Bariatric Surgery and Gut Microbiota Changes Over Time (RYGB-MICROGUT)

February 3, 2026 updated by: Domenica Mallardi, Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de Bellis

Longitudinal Evaluation of Gut Microbiota and Fecal Metabolome Following Roux-en-Y Gastric Bypass: Clinical Implications and Identification of Predictive Biomarkers

The goal of this observational study is to learn how bariatric surgery affects gut bacteria and gut-related metabolic products over time in adults with obesity. The study includes adults aged 18 to 65 years who are undergoing Roux-en-Y gastric bypass (RYGB) surgery, as well as adults with obesity treated with diet alone and healthy normal-weight adults.

The main questions it aims to answer are:

How does bariatric surgery change the composition and diversity of gut bacteria over time? How are these changes related to weight loss and improvement of obesity-related health conditions?

Researchers will compare people undergoing bariatric surgery with people with obesity treated with diet alone and with healthy normal-weight individuals to see if surgery leads to specific changes in gut bacteria and stool metabolites that are linked to better clinical outcomes.

Participants will:

Provide stool samples at scheduled time points over 12 months Provide blood samples and undergo routine clinical assessments Take part in follow-up visits to monitor weight, metabolic health, and gastrointestinal symptoms

Study Overview

Status

Not yet recruiting

Conditions

Detailed Description

Obesity is a complex and multifactorial condition associated with metabolic, inflammatory, and gastrointestinal alterations. In recent years, the gut microbiota has emerged as a key factor involved in energy balance, metabolic regulation, and systemic inflammation. Alterations in gut microbial composition and function have been consistently observed in individuals with obesity and are thought to contribute to metabolic dysfunction.

Bariatric surgery, particularly Roux-en-Y gastric bypass (RYGB), is one of the most effective treatments for severe obesity and its related comorbidities. Beyond weight loss, this procedure induces profound changes in gastrointestinal anatomy and nutrient flow, which may significantly influence the gut microbiota and the metabolites it produces. However, the timing, persistence, and clinical relevance of these microbial and metabolic changes over the long term are not yet fully understood.

This prospective observational study is designed to evaluate longitudinal changes in gut microbiota composition and fecal metabolome following bariatric surgery and to explore their association with clinical and metabolic outcomes. Participants undergoing bariatric surgery will be followed over a 12-month period and compared with individuals with obesity receiving dietary treatment and with healthy normal-weight individuals. This comparative approach allows the identification of changes specifically related to surgery rather than to weight loss alone or to normal temporal variability.

Gut microbiota will be analyzed using DNA-based sequencing approaches, while fecal metabolites will be assessed to capture functional changes in microbial activity. These biological data will be integrated with clinical and laboratory parameters to explore relationships between gut-related changes and outcomes such as weight loss, metabolic improvement, inflammation, and intestinal barrier function.

By providing a longitudinal and integrated view of gut microbiota and metabolome remodeling after bariatric surgery, this study aims to improve understanding of the biological mechanisms underlying surgical outcomes and to support the identification of potential biomarkers that may help predict individual responses and guide more personalized approaches to obesity management.

Study Type

Observational

Enrollment (Estimated)

100

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • Italy
    • BA
      • Castellana Grotte, BA, Italy, 70013
        • Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de Bellis

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Sampling Method

Non-Probability Sample

Study Population

Obese subjects attending the clinical nutrition outpatient clinic of the IRCCS "Saverio de Bellis" - Castellana Grotte (BA).

Description

Inclusion Criteria (RYGB Group):

  • Age between 18 and 65 years.
  • Adults with a body mass index (BMI) ≥ 35 kg/m² with related comorbidities, or BMI ≥ 40 kg/m², who are candidates for Roux-en-Y gastric bypass (RYGB) surgery only.

Exclusion Criteria (RYGB Group):

  • Treatment with antibiotics within the last 3 weeks, or probiotics/prebiotics within the last 4-6 weeks, or systemic corticosteroids within the 8 weeks prior to baseline (T0).
  • Participation in dietary regimens or calorie restriction programs in the weeks prior to enrollment.
  • Chronic inflammatory bowel diseases (e.g., Crohn's disease, ulcerative colitis), ongoing enteric infections, or active neoplasms.
  • Previous organ transplant or ongoing systemic immunosuppressive therapy.
  • Pregnancy or breastfeeding.
  • Previous major gastrointestinal surgery.
  • Chronic alcohol consumption above moderate levels or substance use disorder.

Inclusion Criteria (Obese Control Group):

  • Age between 18 and 65 years.
  • Adults with BMI ≥ 30 kg/m² who are candidates for structured dietary treatment.

Inclusion Criteria (Healthy Control Group):

  • Age between 18 and 65 years.
  • Normal weight (BMI between 18.5 and 24.9 kg/m²).
  • Normal metabolic function: fasting glucose below threshold, normal ALT/AST, no diagnosis of diabetes or metabolic syndrome.
  • No chronic gastrointestinal diseases or conditions that could alter the gut microbiota.

Exclusion Criteria (Obese Control and Healthy Control Group):

  • Use of antibiotics within the last 3 weeks or probiotics/prebiotics within the last 4-6 weeks.
  • Recent gastrointestinal surgery.
  • Pregnancy or breastfeeding.
  • Extreme diets or recent dietary changes.
  • Recent international travel that could have affected the gut microbiota.
  • Medications known to influence the gut microbiota (e.g., PPIs, metformin, steroids).
  • Active smoking or excessive alcohol consumption.
  • Significant gastrointestinal symptoms (chronic diarrhea or constipation).

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Obese Control Group
Adults aged 18-65 years with obesity (BMI ≥ 30 kg/m²) who are receiving structured dietary treatment without surgery.
Healthy Control Group
Adults aged 18-65 years with normal weight (BMI 18.5-24.9 kg/m²) and normal metabolic function. This group helps identify normal variations in gut bacteria and metabolites over time, independent of obesity or surgery.
RYGB Group
Adults aged 18-65 years with severe obesity (BMI ≥ 35 kg/m² with comorbidities or BMI ≥ 40 kg/m²) who are undergoing Roux-en-Y gastric bypass (RYGB) surgery.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Long-Term Changes in Gut Microbiota After Bariatric Surgery
Time Frame: from enrollment up to 12 months of follow-up
Longitudinal changes in the composition and diversity of the gut microbiota (alpha diversity, beta diversity, and relative abundance of key bacterial taxa) in patients undergoing Roux-en-Y gastric bypass (RYGB) surgery, assessed using 16S rRNA gene sequencing (short-read and full-length), compared with the Obese Control and Healthy Control groups.
from enrollment up to 12 months of follow-up

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Comparison of Short- and Long-Read 16S Sequencing
Time Frame: from enrollment up to 12 months of follow-up
Compare the performance of short-read (V3-V4) and long-read (full-length 16S rRNA) sequencing technologies in terms of taxonomic resolution and biomarker identification.
from enrollment up to 12 months of follow-up
Fecal Metabolome Changes and Predictive Microbe-Metabolite Signatures After Bariatric Surgery
Time Frame: from enrollment up to 12 months of follow-up
Assess changes in the fecal metabolome over time after bariatric surgery and Identify microbe-metabolite signatures predictive of clinical response to bariatric surgery.
from enrollment up to 12 months of follow-up
Association Between Gut Microbiota and Clinical Outcomes
Time Frame: from enrollment up to 12 months of follow-up
Analyze the association between gut microbiota changes and clinical/metabolic parameters (weight loss, comorbidities, inflammatory and intestinal permeability markers)
from enrollment up to 12 months of follow-up

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de Bellis

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

April 1, 2026

Primary Completion (Estimated)

April 1, 2027

Study Completion (Estimated)

April 1, 2028

Study Registration Dates

First Submitted

January 23, 2026

First Submitted That Met QC Criteria

January 23, 2026

First Posted (Actual)

February 2, 2026

Study Record Updates

Last Update Posted (Actual)

February 5, 2026

Last Update Submitted That Met QC Criteria

February 3, 2026

Last Verified

February 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • RC2026-30

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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