Gut microbiota and brain health: Disease-specific pathways and emerging therapeutic strategies

The microbiota-gut-brain axis (MGBA) has emerged as a dynamic, bidirectional communication system linking the gastrointestinal tract and the central nervous system (CNS) through neural, immune, endocrine, and metabolic mechanisms. Increasing evidence indicates that alterations in gut microbial communities are associated with a wide range of neurological disorders; however, the strength of this association varies across diseases, and many mechanistic observations still rely predominantly on experimental models rather than human studies. This review provides an overview of current evidence regarding the role of the gut microbiota in maintaining CNS homeostasis, with particular emphasis on intestinal barrier function, immune modulation, vagal and enteric communication, and the generation of biologically active microbial metabolites, including short-chain fatty acids, bile acids, and neurotransmitter-related compounds. Studies in both clinical and experimental settings have reported disease-specific microbial signatures in conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, autism spectrum disorders, and amyotrophic lateral sclerosis. In parallel, microbiota-directed interventions-including probiotics, prebiotics, dietary approaches, fecal microbiota transplantation, and strategies targeting microbial metabolites-have produced encouraging findings in preclinical studies and early-stage clinical investigations. Nevertheless, considerable heterogeneity in study populations, experimental methodologies, and therapeutic protocols continues to limit the translation of these findings into routine clinical practice. Collectively, current evidence supports the MGBA as a valuable framework for understanding neurological diseases while underscoring the need for rigorously designed longitudinal studies and well-controlled clinical trials to define its therapeutic relevance better.