Diet, gut microbiota, and the gut-brain axis: mechanistic interactions and therapeutic implications in neuropsychiatric disorders.

The gut microbiota is a dynamic trans-kingdom ecosystem that contributes to host immunological, metabolic, and neuroendocrine homeostasis through the microbiota-gut-brain axis (MGBA). Diet is one of the major environmental factors shaping this axis, as it influences microbial composition, microbial production of neuroactive metabolites, and intestinal barrier integrity. Dysbiosis has been increasingly associated with neurological, psychiatric, and neurodevelopmental disorders, including Alzheimer's disease, Parkinson's disease, depression, autism spectrum disorder, and attention-deficit/hyperactivity disorder. Experimental studies have identified several potential mechanisms linking gut microbiota to brain function, including immune modulation, vagus nerve signaling, microbial metabolite production, and blood-brain barrier regulation. However, translating these findings into clinical practice remains challenging because human studies are affected by genetic heterogeneity, dietary variation, medication use, lifestyle factors, and disease-specific confounders. In this review, we summarize current evidence on the interactions among diet, gut microbiota, and brain function, with particular emphasis on microbial metabolites, immune mediators, and barrier-related mechanisms. We also critically discuss microbiota-targeted interventions, including precision nutrition, probiotics, and fecal microbiota transplantation, highlighting both their therapeutic potential and their current limitations. A more cautious and mechanistically integrated understanding of the MGBA may support the development of personalized strategies for neuropsychiatric disease prevention and management.