Gut Microbiota-Targeted Nutrition for Healthy Aging: Mechanistic Roles of Polyphenols and Dietary Fiber in Geroscience.

Age-related alterations in the gut microbiota contribute to chronic low-grade inflammation, immune dysregulation, metabolic dysfunction, frailty, sarcopenia, and cognitive decline. Dietary polyphenols and fermentable fiber modulate microbial composition and metabolism, promoting the production of bioactive metabolites, including short-chain fatty acids, secondary bile acids, indole derivatives, and urolithins, which regulate intestinal barrier integrity, immune homeostasis, mitochondrial function, and gut-organ communication. This narrative review critically synthesizes evidence from experimental studies, observational cohorts, randomized controlled trials, systematic reviews, and meta-analyses to examine microbiota-mediated mechanisms linking these dietary components to healthy aging within the geroscience framework. Although mechanistic evidence is compelling, translation into clinically meaningful aging outcomes remains limited because most intervention studies are small and heterogeneous and primarily rely on surrogate biomarkers. Current evidence supports polyphenol- and fiber-rich dietary patterns as biologically plausible strategies for promoting healthy aging through modulation of the gut microbiota; however, establishing causal relationships will require standardized microbiome methodologies, validated microbiome-derived biomarkers, integrated multi-omics approaches, and adequately powered longitudinal studies and randomized controlled trials.