The association between skeletal muscle-to-fat mass ratio and insulin resistance in obese children with low skeletal muscle mass

Obesity with low skeletal muscle mass (OLM) is increasingly recognized as a high-risk phenotype in pediatric populations. The skeletal muscle-to-fat mass ratio (MFR) reflects muscle-fat imbalance, but its association with metabolic health in children and adolescents remains incompletely understood. This study examined the associations between MFR and metabolic indicators, with a focus on insulin resistance, in children and adolescents with OLM. This cross-sectional study included 258 children and adolescents with obesity and low muscle mass. Body composition was assessed using bioelectrical impedance analysis. Skeletal muscle mass index (SMI) was calculated to define low skeletal muscle mass, and the muscle-to-fat mass ratio (MFR) was categorized into quartiles. Multivariable linear, quantile, and logistic regression models were used to examine the associations between MFR and metabolic parameters, adjusting for age and sex. Insulin resistance was assessed using the homeostasis model assessment of insulin resistance (HOMA-IR), with abnormal insulin resistance defined as HOMA-IR ≥ 3.0. After adjustment for age and sex, higher MFR was associated with lower levels of LDL cholesterol, fasting insulin, and HOMA-IR. Quantile regression analyses showed predominantly inverse associations between MFR and triglycerides, fasting glucose, and uric acid across multiple quantiles. Compared with participants in the lowest MFR quartile, the adjusted odds ratios for abnormal insulin resistance were 0.41 (95% CI, 0.18–0.92), 0.37 (95% CI, 0.15–0.89), and 0.08 (95% CI, 0.04–0.24) across increasing MFR quartiles (p for trend < 0.001). In children and adolescents with OLM, a higher MFR was associated with lower insulin resistance and more favorable levels of selected metabolic indicators. These findings suggest the potential relevance of muscle–fat imbalance in pediatric obesity and highlight the need for further research into the role of skeletal muscle mass, alongside adiposity, in metabolic risk assessment. Not applicable.