Gut–Brain Axis and Bile Acid Signaling: Linking Microbial Metabolism to Brain Function and Metabolic Regulation

The gut-brain axis is a bidirectional communication network in which gut microbiota and their metabolites influence central nervous system (CNS) function. Among these metabolites, bile acids have emerged as key signaling molecules that modulate metabolic and neuroendocrine pathways. Microbiota-mediated modifications of bile acid composition affect receptors such as farnesoid X receptor (FXR)and Takeda G protein-coupled receptor 5 (TGR5), thereby influencing neuronal activity, appetite control, glucose metabolism, and energy balance. Emerging evidence indicates that bile acids act both directly on the CNS and indirectly via endocrine and immune mediators, linking microbial metabolism to brain function. By integrating microbiological, metabolic, and neuroendocrine perspectives, bile acids can be viewed as critical messengers in the communication between the gut microbiota and the CNS. The purpose of this review is thus to synthesize current mechanisms underlying these interactions and highlight their therapeutic potential in metabolic and neurodegenerative disorders.