Associations of body composition and visceral adiposity with BMD and trabecular bone score in young adults with obesity

Introduction The skeletal relevance of body composition in young adults with overweight or obesity remains incompletely characterized. We examined associations of body mass index (BMI), weight-normalized lean mass, weight-normalized total fat mass, and weight-normalized dual-energy X-ray absorptiometry (DXA)-estimated visceral adipose tissue mass with bone mineral density (BMD) and trabecular bone score (TBS). Methods Cross-sectional baseline data from 638 participants (aged 18–35 years, BMI ≥25 and <40 kg/m²) in the SMART 2.0 study were analyzed. DXA assessed body composition and BMD; TBS was calculated with TBS iNsight® v3. Separate age- and sex-adjusted linear models used standardized predictors and HC3-robust inference. Results BMI was positively associated with femoral neck BMD (β=0.0379; 95% CI: 0.028, 0.048), total hip BMD, and lumbar spine BMD, but inversely associated with mean TBS (β=−0.0179; 95% CI: −0.025, −0.011). Weight-normalized lean mass was positively associated with all outcomes, including TBS (β=0.0336; 95% CI: 0.024, 0.043). Weight-normalized total fat mass and weight-normalized DXA-estimated visceral adipose tissue mass were inversely associated with all outcomes; for visceral adiposity and TBS, β=−0.0321 (95% CI: −0.039, −0.025). Absolute total fat mass was positively associated with hip BMD but inversely associated with TBS. Conclusions BMI and body-composition measures showed differing associations with BMD and TBS. Given the cross-sectional design, body-size-related TBS missingness, and potential adiposity-related measurement artifacts, findings are hypothesis-generating and do not establish impaired bone microarchitecture.