Dietary patterns, gut microbiota, and gastrointestinal disorders: mechanistic insights into irritable bowel syndrome and inflammatory bowel disease

Abstract The gut microbiota plays a central role in maintaining gastrointestinal (GI) health through its metabolic, immune-modulating, and barrier-supporting functions. Diet is among the most influential modifiable determinants shaping microbial composition and activity, thereby influencing susceptibility to GI disorders, particularly irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). This review synthesizes current evidence on the interplay between dietary patterns, gut microbiota, and the pathogenesis and management of IBS and IBD. The Mediterranean diet and plant-based dietary patterns were consistently associated with enrichment of short-chain fatty acid (SCFA)-producing taxa, including Faecalibacterium prausnitzii , Roseburia , and Bifidobacterium species, alongside enhanced intestinal barrier integrity, reduced systemic inflammation, and improved clinical outcomes in both IBS and IBD. The Low FODMAP (fermentable oligo-, di-, monosaccharides, and polyols) diet provided effective symptom relief in IBS, although its impact on microbial composition was modest and inconsistent. In contrast, the Western diet, ultra-processed foods, and the ketogenic diet were linked to dysbiosis, depletion of beneficial taxa such as Akkermansia muciniphila , increased intestinal permeability, and pro-inflammatory cytokine profiles that contributed to IBS symptomatology and IBD pathogenesis. The gut–brain axis emerged as a key mediator of bidirectional signaling between the microbiota and the central nervous system, with relevance to both gastrointestinal and psychological manifestations of IBS and IBD. In conclusion, dietary patterns substantially modulate gut microbial composition and gastrointestinal health, and the Mediterranean diet represents the most favorable pattern for both IBS and IBD. Integration of dietary counseling into clinical management, alongside long-term randomized controlled trials combining microbiome profiling with clinical endpoints, is recommended to advance personalized, microbiota-targeted nutritional strategies.