Background: Emerging evidence highlights the gut microbiota as a key contributor to the pathophysiology of irritable bowel syndrome (IBS), acting through complex interactions with intestinal motility, immune function, epithelial barrier integrity, and the gut-brain axis. This narrative review summarizes current knowledge regarding the roles of the gut microbiota and their metabolites in IBS. Summary: We discuss alterations in the gut microbiota in IBS, with particular emphasis on changes in short-chain fatty acid production, bile acid metabolism, serotonin signaling, and gas handling. Special attention is given to microbial metabolites as mediators of visceral hypersensitivity, intestinal permeability, and neuromodulation within the microbiota–gut–brain axis. Major alterations in the gut microbiota of IBS are characterized by a reduction in Bacteroidetes, Bifidobacteria, and Faecalibacterium, accompanied by an increase in Firmicutes. We explain the importance of butyrate metabolism in colonic epithelial cells for maintaining the anaerobic environment of the gut. In addition, we review the impact of diet-microbiota interactions, including FODMAP restriction, resistant starch intake, and protein fermentation, on symptom generation and microbial stability. Key message: Although accumulating evidence supports a link between gut dysbiosis and IBS, establishing causal relationships remains challenging due to disease heterogeneity and dietary influences. Future large-scale, well-phenotyped, multi-omics studies integrating microbiota, metabolomic, and host factors are required to elucidate underlying mechanisms and to guide personalized therapeutic strategies for IBS.
Andoh et al. (2026) studied this question.