Bariatric Surgery and Gut Microbiota Changes Over Time

NCT07381140 | Not Yet Recruiting

• 1 other identifier: RC2026-30
• Study Type: observational
• Target: 100
• Locations: 1 country
• Sites: 1

Brief Summary

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

Conditions

Gut Microbiota; Obese Patients; Obese Patients With Bariatric Surgery; Healthy Participants

Keywords

gut microbiota; stool metabolome; obesity; bariatric surgery; Roux-en-Y gastric bypass; Long-read sequencing

Outcome Measures

Primary Outcomes (1)

• Long-Term Changes in Gut Microbiota After Bariatric Surgery

  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 Outcomes (3)

• Comparison of Short- and Long-Read 16S Sequencing

  from enrollment up to 12 months of follow-up

• Fecal Metabolome Changes and Predictive Microbe-Metabolite Signatures After Bariatric Surgery

  from enrollment up to 12 months of follow-up

• Association Between Gut Microbiota and Clinical Outcomes

  from enrollment up to 12 months of follow-up

Study Arms (3)

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.

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.

Eligibility Criteria

• Age: 18 Years - 65 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)
• Sampling Method: Non-Probability Sample

Study Population

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

You may qualify if:

• 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.

You may not qualify if:

• 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.
• 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.
• Use of antibiotics within the last 3 weeks or probiotics/prebiotics within the last 4-6 weeks.
• Recent gastrointestinal surgery.

Sponsors & Collaborators

• Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de Bellis: lead

Study Sites (1)

Azienda Ospedaliera Specializzata in Gastroenterologia Saverio de Bellis

Castellana Grotte, BA, 70013, Italy

Location

Related Publications (5)

• Zhang T, Li H, Ma S, Cao J, Liao H, Huang Q, Chen W. The newest Oxford Nanopore R10.4.1 full-length 16S rRNA sequencing enables the accurate resolution of species-level microbial community profiling. Appl Environ Microbiol. 2023 Oct 31;89(10):e0060523. doi: 10.1128/aem.00605-23. Epub 2023 Oct 6.

  PMID: 37800969 BACKGROUND

• Oehler JB, Wright H, Stark Z, Mallett AJ, Schmitz U. The application of long-read sequencing in clinical settings. Hum Genomics. 2023 Aug 8;17(1):73. doi: 10.1186/s40246-023-00522-3.

  PMID: 37553611 BACKGROUND

• Salazar N, Ponce-Alonso M, Garriga M, Sanchez-Carrillo S, Hernandez-Barranco AM, Redruello B, Fernandez M, Botella-Carretero JI, Vega-Pinero B, Galeano J, Zamora J, Ferrer M, de Los Reyes-Gavilan CG, Del Campo R. Fecal Metabolome and Bacterial Composition in Severe Obesity: Impact of Diet and Bariatric Surgery. Gut Microbes. 2022 Jan-Dec;14(1):2106102. doi: 10.1080/19490976.2022.2106102.

  PMID: 35903014 BACKGROUND

• Palleja A, Kashani A, Allin KH, Nielsen T, Zhang C, Li Y, Brach T, Liang S, Feng Q, Jorgensen NB, Bojsen-Moller KN, Dirksen C, Burgdorf KS, Holst JJ, Madsbad S, Wang J, Pedersen O, Hansen T, Arumugam M. Roux-en-Y gastric bypass surgery of morbidly obese patients induces swift and persistent changes of the individual gut microbiota. Genome Med. 2016 Jun 15;8(1):67. doi: 10.1186/s13073-016-0312-1.

  PMID: 27306058 BACKGROUND

• De Luca M, Shikora S, Eisenberg D, Angrisani L, Parmar C, Alqahtani A, Aminian A, Aarts E, Brown W, Cohen RV, Di Lorenzo N, Faria SL, Goodpaster KPS, Haddad A, Herrera M, Rosenthal R, Himpens J, Iossa A, Kermansaravi M, Kow L, Kurian M, Chiappetta S, LaMasters T, Mahawar K, Merola G, Nimeri A, O'Kane M, Papasavas P, Piatto G, Ponce J, Prager G, Pratt JSA, Rogers AM, Salminen P, Steele KE, Suter M, Tolone S, Vitiello A, Zappa M, Kothari SN. Scientific Evidence for the Updated Guidelines on Indications for Metabolic and Bariatric Surgery (IFSO/ASMBS). Obes Surg. 2024 Nov;34(11):3963-4096. doi: 10.1007/s11695-024-07370-7. Epub 2024 Sep 25.

  PMID: 39320627 BACKGROUND

Biospecimen

Retention: SAMPLES WITHOUT DNA

This study will collect and retain biological samples to analyze changes in gut microbiota and metabolites in adults undergoing bariatric surgery. The following types of samples will be collected: Stool samples - collected at multiple time points before and after RYGB surgery to analyze gut bacterial composition and fecal metabolome. Blood samples - collected at the same time points to assess metabolic, inflammatory, and clinical biomarkers. Urine samples - collected for additional metabolic analyses and to complement stool and blood data. ll samples will be properly labeled, stored, and retained in accordance with applicable institutional and regulatory guidelines. Samples may be used for bacterial DNA-based sequencing analyses, metabolomic profiling, and other related laboratory assays to investigate the relationships between microbiota, metabolites, and clinical outcomes.

MeSH Terms

Conditions

Obesity

Condition Hierarchy (Ancestors)

Overweight; Overnutrition; Nutrition Disorders; Nutritional and Metabolic Diseases; Body Weight; Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Central Study Contacts

Domenica Mallardi, Biologist

CONTACT

+390804994129; domenica.mallardi@irccsdebellis.it

Francesco Russo, MD

CONTACT

+390804994129; francesco.russo@irccsdebellis.it

Study Design

• Study Type: observational
• Observational Model: CASE CONTROL
• Time Perspective: PROSPECTIVE
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Clinical Researcher (Biologist)

Study Record Dates

• First Submitted: January 23, 2026
• First Posted: February 2, 2026
• Study Start: April 1, 2026
• Primary Completion (Estimated): April 1, 2027
• Study Completion (Estimated): April 1, 2028
• Last Updated: February 5, 2026

Record last verified: 2026-02

Data Sharing

• IPD Sharing: Will not share

Locations

IT (1)