Gut–brain axis in health and brain disease

The gut-brain axis is a complex, bidirectional network of communication systems that integrates neural, endocrine, and immune pathways, as well as metabolic processes, to regulate homeostasis and maintain physiological and cognitive equilibrium. Central to this axis is the gut microbiota, which exerts a profound influence on brain function through microbial metabolites, including short-chain fatty acids, tryptophan metabolites, and bile acids. Disruption of this microbial balance, known as dysbiosis, has been implicated in the onset and progression of major neuropsychiatric and neurodegenerative disorders, including depression, Alzheimer's disease, and Parkinson's disease. This review critically examines the mechanistic underpinnings of the gut-brain axis, emphasizing metabolic, immunological, and neuroendocrine signaling as key mediators. Furthermore, it explores how dietary components, particularly fiber, polyphenols, and fermented foods, modulate gut microbial composition and function to influence brain health. Emerging therapeutic strategies, such as probiotics, prebiotics, and fecal microbiota transplantation, are discussed, along with the potential of personalized targeted intervention. By integrating current findings, this review underscores the gut-brain axis as a dynamic interface that not only influences neurological and psychiatric outcomes but also represents a promising target for therapeutic intervention.