Can waist circumference provide a new “third” dimension to BMI when predicting percentage body fat in children? Insights using allometric modelling

Introduction
Body mass index (BMI) is often criticized for not being able to distinguish between lean and fat tissue. Waist circumference (WC), adjusted for stature, is proposed as an alternative weight status index, as it is more sensitive to changes in central adiposity.
Purpose
The purpose of the study is to combine the three dimensions of height, mass, and WC to provide a simple, meaningful, and more accurate index associated with percentage body fat (BF%).
Methods
We employed a four independent sample design. Sample 1 consisted of 551 children (320 boys) (mean ± SD of age = 7.2 ± 2.0 years), recruited from London, UK. Samples 2, 3, and 4 consisted of 5387 children (2649 boys) aged 7 to 17 years recruited from schools in Portugal. Allometric modelling was used to identify the most effective anthropometric index associated with BF%. The data from samples 2, 3, and 4 were used to confirm and cross‐validate the model derived in sample 1.
Results
The allometric models from all four samples identified a positive mass exponent and a negative height exponent that was approximately twice that of the mass exponent and a waist circumference exponent that was approximately half the mass exponent. Consequently, the body shape index most strongly associated with BF% was urn:x-wiley:20476302:media:ijpo12491:ijpo12491-math-0001. The urn:x-wiley:20476302:media:ijpo12491:ijpo12491-math-0002 component of the new index can simply be interpreted as a WC “weighting” of the traditional BMI.
Conclusions
Compared with using BMI and WC in isolation, urn:x-wiley:20476302:media:ijpo12491:ijpo12491-math-0003could provide a more effective and equally noninvasive proxy for BF% in children that can be used in public and community health settings.

This is the peer reviewed version of the following article: Nevill, AM, Bryant, E, Wilkinson, K, Gomes, TN, Chaves, R, Pereira, S, Katzmarzyk, PT, Maia, J, Duncan, MJ. Can waist circumference provide a new “third” dimension to BMI when predicting percentage body fat in children? Insights using allometric modelling. Pediatric Obesity. 2019; 14:e12491, which has been published in final form at https://doi.org/10.1111/ijpo.12491. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.