Recently, it has been hypothesized that Tri-Ponderal Mass Index (TMI) may be a valid alternative to Body Mass Index (BMI) when measuring body fat in adolescents. We aimed to verify whether TMI has better accuracy than BMI in discriminating central obesity and hypertension in adolescents with overweight.

This monocentric and retrospective cross-sectional study included 3749 pupils, 1889 males and 1860 females, aged 12–13. BMI (kg/m²) was calculated and expressed as percentiles and as z-scores. TMI (kg/m³) was calculated, and we used pre-defined cut-off previously proposed by Peterson et al.. For central obesity we adopted the Waist-to-Height Ratio (WHtR) discriminatory value of 0.5. Hypertension was defined as blood pressure ≥95th percentile of age- sex-, and height-specific references recommended by NHBPEP Working Group. The discriminant ability of TMI, BMI and BMI z-score, with respect to central obesity and hypertension, was investigated using non-parametric receiver operating characteristic analysis.

The overall misclassification rate for central obesity was 8.88% for TMI vs 14.10% for BMI percentiles and vs 14.92% for BMI z-scores (P < 0.001). The overall misclassification rate for hypertension was 7.50% for TMI vs 22.03% for BMI percentiles and vs 25.19% for BMI z-scores (P < 0.001).

TMI is a superior body fat index and it could discriminate body fat distribution more accurately than BMI. This supports the use of TMI, in association with WHtR, to characterize adolescents with overweight and high cardio-metabolic risk. Our analysis needs to be extended to other ethnic groups and replicated in a wider age range and in longitudinal studies.