Dietary Interventions for Irritable Bowel Syndrome

Overview

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.