High BMI good screening tool for identifying kids with elevated adiposity: Study affirms

"Among 8- to 19-year-olds, those with a high BMI were 29 times more likely to have a high FMI than those with lower BMIs," the researchers reported.

They noted that a high BMI was also predictive, though less so, of high levels of body fat percentage as well as lean mass index, for which relative risks were 12 and 15, respectively.

Although some studies have recognized the limitations of BMI, there are recent concerns that it is not a good screening tool for adiposity. Therefore, David S. Freedman, Retired from the Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues examined the cross-sectional relation of BMI to adiposity among 6923 8- to 19-year-olds in the National Health and Nutrition Survey from 2011 through 2018.

For this purpose, the participants were scanned with dual-energy x-ray absorptiometry. Adiposity was expressed as a percentage of body fat (%fat) and the fat mass index (FMI, fat mass kg ÷ m2). Lean mass was expressed as lean mass index (LMI, lean mass ÷ m2). Regression models and 2 × 2 tables assessed the relation of BMI to FMI, %fat, and LMI.

The following were the key findings of the study:

• Age and BMI accounted (R2) for 90% to 94% of the variability of FMI and LMI in each sex.
• Associations with %fat were weaker (R2s ∼0.70).
• The screening abilities of a BMI ≥ Centers for Disease Control and Prevention 95th percentile were also examined for high levels of adiposity and LMI. Cut points were chosen so that prevalences of high values of these variables would be similar to that for high BMI.
• Of participants with a high BMI, 88% had a high FMI, and 76% had a high %fat.
• Participants with a high BMI were 29 times more likely to have a high FMI than those with lower BMIs; comparable relative risks were 12 for high %fat and 14 for high LMI.

The findings showed that among 8- to 19-year-olds, BMI is strongly related to high levels of adiposity and LMI, with multiple R2s of 0.90 to 0.94 for FMI and LMI.

"Although the prediction was not perfect, a BMI ≥ CDC 95th percentile was a good indicator of a high %fat and a very good indicator of a high FMI. Participants with a high BMI were 29 times more likely to have a high FMI than those with lower BMIs," the research team wrote.

"Our findings provide further evidence of the utility of BMI in clinical care and research," they concluded.

Reference:

David S. Freedman, Babette S. Zemel, William H. Dietz, Carrie Daymont; Screening Accuracy of BMI for Adiposity Among 8- to 19-Year-Olds. Pediatrics 2024; e2024065960. 10.1542/peds.2024-065960