The Role of Gender in the Relationship Between Waist-to-Hip Ratio, Triglyceride–Glucose Index, and Insulin Resistance in Korean Children

Background/Objectives: Little is known about the relationship between obesity, the triglyceride–glucose (TyG) index, and insulin resistance (IR). This cross-sectional study of Korean children investigated whether the TyG index mediates the relationship between the waist-to-hip ratio (WHtR) and homeostatic model assessment for IR (HOMA-IR). Methods: Six-hundred-and-thirteen Korean children (320 boys and 293 girls) aged 9–12 years old participated in this study. The participants were classified as insulin-sensitive or insulin-resistant based on gender-specific cut-off values of HOMA-IR. The TyG index was calculated as follows: ln [fasting triglycerides (mg/dL) × fasting blood glucose (mg/dL)/2]. Results: Children with IR were older, more likely to be girls, and had fewer favorable metabolic risk factors than children without IR. A mediation analysis revealed that while WHtR has a direct effect on HOMA-IR, it also has an indirect effect on HOMA-IR through the TyG index. The bootstrapped 95% confidence interval (CI) confirmed that the TyG index had an indirect effect on the relationship between the WHtR and HOMA-IR (effect = 0.349, SE = 0.075, 95% CI [0.210, 0.504]). The interaction effect between the WHtR and sex for the TyG index was statistically significant (β = −1.369, SE = 0.631, 95% CI [−2.608, −0.129]), but it was no longer significant when vigorous physical activity was considered as a covariate. Conclusions: Our findings suggest that girls are more vulnerable than boys to an increase in the TyG index caused by an increase in WHtR. This gender disparity observed in the study needs to be investigated causally.