Usefulness of the Tri-Ponderal Mass Index to Determine Body Fat Percentage in Chilean Boys and Girls Aged 9 to 14 Years

Abstract

Objective: To determine the relationship between body mass index (BMI) and tri-ponderal mass index (TMI) with body fat percentage (BFP) in children and adolescents. Methods: In this cross-sectional study, linear regression analyses were performed to assess body composition using bioelectrical impedance in 267 participants, including 149 girls (12.08 ± 1.3 years) and 118 boys (11.77 ± 1.4 years). Results: Among girls, the correlation between BMI and BFP was R² = 0.73, while the correlation between TMI and BFP was R² = 0.75. In boys, the BMI–BFP relationship yielded R² = 0.54, and the TMI–BFP relationship yielded R² = 0.66. Using BMI z-scores, 57 false positives (FP) and no false negatives (FN) were identified in girls, whereas TMI produced 12 FPs and 1 FN. In boys, BMI z-scores resulted in 47 FPs and 11 FNs, while TMI identified only 3 FPs and 1 FN. Conclusion: TMI showed a stronger association with BFP in both girls and boys. Additionally, it outperformed BMI z-scores in classifying nutritional status, presenting fewer false positives and greater applicability. The use of TMI is recommended as a complementary method to BMI z-scores for assessing nutritional status in Chilean children and adolescents.