Do Gut Microbiome Aging Clocks Measure Biological Aging? A Scoping Review of Clinical Validity, Generalizability, and Translational Potential in Longevity Medicine

Gut microbiome-based aging clocks have been developed as potential biomarkers of biological aging, but it remains unknown if they reflect more than chronological aging or if they are clinically robust and widely applicable for longevity medicine. Establishing their clinical utility requires evidence beyond accurate chronological-age prediction. Two PubMed searches were performed on September 14-15, 2026, to conduct a scoping review. In total, 782 records were found, 26 reports were assessed in full text and 23 studies were included. Studies were classified into predictive aging-clock models, direct biological-aging association studies, and Mendelian randomization studies. Four studies built predictive models of gut microbiome aging, with mean absolute error around 4-9 years where reported; external validation was done only in two studies. Gut microbiome features were correlated with epigenetic ageing, frailty, physical function, immune ageing and phenotypic/metabolic ageing measures. However, taxa-level results were mixed, most studies were cross sectional, and prospective hard endpoints were uncommon. Dietary confounding further complicates the interpretation of microbiome-associated aging signals. No prospective studies showed that a gut microbiome age score predicts future clinical deterioration. Limited external validation, geographic underrepresentation, and methodological heterogeneity also created uncertainty regarding generalizability. Although gut microbiome aging clocks appear biologically relevant, existing evidence is not considered clinically validated or broadly applicable, and prospective, validated and geographically diverse studies are required.