BMI Affirmed as Good Screening Tool for Youth With Elevated Adiposity: Daily Dose

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Patient Care brings primary care clinicians a lot of medical news every day—it’s easy to miss an important study. The Daily Dose provides a concise summary of one of the website's leading stories you may not have seen.

Last week, we reported on findings from a study published in Pediatrics that examined the cross-sectional relation of body mass index (BMI) to adiposity among children aged between 8 and 19 years.

The study

The researchers tapped the National Health and Nutrition Survey (NHANES) for data on 8- to 19-year-olds with full-body DXA scans from 2011 to 2012 through 2017 to 2018. The primary outcome for adiposity was the fat mass index (FMI), which is often used for its independence of lean mass and the potential for a stronger relation to obesity-related diseases than %fat. They also analyzed the relation of BMI to lean BMI (LMI). Participants were scanned with dual-energy x-ray absorptiometry (DXA).

The final cohort numbered 6923, comprising 3584 boys and 3339 girls.

The findings

The investigators reported the prevalence of high BMI in girls as 19.5% and boys 20.6% (P <.05). They found much larger proportional differences in FMI and %fat. Girls had mean levels approximately 30% higher than boys. Mean LMI, however, was 10% higher for boys. Sex differences for FMI, %fat, and LMI were all statistically significant (P <.001).

Age, they found, accounted for very little (1% to 11%) of the variability seen in FMI or %fat but in boys accounted for 47% and in girls 26% of variability in LMI. Adding BMI to these models, however, “substantially increased their explained variance," with the combination accounting for 90% to 94% of variability in LMI and FMI and 68% to 71% of variability in percentage of body fat.

Authors' comment

"Although the prediction was not perfect, a BMI ≥ CDC 95th percentile was a very good indicator of a high FMI and a good indicator of high %fat. Participants with a high BMI were 29 times more likely to have a high FMI than those with lower BMIs. Our findings provide further evidence of the utility of BMI in research and clinical care."

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