After several years in development, The Centers for Disease Control and Prevention (CDC) recently released new body mass index (BMI) growth charts for children and adolescents aged 2-18 years. These charts are typically used to assess a child's growth, particularly height and weight.
Originally developed in 1977, the charts were updated in 2000 to include new BMI charts for boys and girls. Now updated again, the new charts address a major issue with the 2000 iteration, which did not have appropriate data for children and adolescents with a BMI above the 97th percentile. This issue led to inaccurate data extrapolation above the 97th percentile, primarily due to the growing prevalence of pediatric severe obesity since 2000. Therefore, the clinical and research community saw an acute need for more accurate charts. The new CDC charts address this issue with data collected between 1988 and 2016, creating real growth curves not based on extrapolation above the 97th percentile.
The new charts expand BMI plotting range up to a BMI of 60 and a BMI z-score of 5 with accuracy. Prior growth charts could not do this accurately above a z-score of around 3 nor a BMI of 37 due to the limited data points above the 97th percentile that were inaccurate at much lower levels. The growth charts also add a range of BMI percentiles from 99th to 99.9th to 99.99th. Though the statistical reasoning provided by the CDC is sound, the implementation and practicality in the real world (eg, clinical practice) will be challenging.
For example, a 16-year old girl with a BMI of 50 has severe obesity at the 99.99 percentile. She undergoes a robust treatment intervention, like bariatric surgery or the newly approved for adolescents semaglutide (Wegovy) as reported in Medscape. Over the next 9 months, she loses 20% of her BMI or moves her BMI from 50 to 40, a tremendous success.
By the new charts, the message to the patient will be vastly different. Because their BMI percentile will have only moved from 99.99 to somewhere around 99.95. Though the visual plot will show the decline in weight and the improvement, the use of BMI percentiles to relay this message doesn't reflect the improvement. This is a major flaw in disconnect with using BMI-percentile above the 99% for tracking and metric purposes for reporting outcomes. Clinicians have already identified this as problematic and will certainly work to relay this message appropriately to their patients.
This flaw in using BMI-percentiles and z-scores as well is not new to CDC growth charts. It is recommended that alternative metrics like percentage change in BMI, percentage change in percent of the 95th percentile, or percentage change in percent of the 50th percentile (median) be used for longitudinal tracking and for reporting outcomes within clinical trials.
Because the new charts have yet to be readily implemented and used within clinical trials, we will not know the true impact of them on curbing the obesity epidemic or providing more accurate data on the true scale of the problem. I believe that they will improve surveillance and tracking of obesity from an epidemiologic perspective.
Indeed, you need to be able to accurately know your targets to know the true scale of the problem you are trying to address. However, from a treatment and prevention perspective these new growth charts will probably not make much of an impact. Scientists and practitioners have known the problem's scale for years.
The clinical impact will come from using treatments that achieve significant and sustainable weight loss. Many new medications are being approved and developed for the treatment of pediatric obesity to complement lifestyle changes. In addition to the robust benefits offered by bariatric surgery, new medications have the potential to shift the landscape of a losing battle of prevention and treatment of pediatric severe obesity toward an environment showing success in reducing prevalence rates for the first time since the 1980s.
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Cite this: Can New Growth Charts Curb the Pediatric Obesity Epidemic? - Medscape - Jan 11, 2023.