An interventional study of Low-FODMAP Diet and Gluten-Free and Lactose-Free Diet in Irritable Bowel Syndrome, sponsored by Istanbul Gelisim University. Completed at 1 site in Turkey (Türkiye). Open to participants aged 18 Years to 64 Years. Per ClinicalTrials.gov, last updated 2026-08-20.
Sponsored by Istanbul Gelisim University · Not applicable, Interventional, and Treatment
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.
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.
Exclusion Criteria:
Participants followed a low-FODMAP diet for six weeks. The intervention restricted foods high in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. Dietary adherence was monitored by telephone during the intervention.
Behavioral: Low-FODMAP Diet
Participants followed a combined gluten-free and lactose-free diet for six weeks. The intervention excluded foods containing gluten and lactose. Dietary adherence was monitored by telephone during the intervention.
Behavioral: Gluten-Free and Lactose-Free Diet
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.
Also known as: Low Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols Diet
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.
Also known as: Combined Gluten-Free and Lactose-Free Diet
Change From Baseline in Irritable Bowel Syndrome Symptom Severity Score at 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.
Time frame: Baseline and Week 6
Change From Baseline in Abdominal Pain Severity at 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.
Time frame: Baseline and Week 6
Change From Baseline in Abdominal Pain Frequency at 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.
Time frame: Baseline and Week 6
Change From Baseline in Abdominal Bloating Severity at 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.
Time frame: Baseline and Week 6
Change From Baseline in Dissatisfaction With Bowel Habits at 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.
Time frame: Baseline and Week 6
Change From Baseline in Interference of Bowel Symptoms With Daily Life at 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.
Time frame: Baseline and Week 6
Plan to share: No — Individual participant data will not be shared because the informed consent process did not include a specific provision for sharing participant-level data with external researchers.
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Istanbul Gelisim University