High BMI with Adequate Lean Mass Is Not Associated with Cardiometabolic Risk Factors in Children and Adolescents

Background: Despite an increasing number of studies investigating the links between increased BMI and a better prognosis of cardiovascular disease, which has been termed the "obesity paradox," few of them take the lean mass into consideration. Objectives: This study aimed to explore the associations of body composition compartments, especially the leanmass, with cardiometabolic abnormalities in children and adolescents. Methods: In a nationwide cross-sectional study of 6- to 18-y-old children (n = 8967, 50.1% boys), we measured body composition using DXA scan, and calculated BMI, fat mass index (FMI), and lean mass index (LMI). The exploratory outcomes were cardiometabolic abnormalities, including hypertension, dyslipidemia, hyperglycemia, and insulin resistance. Adjusted linear regression coefficients and ORs were calculated to assess the associations between body composition indicators and cardiometabolic abnormalities. Results: Unlike BMI and FMI, LMI was inversely associated with homeostasis model assessment of insulin resistance (beta: -0.06; 95% CI: - 0.09, -0.03; P < 0.001), fasting plasma glucose (beta: -0.08; 95% CI: -0.11, -0.05; P < 0.001), non-HDL cholesterol (beta: -0.10; 95% CI: -0.13, -0.08; P < 0.001), LDL cholesterol (beta: -0.12; 95% CI: -0.14, -0.09; P < 0.001), and total cholesterol (TC) (beta: -0.16; 95% CI: -0.19, -0.14; P < 0.001). After multivariable adjustment, all the odds of cardiometabolic abnormalities were increased from the lowest quartile to the highest quartile of BMI and FMI (P-trend < 0.05); however, the odds of high TC, high LDL cholesterol, hyperglycemia, and insulin resistance were decreased with LMI (P-trend < 0.05). Obese children with high LMI did not have significantly increased odds of high TC, high LDL cholesterol, and high non-HDL cholesterol compared with normal-weight children without high LMI. Conclusions: Greater lean mass may have a protective impact on high TC, high LDL cholesterol, hyperglycemia, and insulin resistance in children and adolescents. This finding suggests that the "obesity paradox" may be partly explained by high lean mass.