Gut Microbiota as a Key Regulator of the Gut–brain Axis and Metabolism in the Pathogenesis of Psychiatric and Metabolic Disorders: A Narrative Review

The gut microbiota has emerged as a central regulator of the gut–brain axis and systemic metabolism, playing a pivotal role in the development of both psychiatric and metabolic disorders. This review synthesizes current evidence from peer-reviewed studies indexed in PubMed to elucidate the mechanisms linking gut microbiota dysbiosis with disease pathogenesis. A structured literature review was conducted, focusing on studies published between 2004 and 2025. Evidence indicates that alterations in microbial composition and function are associated with depression, anxiety, autism spectrum disorders, obesity, type 2 diabetes, and metabolic syndrome. Mechanistically, the gut microbiota influences host physiology through neural, endocrine, immune, and metabolic pathways, including modulation of neurotransmitters, short-chain fatty acids, and inflammatory mediators. The review highlights shared biological pathways between psychiatric and metabolic disorders, emphasizing chronic inflammation and metabolic dysregulation. Emerging therapeutic strategies, including microbiota-targeted interventions such as probiotics, prebiotics, dietary modifications, and fecal microbiota transplantation, demonstrate promising clinical potential. However, heterogeneity in study designs and individual microbiome variability remain significant challenges. This review underscores the importance of integrative, multidisciplinary research and supports the gut microbiota as a novel therapeutic target.