Clinical trial: Efficacy of a Low <scp>FODMAP</scp> Diet in Paediatric Irritable Bowel Syndrome—A Randomised Crossover Trial With Exploratory Metabolomic Analysis

BACKGROUND: Evidence supporting the low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet in paediatric irritable bowel syndrome (IBS) remains limited. Mechanisms underlying inter-individual variability in dietary response in children are poorly understood. AIM: To compare the clinical efficacy of a low FODMAP diet (LFD) versus a dietitian-guided habitual diet (HD; standard FODMAP intake) in children with IBS and to identify faecal and urinary metabolomic signatures associated with treatment response. METHODS: Single-centre, randomised assessor-blinded crossover trial. Children with Rome IV-defined IBS underwent a 2-week run-in, followed by 14 days of LFD or dietitian-guided HD, a 2-week washout, and crossover to the alternate diet. The primary outcome was treatment success (≥ 50% reduction in abdominal pain; period-specific baseline VAS). Secondary outcomes included IBS Severity Scoring System (IBS-SSS), stool pattern, and metabolomic profiling. RESULTS: Sixty-six children (mean age 10.2 years) completed the trial. Treatment success was achieved in 57.6% during LFD versus 30.3% during HD (p = 0.024), with the greatest benefit observed in children with severe baseline pain (VAS > 5). LFD was associated with significant reductions in IBS-SSS scores and bloating. Targeted SCFA analyses showed lower faecal acetic acid during LFD than during HD, while exploratory faecal and urinary volatilome analyses identified candidate features associated with response categories. CONCLUSION: In this randomised crossover trial, a LFD improved abdominal pain and symptom severity in children with IBS, with the greatest benefit in those with severe baseline pain. Exploratory faecal and urinary metabolomic analyses identified candidate features associated with non-response, warranting further validation. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT06618677.