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Longitudinal changes in BMI z-scores among 45 414 2-4-year olds with severe obesity

David S Freedman1, Nancy F Butte2, Elsie M Taveras3

  • 1a Division of Nutrition, Physical Activity and Obesity , Centers for Disease Control and Prevention , Atlanta , GA , USA.

Annals of Human Biology
|October 31, 2017
PubMed

Insights

Body Mass Index z-scores (BMIz) may inaccurately reflect changes in severely obese children. Alternative metrics like BMI as a percentage of the 95th percentile (%BMIp95) offer better insights into body size changes.

Area of Science:

  • Pediatric Endocrinology
  • Obesity Research
  • Growth Monitoring

Background:

  • Body Mass Index z-scores (BMIz) derived from CDC growth charts may not accurately represent BMI in severely obese children.
  • Age-related shifts in BMIz parameters (L and S) can complicate longitudinal and intervention studies.

Purpose of the Study:

  • To compare longitudinal changes in BMIz with BMI expressed as a percentage of the 95th percentile (%BMIp95) and a modified z-score.
  • To evaluate the utility of different metrics for assessing body size changes in severely obese children.

Main Methods:

  • Analysis of data from 45,414 children aged 2-4 years with severe obesity (%BMIp95 ≥ 120).
  • Comparison of changes in BMIz, %BMIp95, and a modified z-score (log(BMI/M)/S) over time.

Main Results:

  • Longitudinal changes in BMIz differed significantly from %BMIp95 and modified z-scores in severely obese children.
  • In severely obese 2-year-old girls, mean BMIz decreased by 0.6 SD, while %BMIp95 and modified z-scores showed minimal changes.
  • Some children exhibited BMIz decreases exceeding 1 SD despite increases in BMI, %BMIp95, and modified z-scores.

Conclusions:

  • Observed BMIz changes in severely obese children may stem from transformation methods rather than actual body size alterations.
  • Expressing BMI relative to the 95th percentile (%BMIp95) or using modified z-scores is recommended for this population.
Abstract

Keywords:
BMILMSchildrenlongitudinal

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