The Gut–Brain–Muscle Axis: Microbial Regulation of Neuromuscular Aging and Cognitive Frailty

Cognitive frailty, characterized by the coexistence of physical frailty and cognitive impairment, has emerged as a major challenge in aging populations and is closely linked to sarcopenia, neurodegeneration, and chronic inflammation. Increasing evidence suggests that the gut microbiota acts as a central regulator of neuromuscular and neurocognitive aging through the integrated gut–brain–muscle axis. This review highlights how microbial dysbiosis, reduced short-chain fatty acid (SCFA) production, systemic endotoxemia, and altered microbial metabolites contribute to mitochondrial dysfunction, neuroinflammation, anabolic resistance, and impaired neuroplasticity. Key signaling mediators, including SCFAs, bile acids, tryptophan-derived metabolites, cytokines, and myokines such as irisin, brain-derived neurotrophic factor (BDNF), and cathepsin B, orchestrate bidirectional communication among the gut, skeletal muscle, and brain. We further discuss the role of exercise-induced microbiota remodeling and muscle endocrine signaling in promoting mitochondrial biogenesis and cognitive resilience. In addition, emerging translational strategies including probiotics, prebiotics, postbiotics, polyphenol-rich functional foods, marine bioactives, and precision nutrition are explored as potential interventions targeting this axis. Collectively, the gut–brain–muscle axis provides a novel systems biology framework for understanding cognitive frailty and developing integrated therapeutic strategies for healthy longevity.