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Study supports BMI as an accurate screening tool for body fat in children, teens

June 3, 2024

Children and teens with a high body mass index (BMI) were significantly more likely have high levels of body fat, supporting BMI as a useful screening tool, according to a new study.

“Despite its limitations, a high BMI is a very good screening tool for identifying children and adolescents with elevated adiposity,” authors wrote in “Screening Accuracy of BMI for Adiposity among 8- to 19-year-olds” (Freedman DS, et al. Pediatrics. June 3, 2024).

BMI is a commonly used screening tool and is recommended in the AAP’s 2023 Clinical Practice Guideline for the Evaluation and Treatment of Children and Adolescents With Obesity. For youths, the BMI calculation of weight divided by the square of height is interpreted through age- and sex-specific growth charts. However, the AAP and others have acknowledged criticisms that BMI cannot distinguish between fat and lean mass, nor characterize the distribution of body fat.

Researchers set out to determine the validity of BMI using nationally representative data on nearly 7,000 children ages 8-19 years. Their fat mass and lean mass were measured using dual-energy X-ray absorptiometry, the gold standard in body composition measurement.

Authors found most of the variability of fat mass index and lean mass index in each sex could be attributed to age and BMI.

About 88% of children with a high BMI (at or above the 95th percentile) had a high fat mass index. In addition, those with a high BMI were 29 times more likely to have a high fat mass index than those with a lower BMI, nearly double the relative risk of having a high lean mass index.

“Our findings provide further evidence of the utility of BMI in research and clinical care,” authors wrote.

Experts who wrote a related commentary said while more tools are needed to assess fat distribution and risk of obesity-related disease, pediatricians can feel confident in using BMI as a screening tool for high body fat. They said BMI should be “1 piece of a more holistic approach,” echoing the AAP’s guideline.

“Additional risk stratification for how a specific BMI affects an individual’s health should be person-centered and include additional data from the history and diagnostic testing,” commentary authors wrote. “Further, treatment goals should be focused on health and quality-of-life outcomes, as opposed to a number or percentile on a growth chart.”



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