Association of Body Compositions and Bone Mineral Density in Chinese Children and Adolescents: Compositional Data Analysis

The purpose of this study was to investigate the relationship between body compositions and bone mineral density (BMD) and the effect of composition substitution among Chinese children and adolescents without the influence of multicollinearity. A dual-energy X-ray absorptiometry scan was used to determine the amount of truncal fat (TF), nontruncal fat (NTF), fat-free mass (FFM), and BMD. The compositional data analysis and the compositional proportional substitution analysis were conducted to determine the effect of each part of body compositions on BMD and its substitution effects. Four hundred sixty-six (466) (boys: 51.9%) participants completed this cross-sectional study. For girls, in the overweight group, the relationship between TF and the BMD was positive (β = 2.943e − 01, p = 0.006) while the NTF showed the opposite trend (β = −2.358e − 01, p = 0.009). When 4% NTF or FFM was substituted by TF, the BMD increased by about 0.1 and 0.05 units (p < 0.05), respectively. For boys, the association between FFM and BMD was statistically positive (β = 4.091e − 02, p = 0.0001). There was a positive correlation between TF and BMD (β = 7.963e − 02, p = 0.036). But with the increase of BMI, this correlation shifted in the opposite direction. In conclusion, compared to TF and NTF, FFM had a better protective effect on BMD, especially for boys. The risk of NTF accumulation on BMD was greater than that of TF accumulation. Compared with girls, boys were more sensitive to the amount of TF.