Across two large population-based cohorts — CHARLS (n=15,701 Chinese adults) and NHANES (n=10,730 Americans) — higher adiposity was inversely associated with sarcopenia risk, but this apparent protection was almost entirely concentrated in individuals with high relative grip strength (RGS, defined as grip strength divided by body weight). For BMI, the inverse association was roughly 10-fold stronger in high-RGS individuals (OR 0.64) versus low-RGS individuals (OR 0.97), with a waist-circumference interaction reaching p=6.19×10⁻²⁴. Among participants with already-impaired grip strength, the association vanished entirely. Triglycerides mediated approximately 10.5% of the total effect, suggesting mostly direct biological pathways remain uncharacterized.
This preprint — not yet peer-reviewed — offers a compelling mechanistic resolution to the long-debated obesity paradox in sarcopenia research. The field has struggled for years to reconcile epidemiological studies showing both protective and harmful adiposity effects on muscle health; stratification by functional capacity rather than mass alone may be the key missing variable. Practically, these findings suggest that adiposity readings carry little diagnostic meaning for muscle health without concurrent functional assessment. Clinically, body weight alone is an insufficient screen — grip strength testing becomes essential context. Important caveats apply: this is cross-sectional data, precluding causal inference, and the diagnostic circularity concern (grip strength appearing in both modifier and outcome) was addressed but deserves further scrutiny in longitudinal designs. The dual-cohort replication across culturally distinct populations strengthens confidence considerably, making this a potentially paradigm-shifting contribution pending formal peer review.
