Abstract
Objectives
Despite evidence suggesting caution, employment of body mass index (BMI, kg m−2) as a proxy for percentage of body fat (PFat) in longitudinal studies of children
and adolescents remains commonplace. Our objective was to test the validity of change
in BMI as a proxy for change in PFat measured by dual-energy X-ray absorptiometry
(DXA) during adolescence.
Design
Longitudinal study.
Methods
Healthy, predominantly Australian youth of mainly Caucasian background (131 females
and 115 males) underwent repeated measures at 12.0 (SD 0.3) and 16.0 (SD 0.3) years
for height, weight and PFat (DXA).
Results
There was no significant difference in the percentage changes in BMI and PFat for
the females (β = 2.45, standard error (SE) = 1.39, 95% confidence interval (CI) = [−0.27; 5.17]) with their mean BMI increasing 15% as their mean PFat increased 18%.
However, for the males, while their mean BMI also increased 15%, their mean PFat was
reduced 25%; this change being highly significant (β = −42.25, SE = 2.23, 95% CI = [−46.22, −38.27]).
Conclusions
While change in BMI is likely to be a rough proxy for change in PFat measured by DXA
in longitudinal studies of adolescent females, this is not the case for adolescent
males, where increased BMI is likely to correspond with decreased PFat. Consequently,
inferences from longitudinal studies of adolescents which have assumed that an increase
in BMI (or BMI Z-scores or percentiles) represents an increase in adiposity require
reconsideration.
Keywords
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Article info
Publication history
Published online: August 08, 2018
Accepted:
August 1,
2018
Received in revised form:
June 30,
2018
Received:
March 2,
2018
Identification
Copyright
Crown Copyright © 2018 Published by Elsevier Ltd on behalf of Sports Medicine Australia. All rights reserved.
