Moving beyond association: the imperative for mechanistic and longitudinal research on body composition and bone...

In their cross-sectional study, Sun et al. (Aging Clin Exp Res. 2025) provide valuable evidence that the coexistence of high body fat and low muscle mass is associated with lower bone mineral density (BMD) in postmenopausal women with type 2 diabetes (T2D). While their work importantly identifies this "sarcopenic obesity" phenotype as a risk factor, our letter offers a critical appraisal to guide future research. We argue that the sole reliance on DXA-derived areal BMD is a significant limitation, as it fails to capture the deficits in bone quality (e.g., microarchitecture, material properties) that underpin the well-known paradox of increased fracture risk at normal or elevated BMD in T2D. Furthermore, the cross-sectional design and lack of biochemical data (e.g., on inflammation, adipokines, bone turnover markers) preclude any causal or mechanistic inferences about how this body composition profile affects bone.We contend that the operational definitions of sarcopenia and obesity based solely on quantity, without assessing muscle function or fat distribution, lack phenotypic precision. Moving forward, the field must adopt longitudinal designs that integrate advanced imaging (e.g., HR-pQCT) and deep metabolic phenotyping to elucidate the underlying pathways. Ultimately, this is essential for developing targeted interventions that address the intertwined pathologies of muscle, fat, and bone in this vulnerable population.