Gut Bacteria Changes Over Time After Weight-Loss Surgery
Follows gut bacteria in adults with obesity after gastric bypass surgery over time.
Plain-language title generated from the registry record
Registry title: Bariatric Surgery and Gut Microbiota Changes Over Time
Key facts
- Where
- Castellana Grotte, ItalySee the site
AI summary: who the study is looking for
From the trial's eligibility criteria. Machine-read from the registry text on this page, so it can be wrong. The registry text below and the trial team decide who can take part.
The trial is looking for adults with obesity who are having Roux-en-Y gastric bypass surgery. It also takes adults with obesity on a diet alone, and healthy normal-weight adults.
- Age
- 18 to 65 years
- Sex
- All sexes can join.
- Disease stage
- Surgery group: BMI 35 kg/m² or more with related health problems, or BMI 40 kg/m² or more, and a candidate for Roux-en-Y gastric bypass. Diet group: BMI 30 kg/m² or more, a candidate for structured diet treatment. Healthy group: BMI between 18.5 and 24.9 kg/m², normal metabolic function, no diabetes or metabolic syndrome.
- Earlier treatment
- Cannot have taken antibiotics in the last 3 weeks or probiotics/prebiotics in the last 4-6 weeks. Surgery group: no systemic corticosteroids in the 8 weeks before the start, and no diet or calorie restriction programs in the weeks before joining.
Main reasons for not taking part
- Antibiotics, probiotics or prebiotics taken recently
- Pregnancy or breastfeeding
- Previous or recent gastrointestinal surgery
- Inflammatory bowel disease, ongoing gut infections or active cancer (surgery group)
- Medicines that affect gut bacteria, such as PPIs, metformin or steroids (diet and healthy groups)
Read by machine on 9 November 2026.
Could this be for you?
Answer for yourself. This is not a decision: only the study team can say whether you can take part.
- Are you between 18 and 65 years old?
Source: NCT07381140, who can take part
Where in Italy
- Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de BellisCastellana Grotte, ItalyContact: Domenica Mallardi, BiologistTaking people
Questions to ask the study team
- How often do I need to come in, and for how long each time?
- Are travel costs paid?
- Can I keep my own doctor?
- What happens if I want to stop?
Contact the study team: see the registry record → Contacts and Locations
Print a page for my doctorTrial details
- Who runs it
- Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de Bellis
- Trial code
- NCT07381140
- Record updated
- 5 November 2026
- Original description
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.Read full original descriptionShow less
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
Inclusion: 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; Age between 18 and 65 years; Adults with BMI ≥ 30 kg/m² who are candidates for structured dietary treatment; 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: 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; Previous organ transplant or ongoing systemic immunosuppressive therapy; Previous major gastrointestinal surgery; Recent gastrointestinal surgery; Medications known to influence the gut microbiota (e.g., PPIs, metformin, steroids); Chronic inflammatory bowel diseases (e.g., Crohn's disease, ulcerative colitis), ongoing enteric infections, or active neoplasms; Chronic alcohol consumption above moderate levels or substance use disorder; Pregnancy or breastfeeding; Use of antibiotics within the last 3 weeks or probiotics/prebiotics within the last 4-6 weeks; Pregnancy or breastfeeding; Extreme diets or recent dietary changes; Recent international travel that could have affected the gut microbiota; Active smoking or excessive alcohol consumption; Significant gastrointestinal symptoms (chronic diarrhea or constipation).