Effect of a Low FODMAP Diet in IBS and Functional Constipation with Bloating: a Randomized Double-Blind Trial

March 6, 2025 updated by: Watcharasak Chotiyaputta, Mahidol University

Effect of a Low FODMAP Diet in Irritable Bowel Syndrome and Functional Constipation with Bloating: a Randomized Double-Blind Controlled Trial with Microbiota, Intestinal Gas, and Metabolomic Analysis

This clinical study aims to evaluate the effects of a low FODMAP diet compared to a high FODMAP diet in patients with Irritable Bowel Syndrome (IBS) and Functional Constipation (FC) with predominant bloating. The study is a randomized, double-blind, controlled trial designed to assess whether a diet low in fermentable carbohydrates can improve bloating symptoms, gut microbiota composition, intestinal gas production, and metabolic outputs.

Patients meeting the Rome IV criteria for IBS or FC with persistent bloating will be enrolled and randomly assigned to receive either a low or high FODMAP diet for two weeks. Meals will be standardized to control FODMAPs composition, ensuring that FODMAP content is the primary variable.

The primary endpoint is the proportion of participants with a ≥30% reduction in bloating severity, measured using the Visual Analog Scale (VAS). Secondary outcomes include changes in global IBS symptoms, abdominal pain, bowel movements, stool consistency, microbiota diversity, hydrogen/methane gas production, and metabolomic profiles.

This study will contribute to the growing body of evidence supporting dietary management in disorders of gut-brain interaction (DGBI), particularly in bloating-predominant IBS and FC, and will provide insights into the mechanisms linking diet, gut microbiota, and symptom improvement.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Not yet recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

Irritable Bowel Syndrome (IBS) and Functional Constipation (FC) are chronic Disorders of Gut-Brain Interaction (DGBI) characterized by altered motility, visceral hypersensitivity, dysbiosis, and central nervous system processing abnormalities. Bloating is a challenging and distressing symptom that often persists despite standard pharmacological treatments.

The low FODMAP diet has been widely studied as a dietary approach to alleviate IBS symptoms. FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) are poorly absorbed short-chain carbohydrates that increase osmolarity, promote intestinal gas production, and alter gut microbiota, leading to bloating and discomfort. Although studies support the effectiveness of the low FODMAP diet, existing research lacks controlled, blinded trials assessing its impact on bloating-specific symptoms and related physiological markers.

This study addresses these gaps by using a double-blind, controlled design with rigorously standardized meals containing well-defined FODMAP content. It will assess clinical outcomes, gut microbiota composition, gas production, and metabolomic changes to elucidate the mechanisms underlying the diet's effects.

Study Design This is a randomized, double-blind, controlled trial conducted at a single center. Participants will be assigned to receive either a low FODMAP or a high FODMAP diet for two weeks.

Participants:

Adults ≥18 years diagnosed with IBS or FC with persistent bloating based on Rome IV criteria.

Intervention:

Standardized meal plans containing either low FODMAP or high FODMAP content.

Randomization:

Computer-generated block randomization (block of 4)

Blinding:

Investigators, study staff, and participants will remain blinded to the dietary allocation.

Primary Outcome:

≥30% reduction in bloating severity on the VAS scale.

Secondary Outcomes:

Changes in global IBS symptoms (IBS-SSS) or constipation symptoms (PAC-Sym) Abdominal pain (VAS) stool frequency, and consistency (Bristol Stool Form Scale). Gut microbiota diversity and composition (16S rRNA sequencing). Intestinal gas production (hydrogen/methane breath test). Metabolomic analysis (short-chain fatty acids, urine histamine, azelaic acid). Use of rescue medications for symptom relief.

Study Procedures

Baseline Assessment:

Demographic data, medical history, and dietary habits (7-day food diary). Baseline bloating severity, stool consistency, and quality of life (IBS-QoL, PAC-QoL).

Microbiota, breath test, and metabolomic sampling.

Intervention Phase (2 Weeks):

Participants consume standardized low or high FODMAP meals (3 main meals + 1 snack/day).

Daily recording of symptoms, bowel movements, and use of rescue medications.

Follow-up Assessments:

Week 1: Phone follow-up to assess adherence and symptom progression. Week 2: Final clinical and laboratory assessments (identical to baseline). Data collection for statistical analysis comparing treatment effects.

Statistical Analysis Primary endpoint (bloating reduction) analyzed using Chi-square/Fisher's exact test.

Secondary outcomes analyzed with paired t-tests, Mann-Whitney U tests, and logistic regression.

Microbiota diversity assessed using Shannon index, beta diversity, and PERMANOVA testing.

Significance and Impact This study will provide high-quality evidence on the effectiveness of the low FODMAP diet for bloating-predominant IBS and FC, addressing critical knowledge gaps. By integrating clinical, microbiota, and metabolomic data, it will enhance understanding of diet-microbiota interactions and their role in symptom modulation.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
34

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Not Applicable

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

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

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

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Age ≥18 years
  • Diagnosed with Irritable Bowel Syndrome (IBS) or Functional Constipation (FC) based on Rome IV criteria
  • Persistent bloating affecting daily life, with a bloating VAS score ≥4
  • Stable bowel habits with Bristol Stool Form Scale (BSFS) type 3-5
  • History of prior treatment with antispasmodics and/or prokinetics (allowed if dose remains stable)
  • Able to comply with dietary intervention and study procedures

Exclusion Criteria:

  • Prior gastrointestinal surgery (except appendectomy or cholecystectomy)
  • Use of antibiotics, proton pump inhibitors (PPIs), probiotics, NSAIDs, lactulose, or metformin within the past 4 weeks
  • Presence of systemic diseases affecting gut microbiota (e.g., liver cirrhosis, uncontrolled diabetes, end-stage renal disease, obesity, cancer, psychiatric disorders)
  • Inability to consume study meals or follow dietary restrictions

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

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Quadruple

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: Low FODMAP Diet
Participants will follow a low FODMAP diet for two weeks, consuming standardized meals with minimal fermentable carbohydrates. Meals match the high FODMAP diet in appearance to maintain blinding.
Other: Low FODMAP Diet
A standardized diet containing low levels of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), designed to reduce bloating and gastrointestinal symptoms. Meals are pre-prepared, calorie-matched, and visually identical to those in the high FODMAP group to maintain blinding. Participants will consume three main meals and one snack daily for two weeks, with adherence monitored through food diaries and photos.
Active Comparator: High FODMAP Diet
Participants will follow a high FODMAP diet for two weeks, consuming standardized meals with high fermentable carbohydrates. Meals match the low FODMAP diet in appearance to maintain blinding.
Other: High FODMAP Diet
A standardized diet containing high levels of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) to assess its impact on bloating and gastrointestinal symptoms. Meals are calorie-matched and visually identical to those in the low FODMAP group to maintain blinding. Participants will consume three main meals and one snack daily for two weeks, with adherence tracked through food diaries and photos.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Change in Bloating Severity (VAS)
Time Frame: Baseline to 2 weeks (End of Intervention)
The primary outcome is the change in bloating severity, measured using the Visual Analog Scale (VAS). The VAS score ranges from 0 (no bloating) to 10 (severe bloating), with higher scores indicating worse bloating symptoms. Participants will record daily bloating scores throughout the intervention period. The proportion of participants achieving a ≥30% decrease in bloating severity from baseline will be analyzed.
Baseline to 2 weeks (End of Intervention)

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Reduction in Global IBS Symptoms (IBS-SSS)
Time Frame: Baseline to 2 weeks
Change in IBS Symptom Severity Score (IBS-SSS) from baseline, assessing overall IBS symptom burden, abdominal pain, bloating, and bowel habit changes. The IBS-SSS scale ranges from 0 to 500, with higher scores indicating more severe IBS symptoms.
Baseline to 2 weeks
Change in Abdominal Pain (VAS)
Time Frame: Baseline to 2 weeks
Change in abdominal pain severity, measured using the Visual Analog Scale (VAS). The VAS scale ranges from 0 (no pain) to 10 (severe pain), with higher scores indicating worse pain severity. Participants will record daily pain scores, and the difference between baseline and post-intervention scores will be analyzed.
Baseline to 2 weeks
Change in Stool Frequency and Consistency
Time Frame: Baseline to 2 weeks

Change in bowel movement frequency and stool consistency, assessed using the Bristol Stool Form Scale (BSFS).

Stool frequency will be recorded as the number of bowel movements per day.

Stool consistency will be graded using the BSFS scale (1-7):

1-2: Hard stools (constipation) 3-4: Normal stools 5-7: Loose stools (diarrhea) Higher BSFS scores indicate looser stool consistency. The difference between baseline and post-intervention values will be analyzed.
Baseline to 2 weeks
Changes in Gut Microbiota Composition
Time Frame: Baseline to 2 weeks
Alterations in gut microbiota diversity and abundance (16S rRNA sequencing).
Baseline to 2 weeks
Change in Hydrogen Gas Production (Lactulose Breath Test)
Time Frame: Baseline to 2 weeks
Change in exhaled hydrogen (H₂) levels, measured via lactulose breath test in parts per million (ppm). Higher hydrogen levels indicate increased fermentation by colonic microbiota.
Baseline to 2 weeks
Change in Methane Gas Production (Lactulose Breath Test)
Time Frame: Baseline to 2 weeks
Change in exhaled methane (CH₄) levels, measured via lactulose breath test in parts per million (ppm). Elevated methane levels are associated with slow colonic transit and constipation.
Baseline to 2 weeks
Use of Rescue Medications
Time Frame: Baseline to 2 weeks
Frequency and dosage of antispasmodics, prokinetics, or laxatives used for symptom relief.
Baseline to 2 weeks
Change in Psychological Symptoms (DASS-21)
Time Frame: Baseline to 2 weeks

Change in Depression, Anxiety, and Stress Scores (DASS-21), a validated self-reported scale measuring psychological distress. The DASS-21 consists of three subscales:

Depression (0-21) Anxiety (0-21) Stress (0-21) Each subscale score ranges from 0 (normal) to 21 (severe symptoms), with higher scores indicating greater psychological distress. The total score is calculated by summing individual subscale scores.
Baseline to 2 weeks
Change in Quality of Life (IBS-QoL / PAC-QoL)
Time Frame: Baseline to 2 weeks

Change in IBS-specific Quality of Life (IBS-QoL) score, which assesses the impact of IBS on daily activities, emotional well-being, and social functioning.

The IBS-QoL score ranges from 0 to 100, with higher scores indicating better quality of life.
Baseline to 2 weeks
Patient Satisfaction with Treatment
Time Frame: Baseline to 2 weeks

Overall treatment satisfaction, measured using a Visual Analog Scale (VAS) ranging from 0 to 10:

0 = Completely Dissatisfied 10 = Completely Satisfied Higher scores indicate greater satisfaction with treatment. The difference between baseline and post-intervention scores will be analyzed.
Baseline to 2 weeks
Change in Patient-Reported Constipation Symptoms (PAC-SYM)
Time Frame: Baseline to 2 weeks
Change in Patient Assessment of Constipation-Symptoms (PAC-SYM) score, evaluating constipation-related symptoms, including stool consistency, discomfort, and straining. The PAC-SYM scale ranges from 0 to 48, with higher scores indicating worse constipation symptoms.
Baseline to 2 weeks
Change in Short-Chain Fatty Acids (SCFAs) Levels
Time Frame: Baseline to 2 weeks
Change in fecal short-chain fatty acids (SCFAs), including acetic acid, propionic acid, and butyric acid, measured in μmol/g stool. Higher SCFA levels indicate greater microbial fermentation activity.
Baseline to 2 weeks
Change in Urine Histamine Levels
Time Frame: Baseline to 2 weeks
Change in urine histamine concentration, measured in μg/mL urine, assessing histamine metabolism related to gut inflammation and microbiota activity. Higher levels indicate increased histamine production.
Baseline to 2 weeks
Change in Urine Azelaic Acid Levels
Time Frame: Baseline to 2 weeks
Change in urine azelaic acid concentration, measured in μg/mL urine, assessing microbial metabolic changes associated with gut dysbiosis and inflammation. Higher levels indicate altered microbial metabolism.
Baseline to 2 weeks
Change in Constipation-Specific Quality of Life (PAC-QoL)
Time Frame: Baseline to 2 weeks

Change in Patient Assessment of Constipation-Quality of Life (PAC-QoL) score, evaluating the impact of constipation on daily life, physical discomfort, psychological well-being, and social aspects.

The PAC-QoL score ranges from 0 to 100, with higher scores indicating better quality of life.
Baseline to 2 weeks

Collaborators and Investigators

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

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Mahidol University

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Study Director: Monthira Maneerattanaporn, MD, Mahidol University Faculty of Medicine Siriraj Hospital
  • Principal Investigator: Tanawat Geeratragool, MD, Mahidol University Faculty of Medicine Siriraj Hospital
  • Study Chair: Somchai Leelakusolvong, MD, Mahidol University Faculty of Medicine Siriraj Hospital

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)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
March 15, 2025

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
March 15, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
July 31, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
February 28, 2025

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
March 6, 2025

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
March 25, 2025

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
March 25, 2025

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
March 6, 2025

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
February 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • Si 148/2025

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

product manufactured in and exported from the U.S.

No

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