Comparative effects of low-FODMAP and lactose-gluten-free diets on gastrointestinal symptoms and mental health in irritable bowel syndrome: a randomized crossover trial

Irritable bowel syndrome (IBS) is a prevalent condition with significant impacts on quality of life. This study aimed to evaluate whether the sequence of implementing a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) and a lactose-free, gluten-free diet influences IBS symptoms and depression–anxiety levels. Individuals with IBS were randomly assigned to either a low-FODMAP diet or a lactose-free, gluten-free diet for 4 weeks, followed by a crossover to the alternate diet for an additional 4 weeks. Gastrointestinal symptoms and psychological status were assessed using validated scales before and after each intervention period. Anthropometric and biochemical parameters were also evaluated. Both dietary interventions led to significant improvements in gastrointestinal symptoms and depression–anxiety scores over time ( P < 0.001). However, no significant differences were observed between the two diet sequences in terms of symptom severity or psychological outcomes at the end of the study ( P > 0.05). Both dietary sequences were associated with significant improvements in gastrointestinal symptoms and psychological outcomes in individuals with IBS. At the end of the study, no statistically significant differences in these outcomes were detected between the two sequences. While these findings support symptom improvement with both sequential dietary approaches, they do not establish equivalent efficacy. Further studies specifically designed to compare the relative efficacy and optimal sequencing of these dietary strategies are warranted. ClinicalTrials.gov, NCT07722572. Registered on 21 July 2026. Retrospectively registered.