Abstract Background The intestinal microbiota plays a critical role in the pathogenesis of Inflammatory Bowel Disease (IBD), with reduction in diversity and specific taxonomic shifts observed in patients compared to healthy controls. Diet is a key modifiable factor in modulating the microbiome and is increasingly being utilised as a therapeutic strategy. We aimed to review the impact of diet interventions on the gastrointestinal microbiome in patients with IBD. Methods A systematic search of MEDLINE, EMBASE, Cochrane and CINAHL was conducted up to October 2025. Studies were included if they reported on dietary intake, which provided nutritional value, in patients with IBD and reported on microbiological outcomes. Results 45 studies were included, encompassing Exclusive Enteral Nutrition (EEN), Mediterranean Diet, low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP), high fibre, as well as habitual diet. Literature supports the impact of EEN in reducing inflammation, however this was associated with depletion of short chain fatty acid producing bacteria, including Faecalibacterium and Roseburia. While a low FODMAP diet can improve gastrointestinal symptoms, this was similarly associated with a reduction in purportedly beneficial bacteria. In contrast, diets enriched in fibre, plant-based proteins, and unsaturated fats were associated with enrichment of taxa observed in healthy controls. Considerable heterogeneity in study design, administration of diet, microbial testing methods and disease activity limited direct comparisons. Conclusion Diet plays a critical, though complex, role in shaping the gastrointestinal microbiome in IBD. Strategies based on wholefoods consumption, with enrichment of fibre and unsaturated fats, support restoration of microbial patterns. Conflict of interest: Dr. Lee, Tanya: No conflict of interest Fehily, Sasha: No conflict of interest Trakman, Gina: No conflict of interest Russell, Erin: No conflict of interest Flanagan, Emma: Grant: Research grant from Ferring. Personal Fees: Personal fees from Abbvie, Ferring, Janssen, Sandoz, Takeda. Educational support from Pfizer. Kamm, Michael Albert: No conflict of interest Wright, Emily Kate: Speaker Fees, Consultancy and Advisory Boards: AbbVie, Celltrion, Falk, Ferring, Janssen, Pfizer. Research funding/support: AbbVie, Ferring, Janssen.
Lee et al. (Thu,) studied this question.