitest tablets)

• Study Type: Observational
• Enrollment (Estimated): 50

Contacts and Locations

• Study Contact: Name: Ahmed Eid Aziz, Lecturer; Phone Number: +201127060844; Email: Ahmed-eid@kasralainy.edu.eg

Study Locations

• Egypt
  • Al-Manial Cairo
    • Cairo, Al-Manial Cairo, Egypt, 11956
      • Recruiting
      • Faculty of medicine Cairo University
      • Contact: Mahmoud El Azhary, Lecturer; Phone Number: +201064110221; Email: Mahmoud.azhary@kasralainy.edu.eg

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Patients with morbid obesity scheduled for primary bariatric surgery at Kasr Al-Ainy University Hospitals, Cairo, Egypt.

Description

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

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Sleeve Gastrectomy (SG); Patients undergoing primary laparoscopic sleeve gastrectomy as treatment for morbid obesity. This group serves as the restrictive procedure comparator.	Procedure: Laparoscopic Sleeve Gastrectomy; Laparoscopic sleeve gastrectomy performed using a standard technique with a 36-Fr bougie, transecting the stomach starting 4-6 cm from the pylorus, excising the entire greater curvature and fundus. The staple line is inspected for hemostasis and leakage.
Gastric Bypass (MGB/RYGB); Patients undergoing primary laparoscopic gastric bypass, including both Mini Gastric Bypass (MGB) and Roux-en-Y Gastric Bypass (RYGB), as treatment for morbid obesity. This group serves as the diversionary procedure comparator.	Procedure: Mini Gastric Bypass; Laparoscopic mini gastric bypass performed using a standard technique with a long gastric tube created from the angle of His to the antrum, and a loop gastrojejunostomy with a biliopancreatic limb of 200 cm.; Procedure: Roux-en-Y Gastric Bypass; Laparoscopic Roux-en-Y gastric bypass performed using a standard antecolic, antegastric technique. A small 30-mL gastric pouch is created. The biliopancreatic limb is 70-150 cm, and the alimentary (Roux) limb is 100-150 cm. Jejunojejunostomy is performed to restore continuity.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Stool pH	Change in stool pH measured by pH indicator strip from preoperative baseline to 6 months after surgery. Comparison will be made between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Change in Fecal Calprotectin Level	Change in fecal calprotectin concentration (μg/g) measured by ELISA from preoperative baseline to 6 months after surgery. Comparison will be made between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Presence of Undigested Food Particles	Presence or absence of undigested meat fibers and vegetable particles on microscopic examination at 6 months after surgery. Comparison of prevalence between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Presence of Reducing Substances	Presence or absence of reducing substances (indicating carbohydrate malabsorption) measured by Clinitest tablets at 6 months after surgery. Comparison of prevalence between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Change in Stool White Blood Cell Count	Change in white blood cell count (cells per high-power field) on microscopic examination from preoperative baseline to 6 months after surgery. Comparison will be made between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Change in Stool Red Blood Cell Count	Change in red blood cell count (cells per high-power field) on microscopic examination from preoperative baseline to 6 months after surgery. Presence of RBCs may indicate mucosal irritation at staple lines or altered barrier function. Comparison will be made between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Percentage Total Weight Loss (%TWL)	Percentage total weight loss calculated as [(initial weight - 6-month weight) / initial weight] × 100. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	6 months postoperatively
Diabetes Remission Rate	Proportion of patients with type 2 diabetes at baseline who achieve remission, defined as HbA1c < 6.5% off all antidiabetic medications at 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	6 months postoperatively
Change in Fasting Plasma Glucose	Change in fasting plasma glucose (mg/dL) from preoperative baseline to 6 months after surgery	At Baseline and at 6 months postoperatively
Change in HbA1c	Change in glycated hemoglobin (HbA1c %) from preoperative baseline to 6 months after surgery.	At Baseline and at 6 months postoperatively
Change in Lipid Profile	Changes in total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides (mg/dL) from preoperative baseline to 6 months after surgery.	At Baseline and at 6 months postoperatively
Change in High-Sensitivity C-Reactive Protein (hs-CRP)	Change in hs-CRP (mg/L) from preoperative baseline to 6 months after surgery as a marker of systemic inflammation.	At Baseline and at 6 months postoperatively
Correlation Between Stool Parameters and Clinical Outcomes	Correlation between changes in stool parameters (WBC count, RBC count, pH, fecal calprotectin, reducing substances, undigested food particles, mucus, trophozoites, cysts, ova, larva, flagellates, ciliates) and clinical outcomes (%TWL, change in HbA1c) using Spearman's rank correlation coefficient.	6 months postoperatively
Prevalence of Elevated Fecal Calprotectin	Prevalence of elevated fecal calprotectin (>50 μg/g) in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Positive Reducing Substances	Prevalence of positive reducing substances (indicating carbohydrate malabsorption) in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Mucus in Stool	Prevalence of visible mucus on physical examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Elevated White Blood Cells in Stool	Prevalence of elevated white blood cells (>10 per high-power field) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Elevated Red Blood Cells in Stool	Prevalence of elevated red blood cells (>5 per high-power field) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Trophozoites in Stool	Prevalence of trophozoites (any) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Cysts in Stool	Prevalence of cysts (any) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Ova in Stool	Prevalence of ova (any) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Larva in Stool	Prevalence of larva (any) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Flagellates in Stool	Prevalence of flagellates (e.g., Giardia) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively
Prevalence of Ciliates in Stool	Prevalence of ciliates (e.g., Balantidium coli) on microscopic examination in each group at baseline and 6 months postoperatively. Comparison between Sleeve Gastrectomy (SG) and Gastric Bypass (MGB/RYGB) groups.	At Baseline and at 6 months postoperatively

Collaborators and Investigators

• Sponsor: Cairo University

Study record dates

Study Major Dates

• Study Start (Actual): April 5, 2026
• Primary Completion (Estimated): November 1, 2026
• Study Completion (Estimated): December 1, 2026

Study Registration Dates

• First Submitted: March 4, 2026
• First Submitted That Met QC Criteria: March 6, 2026
• First Posted (Actual): March 10, 2026

Study Record Updates

• Last Update Posted (Actual): May 18, 2026
• Last Update Submitted That Met QC Criteria: May 14, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Fecal Calprotectin; Bariatric Surgery; Gut Microbiota; Stool Analysis; Reducing Substances; Maldigestion
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Overweight; Obesity; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity, Morbid; Therapeutics; Surgical Procedures, Operative; Digestive System Surgical Procedures; Anastomosis, Surgical; Bariatric Surgery; Bariatrics; Obesity Management; Gastroenterostomy; Gastric Bypass
• Other Study ID Numbers: Ms-48-2026

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No