Year: 2024
Type: editorial
Abstract: BMI is widely used clinically and its application was recently reinforced by the first clinical practice guideline for childhood obesity from the American Academy of Pediatrics. 1 The first key action statement in this guideline is for pediatric providers to assess age-and sex-specific BMI percentiles at least annually for youth 2 to 18 years old (Grade B).The relationship of weight (in kg) divided by height (in meters) squared was originally derived by Belgian mathematician Adolphe Quetelet in 1832 (originally termed the Quetelet Index) as a way to describe vertical and transverse human growth, particularly outside of infancy and puberty. 2 In 1972, physiologist Ancel Keys proposed this same equation, renamed the "body mass index," as a preferred way to describe relative weight as it pertains to "body fatness" on the basis of validation data from a multinational sample of men. 3 Showing foresight in this seminal article, Keys cautions against attaching value judgments about human behavior to changes in body metrics.Over the last 50 years, including recently, BMI has been criticized as a rudimentary, antiquated metric with a major flaw being its detachment from a direct measure of adiposity.4,5 Compared with absolute BMI cutoffs used for adults, pediatrics leverages age-and sex-specific growth charts from the Centers for Disease Control and Prevention to define underweight, average, overweight, obesity, and severe obesity.6,7 Newer approaches to body composition analysis, including digital anthropometry and associated machine learning (ie, generating a three-dimensional model of the body using a digital scanner and pairing with a database that matches the body shape/measurements to body composition), aim to be fast, accessible, cost-effective, and personalized.8 But to date, none have proven better than BMI in the clinical setting.In this issue of Pediatrics, Freedman et al evaluate the relationship between BMI and adiposity within a contemporary cohort of 6928 8-to 19-year-olds in the United States using National Health and Nutrition Examination Survey data.9 A key finding is that the combination of age and BMI predicts the vast majority (90%-94%) of the variability in dual-energy x-ray absorptiometry-measured fat mass and lean mass indexed to height within each sex.And, although BMI $95th percentile is associated with both increased adiposity and increased lean mass, the likelihood of increased adiposity was about twice as high as the likelihood of increased lean mass (relative risk 29 vs 15).Notably, the association between elevated BMI and increased adiposity is very strong for youth with BMI $95th percentile, but is not for youth with lower BMIs, including in the overweight range (BMI 90th percentile).Stark sex differences in the pattern of lean versus adipose tissue accretion over puberty are also redemonstrated in their analysis, where a steady increase in the fat mass index is seen only in girls across the entire age range studied, whereas a near-linear increase in lean mass index over this age range is seen only in boys.This study by Freedman et al serves to reinforce the clinical utility of BMI, particularly in identifying increased adiposity in the obesity range.Strengths of this study include the use of a gold standard for body composition (dual-energy x-ray absorptiometry), evaluation across the full BMI/adiposity spectrum, and inclusion of practical screening characteristics (eg, positive predictive value) to describe associations between BMI $95th percentile and body composition.
Source: PEDIATRICS
Authors: Jaime M. Moore, Stephen R. Daniels
Institutions: Children's Hospital Colorado, University of Colorado Anschutz
Language: English
Subfield: Physiology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W4399298652