Obese Patients With Bariatric SurgeryMICROOBARNCT07277465
Role of the Microbiota in Obesity: Effect After Bariatric Surgery
A study testing Bariatric surgery in people with Obese Patients With Bariatric Surgery, run by Celia Bañuls at 1 site in Spain.
Trial summary
Several studies have demonstrated that bariatric surgery is effective for inducing weight loss in obese patients. In addition, the effects of this surgery on multiple associated alterations are well known, including changes in the secretion and activity of hormones involved in appetite regulation, satiety, and energy… Read more about this study
- Who is it for?
- Ages 18 to 65 years
- Conditions the study is for
- Obese Patients With Bariatric Surgery
- What is being tested?
- Bariatric surgery
- Type of treatment
- Surgery or procedure
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 60 participants
- Where
- 1 siteSpain
- Study dates
- 3 Mar 2021to 31 May 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 65 years
- All sexes
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Patients with a body mass index (BMI) greater than 40 kg/m² (or > 35 kg/m² with minimum one obesity comorbidity).
- Aged between 18 and 65 years.
- Patients with a known duration of obesity exceeding five years, despite dietary interventions and farmacological treatment.
Who cannot join
- Due to the nature of the study, patients with acute or chronic inflammatory diseases, established hepatic or renal insufficiency (defined as transaminase levels ±2 SD from the mean and estimated glomerular filtration rate [CKD-EPI formula] >60), neoplasic diseases, or secondary causes of obesity (e.g., hypothyroidism, Cushing's syndrome) will be excluded.
Trial locations and contacts
1 site in 1 country.
About this study
Several studies have demonstrated that bariatric surgery is effective for inducing weight loss in obese patients. In addition, the effects of this surgery on multiple associated alterations are well known, including changes in the secretion and activity of hormones involved in appetite regulation, satiety, and energy expenditure, as well as alterations in the gut microbiota composition.
However, in cases of severe obesity, recent data have challenged the prevailing view, as bacterial species associated with low microbial richness (prior to surgery) appear to change only marginally after bariatric surgery, despite significant metabolic improvements.
Read more
Our objective is to examine whether gut microbiota and gastrointestinal peptides are further impaired in severe obesity and, additionally, to explore how the microbiota relates to metabolic profile or sex, as well as whether bariatric surgery may differentially correct obesity-related intestinal microbial features.
To this end, we propose a prospective, interventional, translational clinical study involving a cohort of 60 obese patients (BMI > 35 kg/m²) undergoing laparoscopic gastric bypass surgery. Patients will be grouped according to their degree of obesity to assess potential baseline differences and to evaluate the efficacy of the intervention. Furthermore, we will investigate whether these parameters differ according to metabolic profile or sex.
Body composition and nutritional status will be assessed, along with cardiovascular risk factors and comorbidities (hypertension, obstructive sleep apnea syndrome, dyslipidemia, type 2 diabetes mellitus, and insulin resistance). Gastrointestinal hormones (ghrelin, GIP, GLP-1, PYY, CCK, and leptin) will be measured in serum using Luminex XMAP technology. The content and diversity of the gut microbiota will be analyzed (16S rRNA amplicon sequencing and shotgun metagenomic sequencing using Illumina MiSeq technology) in stool samples collected before and 6-12 months after surgery. Additionally, individualized dietary follow-up and assessment of participants' quality of life will be conducted.
Read the detailed description
Obesity and type 2 diabetes mellitus (T2DM) continue to increase worldwide and are strongly associated with adverse metabolic and cardiovascular outcomes. Bariatric surgery, particularly laparoscopic gastric bypass (LGB), remains the most effective therapeutic strategy for substantial weight reduction, glycemic improvement, and favorable modulation of gastrointestinal hormones, bile acids, and gut microbiota. Nevertheless, the mechanisms explaining heterogeneous metabolic responses-especially in individuals with severe, morbid, or extreme obesity-remain insufficiently elucidated. In particular, gut microbial diversity, microbial gene richness, and related inflammatory pathways appear to contribute to metabolic health, yet their behavior in severe obesity and their evolution following bariatric surgery remain poorly characterized.
To address these gaps, the investigators designed a prospective, interventional, comparative, and translational clinical study including 60 obese individuals scheduled for bariatric surgery at a single tertiary hospital. Participants will be consecutively recruited according to strict inclusion and exclusion criteria and classified by degree of adiposity (severe, morbid, or extreme obesity), metabolic phenotype (metabolically healthy or metabolically abnormal obesity), and sex.
Prior to the surgical intervention, a structured dietary protocol will be implemented. Participants will receive an individualized hypocaloric diet tailored to nutritional requirements, with a macronutrient distribution of 55% carbohydrates, 30% fats, and 15% proteins. During the two weeks preceding surgery, a very low-calorie diet based on Optisource® sachets will be administered in three daily intakes. Postoperative dietary progression will follow standardized clinical guidelines, with close monitoring to support weight reduction and metabolic stabilization. Follow-up evaluations will occur at 1, 6, and 12 months after surgery.
All participants will undergo comprehensive baseline and longitudinal assessments, including: evaluation of nutritional status; anthropometric measurements; body composition and basal metabolism; cardiovascular risk factors; metabolic comorbidities; and exclusion of secondary causes of obesity. Analytical parameters will include fasting plasma glucose, lipid profile (triglycerides, HDL-cholesterol), blood pressure, markers of hepatic and renal function, and additional biochemical indices relevant to obesity and T2DM risk stratification. Gut microbiota profiling will be conducted to evaluate microbial composition, diversity, and gene richness. Gastrointestinal hormone analyses will quantify circulating incretins and appetite-regulating peptides, including GLP-1, PYY, and ghrelin, to explore their association with postoperative metabolic outcomes. Oxidative stress and inflammatory parameters will be also assessed in order to stratify cardiovascular risk before and after induced weight loss after bariatric surgery.
Statistical analyses will be performed using SPSS 17.0. Categorical variables will be summarized with frequency distributions and percentages. Quantitative variables will be described using mean, range, and standard deviation, with normality assessed via the Kolmogorov-Smirnov test. Between-group comparisons (sex, metabolic phenotype) will employ unpaired t-tests or Mann-Whitney U tests; comparisons across obesity categories will use ANOVA. Longitudinal changes following surgery will be evaluated with repeated measures ANOVA or paired t-tests. Correlations will be analyzed using Pearson or Spearman methods, and logistic regression models will be developed to identify predictive factors for specific metabolic responses.
This study aims to determine whether gut microbiota alterations are directly linked to metabolic abnormalities across obesity phenotypes and whether bariatric surgery elicits differential microbial and hormonal responses according to degree of adiposity and sex. It further explores whether gastrointestinal peptides and other peripheral biomarkers can refine obesity phenotyping and enhance individualized clinical management.
- Conditions
- Obese Patients With Bariatric Surgery
- Being tested
- Bariatric surgery
- Keywords
- obesity, gut microbiota, metabolic syndrome
- Medical subject headings
- Obesity, Metabolic Syndrome
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Bariatric surgeryProcedure or surgery
Also called Roux en-Y bypass, sleeve gastrectomy, Single anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S)
Bariatric surgery according to surgeon's assessment.
| Study group | Role | What they receive |
|---|---|---|
| Bariatric surgery in patients with obesity | Experimental | Patients will undergo bariatric surgery if they meet the inclusion criteria and are willing to participate in the study. Receives: Procedure: Bariatric surgery |
What is being measured
The primary outcome is the main question the study is designed to answer.
Analyze the changes in the diversity of the intestinal microbiota after bariatric surgery.
To assess the alpha-diversity of the intestinal microbiota, defined as the average diversity of species in an ecosystem, the Shannon index will be used. The results are interpreted as follows: values less than 2 are considered low in diversity and values greater than 3 are high in species diversity.
Measured: 5 years
Assess differences in the diversity of the intestinal microbiota after bariatric surgery depending on the surgical procedure (Roux-en-Y gastric bypass vs sleeve gastrectomy vs SADI-S).
To assess the beta-diversity of the intestinal microbiota, defined as the average diversity of species in an ecosystem, the Bray-Curtis index will be used. The results are interpreted as follows: values less than 2 are considered low in diversity and values greater than 3 are high in species diversity.
Measured: 5 years
Secondary outcomes (25)
Evaluate the differences in the diversity of the intestinal microbiota depending on whether patients present metabolically healthy obesity (MHO) or metabolically unhealthy obesity (MUHO) before surgery
To asses the differences in alpha-diversity of the intestinal microbiota in both groups, it will be evaluated whether there are significant differences between the Shannon indices of the two groups. The classification of patients between MHO and MUHO will be carried out using the following criteria: MUHO will be considered when patients with obesity present ≥2 metabolic abnormalities, and MHO with ≤1 metabolic abnormalities; the following cardiovascular risk factors are considered metabolic abnormalities: elevated blood pressure (defined as either SBP ≥130 mm Hg, DBP ≥85 mm Hg, or treatment with antihypertensive medications), elevated triglycerides (as fasting triglyceride concentration ≥1.7 mmol/l), low HDL-C levels (defined as HDL-C <1.04 mmol/l, in men, <1.29 mmol/l/l in women, or treatment with lipid-lowering medications), dysglycemia (fasting plasma glucose 5.6 to 6.9 mmol/l, and/or and insulin resistance as HOMA-IR >3.8).
Measured: 5 years
Evaluate significant changes in body fat mass percentage after bariatric surgery.
Percentage of body fat mass will be measured by bioelectrical impedance. It is considered to be high when ≥25% in men and ≥30% in women. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess significant changes in high-sensitivity C-reactive protein (hs-CRP) as an inflammatory parameter after bariatric surgery.
Participants will be considered to have achieved an improvement in high-sensitivity C-reactive protein levels if they normalize its value (normality values defined between 0 and 1.69mg/dl).
Measured: 3 years
Evaluate significant changes in C3 protein as an inflammatory parameter after bariatric surgery.
Participants will be considered to have achieved an improvement in C3 protein if they normalize its value (normality values defined between 81 and 157mg/dl).
Measured: 3 years
Evaluate significant changes in interleukin 1-beta (IL-1B) levels as a pro-inflammatory molecule after bariatric surgery.
IL-1B levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Evaluate significant changes in interleukin 6 (IL-6) levels as a pro-inflammatory molecule after bariatric surgery.
IL-6 levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Evaluate significant changes in tumor necrosis factor alpha (TNF-alpha) levels as a pro-inflammatory molecule after bariatric surgery.
TNF-alpha levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess significant changes in superoxide dismutase (SOD) levels after bariatric surgery.
Superoxide dismutase levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Analyze the significant differences between metabolomic profile before and after bariatric surgery, and between different surgery procedures (Roux-en-Y gastric bypass vs. sleeve gastrectomy).
NMR spectra will be used to obtain spectra from serum samples from the cohort. In order to evaluate if there will be significant differences after the dietetic intervention, a PLS-DA model for discrimination between basal and post intervention levels will be performed. Scores plots will be calculated with a 95% confidence interval.
Measured: 3 years
Evaluate if there is a significant reduction after bariatric surgery in total ROS levels.
Total ROS levels will be assessed by a flow cytometry assay. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess if there is a significant reduction after bariatric surgery in glutathione levels.
Total glutathione levels will be assessed by a flow cytometry assay. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Analyze if there is a significant change after bariatric surgery in total free radicals levels.
Total free radicals will be assessed by a flow cytometry assay. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Analyze if there is a significant reduction after bariatric surgery in mitochondrial ROS production.
Mitochondrial ROS production will be assessed by a flow cytometry assay. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Evaluate if there is a significant change after bariatric surgery in superoxide levels.
Superoxide content will be assessed by a flow cytometry assay. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Evaluate if there is a significant improvement after bariatric surgery in mitochondrial membrane potential.
Mitochondrial membrane potential will be assessed by a flow cytometry assay. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Identify and assess the differences in metabolic pathways of gut microbiota after bariatric surgery.
Genetic markers of inflammation and metabolic pathways will be analyzed from the faeces samples, in order to identify different clusters of these pathways and determine the potential functions of gut microbiota. For that purpose, transcriptome will be quantified with nanostring techology. The relative quantity of gene expression (fold change) of each gene will be calculated with the comparative 2-ΔΔCT method, and significant differences will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 5 years
Analyze if there is a significant reduction after the bariatric surgery in adipsin levels.
Adipsin levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess significant changes in plasmatic resistin levels as an inflammatory parameter after surgical intervention.
Resistin levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Analyze if there is a significant change after the bariatric surgery in leptin levels.
Leptin will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Evaluate significant reductions in Plasminogen activator inhibitor-1 (PAI-1) as an inflammatory parameter after the bariatric surgery.
PAI-1 levels will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess if there is a significant change after the bariatric surgery in ghrelin levels.
Ghrelin will be measured using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess significant changes in serum Glucagon-like peptide-1 (GLP-1) levels after the bariatric surgery.
GLP-1 levels will be assessed using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Assess if there is a significant improvement after bariatric surgery in peptide YY (PYY) levels.
PYY levels will be assessed using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Evaluate significant changes in serum gastric inhibitory polypeptide (GIP) levels after the bariatric surgery.
GIP levels will be assessed using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Analyze if there is a significant improvement after bariatric surgery in cholecystokinin (CCK) levels.
CCK levels will be assessed using the Luminex® 200 analyzer system. A significant improvement will be considered when notable differences are observed in the mean values between groups measured through p-value (<0.05) with a 95% confidence interval.
Measured: 3 years
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted11 Dec 2025
- Study start3 Mar 2021
- Primary completion31 Jan 2025
- Study completion31 May 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (12)Papers the sponsor has linked to this study.
- Other trials for Obese Patients With Bariatric SurgeryStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Enrolment
- 60 participants (actual)
Sponsor and investigators
- Lead sponsor
- Celia Bañuls
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor-investigator, Celia Bañuls, Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07277465
- Sponsor's protocol ID
- CEIm: 8/21
- Acronym
- MICROOBAR
- Status last verified
- Dec 2025
- First submitted
- 30 Nov 2025
- Last updated
- 18 Dec 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Publications
Nijhawan S, Richards W, O'Hea MF, Audia JP, Alvarez DF. Bariatric surgery rapidly improves mitochondrial respiration in morbidly obese patients. Surg Endosc. 2013 Dec;27(12):4569-73. doi: 10.1007/s00464-013-3125-y. Epub 2013 Aug 24.
PubMed 23982645Akalestou E, Miras AD, Rutter GA, le Roux CW. Mechanisms of Weight Loss After Obesity Surgery. Endocr Rev. 2022 Jan 12;43(1):19-34. doi: 10.1210/endrev/bnab022.
PubMed 34363458Ciobarca D, Catoi AF, Copaescu C, Miere D, Crisan G. Bariatric Surgery in Obesity: Effects on Gut Microbiota and Micronutrient Status. Nutrients. 2020 Jan 16;12(1):235. doi: 10.3390/nu12010235.
PubMed 31963247Cani PD, Van Hul M, Lefort C, Depommier C, Rastelli M, Everard A. Microbial regulation of organismal energy homeostasis. Nat Metab. 2019 Jan;1(1):34-46. doi: 10.1038/s42255-018-0017-4. Epub 2019 Jan 7.
PubMed 32694818Aron-Wisnewsky J, Prifti E, Belda E, Ichou F, Kayser BD, Dao MC, Verger EO, Hedjazi L, Bouillot JL, Chevallier JM, Pons N, Le Chatelier E, Levenez F, Ehrlich SD, Dore J, Zucker JD, Clement K. Major microbiota dysbiosis in severe obesity: fate after bariatric surgery. Gut. 2019 Jan;68(1):70-82. doi: 10.1136/gutjnl-2018-316103. Epub 2018 Jun 13.
PubMed 29899081Kootte RS, Levin E, Salojarvi J, Smits LP, Hartstra AV, Udayappan SD, Hermes G, Bouter KE, Koopen AM, Holst JJ, Knop FK, Blaak EE, Zhao J, Smidt H, Harms AC, Hankemeijer T, Bergman JJGHM, Romijn HA, Schaap FG, Olde Damink SWM, Ackermans MT, Dallinga-Thie GM, Zoetendal E, de Vos WM, Serlie MJ, Stroes ESG, Groen AK, Nieuwdorp M. Improvement of Insulin Sensitivity after Lean Donor Feces in Metabolic Syndrome Is Driven by Baseline Intestinal Microbiota Composition. Cell Metab. 2017 Oct 3;26(4):611-619.e6. doi: 10.1016/j.cmet.2017.09.008.
PubMed 28978426Sroka-Oleksiak A, Mlodzinska A, Bulanda M, Salamon D, Major P, Stanek M, Gosiewski T. Metagenomic Analysis of Duodenal Microbiota Reveals a Potential Biomarker of Dysbiosis in the Course of Obesity and Type 2 Diabetes: A Pilot Study. J Clin Med. 2020 Jan 29;9(2):369. doi: 10.3390/jcm9020369.
PubMed 32013181Amabebe E, Robert FO, Agbalalah T, Orubu ESF. Microbial dysbiosis-induced obesity: role of gut microbiota in homoeostasis of energy metabolism. Br J Nutr. 2020 May 28;123(10):1127-1137. doi: 10.1017/S0007114520000380. Epub 2020 Feb 3.
PubMed 32008579Bouter KE, van Raalte DH, Groen AK, Nieuwdorp M. Role of the Gut Microbiome in the Pathogenesis of Obesity and Obesity-Related Metabolic Dysfunction. Gastroenterology. 2017 May;152(7):1671-1678. doi: 10.1053/j.gastro.2016.12.048. Epub 2017 Feb 10.
PubMed 28192102Haluzik M, Kratochvilova H, Haluzikova D, Mraz M. Gut as an emerging organ for the treatment of diabetes: focus on mechanism of action of bariatric and endoscopic interventions. J Endocrinol. 2018 Apr;237(1):R1-R17. doi: 10.1530/JOE-17-0438. Epub 2018 Jan 29.
PubMed 29378901Murphy R, Clarke MG, Evennett NJ, John Robinson S, Lee Humphreys M, Hammodat H, Jones B, Kim DD, Cutfield R, Johnson MH, Plank LD, Booth MWC. Laparoscopic Sleeve Gastrectomy Versus Banded Roux-en-Y Gastric Bypass for Diabetes and Obesity: a Prospective Randomised Double-Blind Trial. Obes Surg. 2018 Feb;28(2):293-302. doi: 10.1007/s11695-017-2872-6.
PubMed 28840525Pareek M, Schauer PR, Kaplan LM, Leiter LA, Rubino F, Bhatt DL. Metabolic Surgery: Weight Loss, Diabetes, and Beyond. J Am Coll Cardiol. 2018 Feb 13;71(6):670-687. doi: 10.1016/j.jacc.2017.12.014.
PubMed 29420964
Study at a glance
From the registry record, last updated by the sponsor on 18 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Role of the Microbiota in Obesity: Effect After Bariatric Surgery
- ClinicalTrials.gov ID
- NCT07277465
- Acronym / sponsor ID
- MICROOBAR / CEIm: 8/21
- Conditions
- Obese Patients With Bariatric Surgery
- Keywords
- obesity, gut microbiota, metabolic syndrome
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 60 participants (actual)
- Lead sponsor
- Celia BañulsUniversity, hospital or other
- Study start
- 3 Mar 2021 (actual)
- Primary completion
- 31 Jan 2025 (actual)
- Study completion
- 31 May 2025 (actual)
- First posted
- 11 Dec 2025 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
Several studies have demonstrated that bariatric surgery is effective for inducing weight loss in obese patients. In addition, the effects of this surgery on multiple associated alterations are well known, including changes in the secretion and activity of hormones involved in appetite regulation, satiety, and energy expenditure, as well as alterations in the gut microbiota composition.
However, in cases of severe obesity, recent data have challenged the prevailing view, as bacterial species associated with low microbial richness (prior to surgery) appear to change only marginally after bariatric surgery, despite significant metabolic improvements.
Our objective is to examine whether gut microbiota and gastrointestinal peptides are further impaired in severe obesity and, additionally, to explore how the microbiota relates to metabolic profile or sex, as well as whether bariatric surgery may differentially correct obesity-related intestinal microbial features.
To this end, we propose a prospective, interventional, translational clinical study involving a cohort of 60 obese patients (BMI > 35 kg/m²) undergoing laparoscopic gastric bypass surgery. Patients will be grouped according to their degree of obesity to assess potential baseline differences and to evaluate the efficacy of the intervention. Furthermore, we will investigate whether these parameters differ according to metabolic profile or sex.
Body composition and nutritional status will be assessed, along with cardiovascular risk factors and comorbidities (hypertension, obstructive sleep apnea syndrome, dyslipidemia, type 2 diabetes mellitus, and insulin resistance). Gastrointestinal hormones (ghrelin, GIP, GLP-1, PYY, CCK, and leptin) will be measured in serum using Luminex XMAP technology. The content and diversity of the gut microbiota will be analyzed (16S rRNA amplicon sequencing and shotgun metagenomic sequencing using Illumina MiSeq technology) in stool samples collected before and 6-12 months after surgery. Additionally, individualized dietary follow-up and assessment of participants' quality of life will be conducted.
Detailed description
Obesity and type 2 diabetes mellitus (T2DM) continue to increase worldwide and are strongly associated with adverse metabolic and cardiovascular outcomes. Bariatric surgery, particularly laparoscopic gastric bypass (LGB), remains the most effective therapeutic strategy for substantial weight reduction, glycemic improvement, and favorable modulation of gastrointestinal hormones, bile acids, and gut microbiota. Nevertheless, the mechanisms explaining heterogeneous metabolic responses-especially in individuals with severe, morbid, or extreme obesity-remain insufficiently elucidated. In particular, gut microbial diversity, microbial gene richness, and related inflammatory pathways appear to contribute to metabolic health, yet their behavior in severe obesity and their evolution following bariatric surgery remain poorly characterized.
To address these gaps, the investigators designed a prospective, interventional, comparative, and translational clinical study including 60 obese individuals scheduled for bariatric surgery at a single tertiary hospital. Participants will be consecutively recruited according to strict inclusion and exclusion criteria and classified by degree of adiposity (severe, morbid, or extreme obesity), metabolic phenotype (metabolically healthy or metabolically abnormal obesity), and sex.
Prior to the surgical intervention, a structured dietary protocol will be implemented. Participants will receive an individualized hypocaloric diet tailored to nutritional requirements, with a macronutrient distribution of 55% carbohydrates, 30% fats, and 15% proteins. During the two weeks preceding surgery, a very low-calorie diet based on Optisource® sachets will be administered in three daily intakes. Postoperative dietary progression will follow standardized clinical guidelines, with close monitoring to support weight reduction and metabolic stabilization. Follow-up evaluations will occur at 1, 6, and 12 months after surgery.
All participants will undergo comprehensive baseline and longitudinal assessments, including: evaluation of nutritional status; anthropometric measurements; body composition and basal metabolism; cardiovascular risk factors; metabolic comorbidities; and exclusion of secondary causes of obesity. Analytical parameters will include fasting plasma glucose, lipid profile (triglycerides, HDL-cholesterol), blood pressure, markers of hepatic and renal function, and additional biochemical indices relevant to obesity and T2DM risk stratification. Gut microbiota profiling will be conducted to evaluate microbial composition, diversity, and gene richness. Gastrointestinal hormone analyses will quantify circulating incretins and appetite-regulating peptides, including GLP-1, PYY, and ghrelin, to explore their association with postoperative metabolic outcomes. Oxidative stress and inflammatory parameters will be also assessed in order to stratify cardiovascular risk before and after induced weight loss after bariatric surgery.
Statistical analyses will be performed using SPSS 17.0. Categorical variables will be summarized with frequency distributions and percentages. Quantitative variables will be described using mean, range, and standard deviation, with normality assessed via the Kolmogorov-Smirnov test. Between-group comparisons (sex, metabolic phenotype) will employ unpaired t-tests or Mann-Whitney U tests; comparisons across obesity categories will use ANOVA. Longitudinal changes following surgery will be evaluated with repeated measures ANOVA or paired t-tests. Correlations will be analyzed using Pearson or Spearman methods, and logistic regression models will be developed to identify predictive factors for specific metabolic responses.
This study aims to determine whether gut microbiota alterations are directly linked to metabolic abnormalities across obesity phenotypes and whether bariatric surgery elicits differential microbial and hormonal responses according to degree of adiposity and sex. It further explores whether gastrointestinal peptides and other peripheral biomarkers can refine obesity phenotyping and enhance individualized clinical management.
Study design
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Bariatric surgery in patients with obesity | Experimental | Procedure: Bariatric surgeryPatients will undergo bariatric surgery if they meet the inclusion criteria and are willing to participate in the study. |
Who may qualify
- Ages
- 18 to 65 years
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (3 listed)
- Patients with a body mass index (BMI) greater than 40 kg/m² (or > 35 kg/m² with minimum one obesity comorbidity).
- Aged between 18 and 65 years.
- Patients with a known duration of obesity exceeding five years, despite dietary interventions and farmacological treatment.
Key exclusion criteria (1 listed)
- Due to the nature of the study, patients with acute or chronic inflammatory diseases, established hepatic or renal insufficiency (defined as transaminase levels ±2 SD from the mean and estimated glomerular filtration rate [CKD-EPI formula] >60), neoplasic diseases, or secondary causes of obesity (e.g., hypothyroidism, Cushing's syndrome) will be excluded.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Bariatric surgeryAlso: Roux en-Y bypass, sleeve gastrectomy, Single anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S)Bariatric surgery according to surgeon's assessment. | Procedure or surgery | Bariatric surgery in patients with obesity |
Primary outcome
Analyze the changes in the diversity of the intestinal microbiota after bariatric surgery.
Time frame: 5 years
To assess the alpha-diversity of the intestinal microbiota, defined as the average diversity of species in an ecosystem, the Shannon index will be used. The results are interpreted as follows: values less than 2 are considered low in diversity and values greater than 3 are high in species diversity.
Assess differences in the diversity of the intestinal microbiota after bariatric surgery depending on the surgical procedure (Roux-en-Y gastric bypass vs sleeve gastrectomy vs SADI-S).
Time frame: 5 years
To assess the beta-diversity of the intestinal microbiota, defined as the average diversity of species in an ecosystem, the Bray-Curtis index will be used. The results are interpreted as follows: values less than 2 are considered low in diversity and values greater than 3 are high in species diversity.
25 secondary outcomes
Evaluate the differences in the diversity of the intestinal microbiota depending on whether patients present metabolically healthy obesity (MHO) or metabolically unhealthy obesity (MUHO) before surgery
Time frame: 5 years
Evaluate significant changes in body fat mass percentage after bariatric surgery.
Time frame: 3 years
Assess significant changes in high-sensitivity C-reactive protein (hs-CRP) as an inflammatory parameter after bariatric surgery.
Time frame: 3 years
Evaluate significant changes in C3 protein as an inflammatory parameter after bariatric surgery.
Time frame: 3 years
Evaluate significant changes in interleukin 1-beta (IL-1B) levels as a pro-inflammatory molecule after bariatric surgery.
Time frame: 3 years
Evaluate significant changes in interleukin 6 (IL-6) levels as a pro-inflammatory molecule after bariatric surgery.
Time frame: 3 years
Evaluate significant changes in tumor necrosis factor alpha (TNF-alpha) levels as a pro-inflammatory molecule after bariatric surgery.
Time frame: 3 years
Assess significant changes in superoxide dismutase (SOD) levels after bariatric surgery.
Time frame: 3 years
Analyze the significant differences between metabolomic profile before and after bariatric surgery, and between different surgery procedures (Roux-en-Y gastric bypass vs. sleeve gastrectomy).
Time frame: 3 years
Evaluate if there is a significant reduction after bariatric surgery in total ROS levels.
Time frame: 3 years
Assess if there is a significant reduction after bariatric surgery in glutathione levels.
Time frame: 3 years
Analyze if there is a significant change after bariatric surgery in total free radicals levels.
Time frame: 3 years
Analyze if there is a significant reduction after bariatric surgery in mitochondrial ROS production.
Time frame: 3 years
Evaluate if there is a significant change after bariatric surgery in superoxide levels.
Time frame: 3 years
Evaluate if there is a significant improvement after bariatric surgery in mitochondrial membrane potential.
Time frame: 3 years
Identify and assess the differences in metabolic pathways of gut microbiota after bariatric surgery.
Time frame: 5 years
Analyze if there is a significant reduction after the bariatric surgery in adipsin levels.
Time frame: 3 years
Assess significant changes in plasmatic resistin levels as an inflammatory parameter after surgical intervention.
Time frame: 3 years
Analyze if there is a significant change after the bariatric surgery in leptin levels.
Time frame: 3 years
Evaluate significant reductions in Plasminogen activator inhibitor-1 (PAI-1) as an inflammatory parameter after the bariatric surgery.
Time frame: 3 years
Assess if there is a significant change after the bariatric surgery in ghrelin levels.
Time frame: 3 years
Assess significant changes in serum Glucagon-like peptide-1 (GLP-1) levels after the bariatric surgery.
Time frame: 3 years
Assess if there is a significant improvement after bariatric surgery in peptide YY (PYY) levels.
Time frame: 3 years
Evaluate significant changes in serum gastric inhibitory polypeptide (GIP) levels after the bariatric surgery.
Time frame: 3 years
Analyze if there is a significant improvement after bariatric surgery in cholecystokinin (CCK) levels.
Time frame: 3 years
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 18 Dec 2025.
- Background: PubMed 23982645Nijhawan S, Richards W, O'Hea MF, Audia JP, Alvarez DF. Bariatric surgery rapidly improves mitochondrial respiration in morbidly obese patients. Surg Endosc. 2013 Dec;27(12):4569-73. doi: 10.1007/s00464-013-3125-y. Epub 2013 Aug 24.
- Background: PubMed 34363458Akalestou E, Miras AD, Rutter GA, le Roux CW. Mechanisms of Weight Loss After Obesity Surgery. Endocr Rev. 2022 Jan 12;43(1):19-34. doi: 10.1210/endrev/bnab022.
- Background: PubMed 31963247Ciobarca D, Catoi AF, Copaescu C, Miere D, Crisan G. Bariatric Surgery in Obesity: Effects on Gut Microbiota and Micronutrient Status. Nutrients. 2020 Jan 16;12(1):235. doi: 10.3390/nu12010235.
- Background: PubMed 32694818Cani PD, Van Hul M, Lefort C, Depommier C, Rastelli M, Everard A. Microbial regulation of organismal energy homeostasis. Nat Metab. 2019 Jan;1(1):34-46. doi: 10.1038/s42255-018-0017-4. Epub 2019 Jan 7.
- Background: PubMed 29899081Aron-Wisnewsky J, Prifti E, Belda E, Ichou F, Kayser BD, Dao MC, Verger EO, Hedjazi L, Bouillot JL, Chevallier JM, Pons N, Le Chatelier E, Levenez F, Ehrlich SD, Dore J, Zucker JD, Clement K. Major microbiota dysbiosis in severe obesity: fate after bariatric surgery. Gut. 2019 Jan;68(1):70-82. doi: 10.1136/gutjnl-2018-316103. Epub 2018 Jun 13.
- Background: PubMed 28978426Kootte RS, Levin E, Salojarvi J, Smits LP, Hartstra AV, Udayappan SD, Hermes G, Bouter KE, Koopen AM, Holst JJ, Knop FK, Blaak EE, Zhao J, Smidt H, Harms AC, Hankemeijer T, Bergman JJGHM, Romijn HA, Schaap FG, Olde Damink SWM, Ackermans MT, Dallinga-Thie GM, Zoetendal E, de Vos WM, Serlie MJ, Stroes ESG, Groen AK, Nieuwdorp M. Improvement of Insulin Sensitivity after Lean Donor Feces in Metabolic Syndrome Is Driven by Baseline Intestinal Microbiota Composition. Cell Metab. 2017 Oct 3;26(4):611-619.e6. doi: 10.1016/j.cmet.2017.09.008.
- Background: PubMed 32013181Sroka-Oleksiak A, Mlodzinska A, Bulanda M, Salamon D, Major P, Stanek M, Gosiewski T. Metagenomic Analysis of Duodenal Microbiota Reveals a Potential Biomarker of Dysbiosis in the Course of Obesity and Type 2 Diabetes: A Pilot Study. J Clin Med. 2020 Jan 29;9(2):369. doi: 10.3390/jcm9020369.
- Background: PubMed 32008579Amabebe E, Robert FO, Agbalalah T, Orubu ESF. Microbial dysbiosis-induced obesity: role of gut microbiota in homoeostasis of energy metabolism. Br J Nutr. 2020 May 28;123(10):1127-1137. doi: 10.1017/S0007114520000380. Epub 2020 Feb 3.
- Background: PubMed 28192102Bouter KE, van Raalte DH, Groen AK, Nieuwdorp M. Role of the Gut Microbiome in the Pathogenesis of Obesity and Obesity-Related Metabolic Dysfunction. Gastroenterology. 2017 May;152(7):1671-1678. doi: 10.1053/j.gastro.2016.12.048. Epub 2017 Feb 10.
- Background: PubMed 29378901Haluzik M, Kratochvilova H, Haluzikova D, Mraz M. Gut as an emerging organ for the treatment of diabetes: focus on mechanism of action of bariatric and endoscopic interventions. J Endocrinol. 2018 Apr;237(1):R1-R17. doi: 10.1530/JOE-17-0438. Epub 2018 Jan 29.
- Background: PubMed 28840525Murphy R, Clarke MG, Evennett NJ, John Robinson S, Lee Humphreys M, Hammodat H, Jones B, Kim DD, Cutfield R, Johnson MH, Plank LD, Booth MWC. Laparoscopic Sleeve Gastrectomy Versus Banded Roux-en-Y Gastric Bypass for Diabetes and Obesity: a Prospective Randomised Double-Blind Trial. Obes Surg. 2018 Feb;28(2):293-302. doi: 10.1007/s11695-017-2872-6.
- Background: PubMed 29420964Pareek M, Schauer PR, Kaplan LM, Leiter LA, Rubino F, Bhatt DL. Metabolic Surgery: Weight Loss, Diabetes, and Beyond. J Am Coll Cardiol. 2018 Feb 13;71(6):670-687. doi: 10.1016/j.jacc.2017.12.014.
- Individual participant dataSharing planned: No
Related trials for Obese Patients With Bariatric Surgery
RecruitingObservational study
Bariatric Surgery and Gut Microbiota Changes Over Time
Obese Patients, Obese Patients With Bariatric Surgery
RecruitingObservational study
Blood Collection Biorepository for Liver Disease Research
Non-Alcoholic Steatohepatitis(NASH), Hepatitis C
Not yet recruitingPhase 4
Semaglutide Before Primary Metabolic and Bariatric Surgery in Patients With BMI 60 kg/m² or Higher
Morbid Obesity
Recruiting
Get-Ready App to Monitoring Obesity Patients Before and After Bariatric Surgery
Obesity
Active, not recruiting
The PREBA Study: Effect of Preoperative Weight Loss With a 14-day Low-calorie Diet on Surgical Procedure and Outcomes in Patients Undergoing RYGB Surgery
Bariatric Surgery, Morbid Obesity
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Bariatric surgery in people with Obese Patients With Bariatric Surgery, run by Celia Bañuls at 1 site in Spain.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 3 inclusion and 1 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 18 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Spain. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Analyze the changes in the diversity of the intestinal microbiota after bariatric surgery. (time frame: 5 years). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07277465, which also lists 12 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 18 Dec 2025.