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Completed

NCT Number: NCT07774923

Dietary Interventions for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a disorder of gut-brain interaction characterized by recurrent abdominal pain and altered bowel habits. Dietary factors may trigger or worsen symptoms such as abdominal pain, bloating, gas, diarrhea, and constipation. This study evaluated and compared the effects of a low-fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (low-FODMAP) diet and a combined gluten-free and lactose-free diet on symptom severity in adults diagnosed with IBS.

Adults aged 19-64 years with IBS followed one of the two dietary interventions for six weeks. IBS symptom severity was assessed at baseline and at the end of week 6 using the Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS). Dietary adherence was monitored by telephone during the intervention.

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Key information

Conditions

Irritable Bowel Syndrome Colonic Diseases Colonic Diseases, Functional Digestive System Diseases Gastrointestinal Diseases Intestinal Diseases

Age range

18 year–64 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Mersin University Hospital

Mersin, 33343, Turkey (Türkiye)

About this study

This interventional, parallel-group study was conducted at the Gastroenterology Outpatient Clinic of Mersin University Hospital between February 25 and July 18, 2025. The study included adults aged 19-64 years who had been diagnosed with irritable bowel syndrome, met the eligibility criteria, provided written informed consent, and agreed to follow the assigned dietary intervention.

Participants followed either a low-FODMAP diet or a combined gluten-free and lactose-free diet for six weeks. The low-FODMAP intervention restricted foods high in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. The combined gluten-free and lactose-free intervention excluded foods containing gluten and lactose. Participants received detailed dietary instructions during the initial face-to-face visit.

At baseline, a researcher administered a data collection form covering sociodemographic characteristics, health information, dietary habits, and food preparation and cooking practices. Gastrointestinal symptom severity was measured using the Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS). The IBS-SSS produces a total score ranging from 0 to 500, with higher scores indicating greater symptom severity. It assesses abdominal pain severity, frequency of abdominal pain, abdominal bloating, satisfaction with bowel habits, and the interference of bowel symptoms with daily life.

Participants were contacted by telephone one week after starting the diet and subsequently at two-week intervals to monitor adherence. At the end of the six-week intervention, the IBS-SSS was administered again during a face-to-face visit. The primary analysis evaluated the change in IBS-SSS total score from baseline to week 6 and compared symptom changes between the two dietary intervention groups.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

Adults aged 19-64 years Diagnosed with irritable bowel syndrome Male or female Provided written informed consent to participate in the study

Exclusion criteria

Pregnancy or lactation Diagnosis of cancer Presence of a gastrointestinal disease other than irritable bowel syndrome Diagnosis of diabetes mellitus Diagnosis of a psychiatric disorder

Treatment and study plan

Low-FODMAP Diet

Behavioral

Participants followed a low-FODMAP diet for six weeks. Foods high in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols were restricted. Participants received detailed dietary instructions during the initial face-to-face visit. Dietary adherence was monitored by telephone one week after starting the intervention and subsequently at two-week intervals.

Other names: Low Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols Diet

Gluten-Free and Lactose-Free Diet

Behavioral

Participants followed a combined gluten-free and lactose-free diet for six weeks. Foods containing gluten and lactose were excluded. Participants received detailed dietary instructions during the initial face-to-face visit. Dietary adherence was monitored by telephone one week after starting the intervention and subsequently at two-week intervals.

Other names: Combined Gluten-Free and Lactose-Free Diet

Primary outcomes

  1. Change From Baseline in Irritable Bowel Syndrome Symptom Severity Score at Week 6

    Time frame: Baseline and Week 6

    The Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS) was used to assess overall IBS symptom severity. The instrument includes five domains: abdominal pain severity, frequency of abdominal pain, abdominal bloating severity, satisfaction with bowel habits, and interference of bowel symptoms with daily life. The total score ranges from 0 to 500, with higher scores indicating greater symptom severity. Change was calculated as the week 6 score minus the baseline score; a negative change indicates improvement.

Secondary outcomes

  1. Change From Baseline in Abdominal Pain Severity at Week 6

    Time frame: Baseline and Week 6

    Abdominal pain severity was assessed using the corresponding IBS-SSS domain, scored from 0 to 100. Higher scores indicate greater abdominal pain severity. Change was calculated as the week 6 score minus the baseline score; a negative change indicates improvement.

  2. Change From Baseline in Abdominal Pain Frequency at Week 6

    Time frame: Baseline and Week 6

    Abdominal pain frequency was assessed using the corresponding IBS-SSS domain based on the number of days with abdominal pain during the previous 10 days. The domain score ranges from 0 to 100, with higher scores indicating more frequent abdominal pain. A negative change indicates improvement.

  3. Change From Baseline in Abdominal Bloating Severity at Week 6

    Time frame: Baseline and Week 6

    Abdominal bloating severity, including feelings of distension, fullness, and gas, was assessed using the corresponding IBS-SSS domain, scored from 0 to 100. Higher scores indicate greater symptom severity. A negative change indicates improvement.

  4. Change From Baseline in Dissatisfaction With Bowel Habits at Week 6

    Time frame: Baseline and Week 6

    Dissatisfaction with bowel habits was assessed using the corresponding IBS-SSS domain, scored from 0 to 100. Higher scores indicate greater dissatisfaction with bowel habits. A negative change indicates improvement.

  5. Change From Baseline in Interference of Bowel Symptoms With Daily Life at Week 6

    Time frame: Baseline and Week 6

    The interference of bowel symptoms with daily life was assessed using the corresponding IBS-SSS domain, scored from 0 to 100. Higher scores indicate greater interference with daily life. A negative change indicates improvement.

Sponsors and collaborators

Lead sponsor

Istanbul Gelisim University

Other

Collaborators

  • Bahçeşehir University
  • Mersin University

Registry information

Official study title

The Effects of a Low-FODMAP Diet and Gluten-Free and Lactose-Free Dietary Interventions on Symptoms in Patients Diagnosed With Irritable Bowel Syndrome

Acronym: IBS-DIET

Important dates

Study start
2025
Primary completion
2025
Study completion
2025
First posted
Aug 19, 2026
Registry last updated
Aug 19, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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