Discordance Between TG/HDL Ratio and Waist-to-Height Ratio Phenotypes in Young Adults: A Cross-Sectional Study

Background: Surrogate indices proposed to reflect insulin resistance-related metabolic characteristics, together with anthropometric markers of central adiposity, have been associated with cardiometabolic characteristics, although their distributions may differ in young adults. Objective: To describe the overlap and discordance between TG/HDL ratio and waist-to-height ratio (WtHR) and examine their cross-sectional associations with selected cardiometabolic variables. Methods: A cross-sectional study included 12,874 adults aged 22–30 years. Four phenotypic groups were defined using TG/HDL > 2 and WtHR ≥ 0.5. Additional indices included TyG, METS-IR, and SPISE. Associations with fasting glucose and elevated blood pressure were examined using logistic regression adjusted for age and sex. Alternative TG/HDL thresholds were assessed descriptively. Results: The low TG/HDL/low WtHR, elevated TG/HDL/low WtHR, low TG/HDL/high WtHR, and elevated TG/HDL/high WtHR groups comprised 81.7%, 6.8%, 8.3%, and 3.2% of participants, respectively. Elevated TG/HDL without increased central adiposity was observed in 5.8% of participants with normal BMI. In the model including TG/HDL, WtHR, age, and sex, WtHR ≥ 0.5 was associated with elevated fasting glucose (aOR 2.68; 95% CI 2.14–3.34), whereas TG/HDL > 2 was not significantly associated (aOR 0.87; 95% CI 0.64–1.17; p = 0.343). Additional comparisons with fasting glucose and blood pressure showed differing patterns of association across phenotypes. Phenotype frequencies varied with the selected TG/HDL threshold. Conclusions: TG/HDL ratio and WtHR identified partially discordant cross-sectional phenotypes. These findings do not establish clinically confirmed insulin resistance, independent diagnostic validity, causal effects, or temporal relationships.