The allometric scaling of body mass and height in children and adolescents in five countries

Ponderal index classifies obesity in children and adolescents more accurately than body mass index z-scores

BACKGROUND

We aimed to compare the accuracy of the ponderal index (PI) vs. BMI-for-age z-scores transformed (BMIz) in estimating body fat levels and classifying obesity in children and adolescents from a Brazilian urban population.

METHODS

This is a cross-sectional study with 1149 participants (53.2% male), aged 6 to 18 years. Body fat percent (BFP) was obtained by multi-frequency bioelectrical impedance. Non-linear regression analysis provided the accuracy of both BMIz and PI in estimating BFP. False positive rate was obtained from the proportion of individuals placed at or above the 95^th percentile for BMIz or PI, whereas their BFP was discordantly below the 95^th percentile.

RESULTS

PI and BMIz appeared with similar stability from childhood to adolescence for both boys and girls. The portion of the variability in BFP explained by BMIz (R² = 0.74 and R² = 0.75) was close to the variability in BFP explained by PI (R² = 0.73 and R² = 0.75) for boys and girls, respectively. False positive rate was higher for BMIz compared with PI among boys (21.8% vs. 3.9%) and girls (28.5% vs. 17.5%).

CONCLUSIONS

PI is a promising index for replacing BMIz in children and adolescents due to its potential to reduce false diagnosis of obesity.