SUN-691 - Race-Specific BMI Z-Score Inflection Points for Insulin Resistance, Glycemia, and Dyslipidemia in U.S. Adolescents

Background: Pediatric obesity screening relies on BMI percentile thresholds that assume uniform metabolic risk across racial and ethnic groups. We aimed to define race-specific BMI z-score (BMI-z) thresholds associated with cardiometabolic risk across insulin resistance, glycemia, and dyslipidemia during adolescence.

Methods: We conducted a cross-sectional analysis of adolescents aged 12-17 years using pooled NHANES data from 5 survey cycles: 2011-2018 and 2021-2023, excluding the COVID-disrupted cycle. Outcomes included insulin resistance assessed by HOMA-IR, HbA1c, HDL cholesterol (HDL-C), LDL-C, non-HDL-C, and total cholesterol (TC). Analyses were stratified by race/ethnicity (non-Hispanic White, non-Hispanic Black, Hispanic, Asian). Survey-weighted piecewise regression models were used to identify significant BMI-z inflection points, defined as piecewise regression breakpoints, associated with changes in outcome slopes, adjusting for age, sex, and poverty-income ratio. Models estimated how metabolic outcomes changed as BMI-z increased, separately before and after each inflection point.

Results: BMI-z-metabolic relationships were nonlinear and differed by race and outcome. At lower BMI-z values, associations were relatively flat, followed by accelerated changes beyond identified inflection points. HOMA-IR demonstrated the most pronounced inflection patterns and increased steeply after inflection points across all groups (+2.5 to +5.3 per BMI-z; all p< 0.001). Interestingly, HOMA-IR inflection points occurred near the obesity threshold in White (BMI-z +1.62) but at lower BMI-z in Black (+1.17), Hispanic (+1.14), and Asian (+0.83). HDL-C declined even at normal BMI-z, with inflection points near the overweight threshold in White (BMI-z +1.00), near the population mean in Black (+0.03), and below the population mean in Hispanic (-0.26) and Asian (-0.52). HbA1c showed varied inflection points in Black (+1.65), Hispanic (+1.51), and Asian (+0.47), while White showed a linear relationship without an inflection point. Atherogenic lipid responses were heterogeneous. TC and LDL-C showed inflection points only in Asian, both at BMI-z +0.83, whereas non-HDL-C showed inflection points in White (+0.67), Hispanic (+0.04), and Asian (+0.83).

Conclusions: Cardiometabolic risk during adolescence emerges at race-specific BMI z-scores. Insulin resistance and HDL-C deterioration can occur below conventional BMI thresholds, with the lowest BMI inflection points observed among Asian adolescents. HbA1c and atherogenic lipid changes occur at higher BMI-z values and exhibit more modest or heterogeneous inflection patterns. Non–race-specific BMI-based screening may delay risk identification, suggesting benefits of consideration of race-informed metabolic assessment during adolescence.

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