Food as Friend or Foe: A Decadal Narrative Review of Dietary Patterns as Determinants of Gastrointestinal Pathophysiology and Clinical Outcomes (2015–2025)

Diet is a major modifiable determinant of gastrointestinal (GI) health, influencing disease risk and progression through coordinated effects on the gut microbiome, immune regulation, epithelial barrier integrity, oxidative balance, and epigenetic mechanisms. This narrative review synthesizes epidemiological, mechanistic, and clinical evidence from the past decade to examine bidirectional relationships between dietary patterns and seven common GI disorders: celiac disease, irritable bowel syndrome (IBS), Crohn's disease, ulcerative colitis, <i>Helicobacter pylori</i>-associated gastritis, peptic ulcer disease, and lactose intolerance. Western dietary patterns, characterized by high intake of ultra-processed foods and saturated fats and low fiber consumption, are consistently associated with microbial dysbiosis, impaired barrier function, and enhanced inflammatory signaling. In contrast, Mediterranean and plant-forward dietary patterns show protective associations across multiple GI conditions. Mechanistically, diet influences GI pathophysiology largely through microbiome-derived metabolites, particularly short-chain fatty acids, which regulate epithelial homeostasis, immune tolerance, and inflammatory pathways. Condition-specific dietary strategies remain clinically important. Gluten exclusion is essential in celiac disease, low- fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) approaches provide evidence-based symptom control in IBS, and exclusive enteral nutrition or targeted exclusion diets support remission induction in Crohn's disease. Selected probiotics and emerging postbiotics may provide adjunctive benefits in specific contexts. Despite growing evidence, dietary research remains limited by methodological heterogeneity and interindividual variability. Precision nutrition approaches integrating microbiome profiling and artificial intelligence represent a promising translational direction. Overall, dietary patterns-rather than isolated nutrients-form the foundation of GI dietary therapy.