Aging-associated gut dysbiosis — marked by depletion of short-chain fatty acid (SCFA)-producing bacteria, accumulation of lipopolysaccharide (LPS) and trimethylamine N-oxide (TMAO), and disrupted bile acid metabolism — systematically tilts the osteoblast-osteoclast axis toward bone resorption via NF-κB-mediated chronic inflammation and impaired intestinal barrier integrity. Exercise and dietary fiber partially reverse these shifts by elevating SCFAs, though this 56-article narrative review acknowledges substantial translational gaps and inter-individual variability.
This review arrives at a genuinely useful intersection: the well-documented gut-bone axis is increasingly credible, with SCFAs like butyrate known to inhibit osteoclastogenesis and support regulatory T-cell populations that protect bone density. What's compelling here is the proposed stratification framework — classifying patients as microbiome "sensitive" or "resistant" and tailoring rehabilitation accordingly, using fecal SCFA-to-calprotectin ratios as candidate biomarkers. That's a clinically actionable concept, though it remains entirely hypothetical without prospective cohort data.
The limitations are significant: this is a narrative review, not a meta-analysis, and the included evidence spans heterogeneous animal models and elderly populations aged ≥60. Polypharmacy confounding in older adults — antibiotics, PPIs, metformin — can independently reshape the microbiome, complicating attribution. Overall, this is confirmatory rather than paradigm-shifting, synthesizing existing mechanisms into a precision-rehabilitation hypothesis that deserves rigorous prospective testing before clinical adoption.
