Most studies investigating age-related body composition patterns focus on low-altitude populations, and whether findings from these studies apply to high-altitude populations under chronic hypoxia remains unclear. This study investigated age-related body composition patterns among native Tibetan adults from the Tibetan Plateau, exploring associations with sex and altitude.

This cross-sectional study recruited 1318 native Tibetan adults (20–85 yr) via cluster random sampling from three regions (2800, 3650, and 4500 m) in Xizang. Appendicular skeletal muscle mass index (ASMI), fat mass index (FMI), and extracellular-to-intracellular water ratio (ECW:ICW) were assessed using direct segmental multifrequency bioelectrical impedance analysis.

ASMI increased before and decreased after turning points at 43 yr (95% confidence intervals [CI], 36–50) in males and 49 yr (95% CI, 45–52) in females. FMI increased linearly in males, whereas in females, FMI increased before and decreased after a turning point at 69 yr (95% CI, 66–73). At the highest altitude, this female FMI turning point occurred earlier, at 50 yr (95% CI, 43–57). ECW:ICW increased linearly in both sexes without distinct turning points.

Among native Tibetan adults residing on the Tibetan Plateau, age-related patterns of body composition differed according to sex and altitude. Longitudinal studies are required to validate the observed trajectories and turning points before these findings can inform early monitoring of muscle loss and alterations in fat metabolism, and support the development of targeted strategies for health management in populations at high altitude.