A low FODMAP diet is associated with changes in the microbiota and reduction in breath hydrogen but not colonic volume in healthy subjects

Background & Aims: Ingestion of poorly digested, fermentable carbohydrates (FODMAPs) have been implicated in exacerbating intestinal symptoms and the reduction of intake with symptom alleviation. Restricting FODMAP intake is believed to relieve colonic distension by reducing colonic fermentation but this has not been previously directly assessed. We aimed to investigate the effect of a low FODMAP diet on colonic contents, metabolites and microbiota.Methods: A parallel randomised controlled trial in healthy adults (n=37). All subjects followed the low FODMAP diet for a week and supplemented their diet with either maltodextrin or oligofructose. Fasted assessments performed pre- and post-diet included MRI to assess colonic volume, breath testing for hydrogen and methane, and stool collection for microbiota analysis.Results: The low FODMAP diet was associated with a reduction in Bifidobacterium and breath hydrogen, which was reversed by oligofructose supplementation. Colonic volume increased in both groups, more in OF group, but the differences were not significant. Colonic volumes correlated with total breath hydrogen + methane. A divergence in Clostridiales abundance was observed with increased abundance of Ruminococcaceae on maltodextrin, while on oligofructose, Lachnospiraceae decreased. Subjects in either group with high methane production also tended to have high microbial diversity, high colonic volume and greater abundance of methanogens.Conclusion: A low FODMAP diet reduces total bacterial count and gas production with surprisingly little effect on colonic volume.