Effect of a Low FODMAP Diet in IBS and Functional Constipation with Bloating: a Randomized Double-Blind Trial
Trial statusNot yet recruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age18+
SponsorMahidol University
About this trial
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.
Eligibility criteria
This trial does not accept healthy volunteersQualifiers
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
Disqualifiers
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
Trial design
Design model
Parallel
Treatments tested in this trial
Low FODMAP Diet
Other interventionA 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.
High FODMAP Diet
Other interventionA 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.
Treatment groups
34 Participants
are divided into 2 treatment groupsGroup A: Low FODMAP DietExperimental treatment 1 intervention
Group B: High FODMAP DietActive comparator 1 intervention
Trial outcomes
Primary outcomes
1
Change in Bloating Severity (VAS)
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.
Time frame
Baseline to 2 weeks (End of Intervention)Secondary outcomes
1
Reduction in Global IBS Symptoms (IBS-SSS)
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.
Time frame
Baseline to 2 weeks2
Change in Abdominal Pain (VAS)
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.
Time frame
Baseline to 2 weeks3
Change in Stool Frequency and Consistency
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.
Time frame
Baseline to 2 weeks4
Changes in Gut Microbiota Composition
Alterations in gut microbiota diversity and abundance (16S rRNA sequencing).
Time frame
Baseline to 2 weeksLocations
Sponsors and contacts
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Source ClinicalTrials.gov
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