Reader Question: What’s With the New Child Growth Charts?

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I got the following question from reader Naomi

“Thanks for the information on the CDC growth charts. I wonder if you could talk about how to understand them. My pediatrician said that my child is more than 120 percent of the 95th percentile. What the h e double hockey sticks does that even mean? Help!” 

I’m happy to try to explain.

First, the information Naomi is referring to is a two-part deep dive I wrote into the creation of the CDC growth charts in 2000. You can find it here. The short story is that the intention was to take data from the National Health Examination Survey (NHES) and National Health and Nutrition Examination Survey (NHANES) data from 1963-1994 and create percentiles based on BMI (calculated from weight and height), age, and sex (male and female, with no inclusion of non-binary or transgender identities). 

The charts were not intended to be diagnostic. The original idea was that, moving forward, children would be compared to these percentiles and, understanding that there will always be kids across the spectrum including at the highest and lowest weights, healthcare providers would check on those at the high and low end of the percentiles to make sure there wasn’t something going on that should be addressed. 

It didn’t go quite as planned. First of all, kids ages 6 and up were heavier than expected in the NHANES III data (from 1988-1994). The group creating the growth charts chose to treat that as outlier data and dropped the data for ages 6 and up from their calculations, making the weight in those percentiles lower than it would have been had they included all the data they intended to. (Note, there is a lot more than this, I recommend the deep dive if you are interested in more complete information.)

Then, those with strong ties to the weight loss industry worked hard to push the medical and public health establishments to use the charts to “diagnose” children in the 85% percentile as “overw*ight” and those in the 95% percentile as “ob*se” which was, again, not the original intention of the charts. These charts stopped at 97% due to an inadequate amount of data above that percentile.

Over time, new charts and methods were created, further pathologizing youth who were larger than the data that was included in the original charts. These charts didn’t use any new data. Instead, using the conceptualization of the 95% percentile as “ob*se”, they classified kids based on the percentage over the 95% percentile of their BMI. Thus, children could be “120% of the 95th percentile.” This change was made because the original charts stopped at 97% and this “percentage over” calculation was found to be a more correct approximation than just extrapolating upward from the existing data.

At some point during all of this that I haven’t been able to precisely pinpoint someone made up the terms “very high BMI” for the 97% percentile and above (based, it seems, on the fact that it was the last included percentile) and “severe ob*sity” for kids whose BMI was 120% of the 95th percentile and above.

In 2022 new charts were created called “2022 CDC Extended BMI-for-Age Growth Charts,“ 

I checked, as I always do, and by and large the authors don’t have entanglements with the pharmaceutical industry that I could find (though the National Institute of Diabetes and Digestive and Kidney Disease, where the lead author Craig Hales, M.D, M.P.H, M.S is the Director of the Clinical Ob*sity Prevention and Treatment Program in the Division of Digestive Diseases and Nutrition is in partnership with a number of pharmaceutical companies including Novo Nordisk and Eli Lilly, makers of the new GLP-1 weight loss drugs.) That said, many of the authors are people who have pinned their careers to the paradigm of pathologizing bodies based on shared size (aka “ob*sity”)  which, while not technically considered a conflict of interest, means that it’s unlikely they are questioning anything about the current paradigm.

What this group of authors did NOT do was use contemporary data and re-norm the charts to reflect current reality. Instead, they decided that the 30-60 year old data (36-60 year old for those 6 and older) was the correct size for children to be, and then they created “extended categories” from the original chart for higher-weight youth.

They contemplated a number of methods (none of which was re-calculating percentages based on current data.) They chose the extended method. Basically, leaving the original charts, and then recalculating percentiles above that using a “nationally representative sample of children and adolescents from 1998 - 2016 who were at the 95th percentile and above (based on the 2000 growth chart data.) Using this method, they added four additional percentiles to the original charts: 98th, 99th, 99.9th, and 99.99th percentiles.

They chose this method because (info here, link includes significant weight stigma):

The extended method improves the characterization of BMI distributions at very high values using nationally representative data from more recent NHANES cycles, whereas all other BMI metrics that refer to a reference population (all alternative metrics except untransformed BMI) rely on extrapolating beyond this reference population. Second, below the 95th percentile, extended BMI z-scores and percentiles preserve CDC 2000 z-scores and percentiles that are currently in use, which allows seamless transitions from the current CDC z-scores and percentiles below the 95th percentile to extended z-scores and percentiles above the 95th percentile. 

The paper this comes from is called “Evaluation of Alternative Body Mass Index (BMI) Metrics to Monitor Weight Status in Children and Adolescents With Extremely High BMI Using CDC BMI-for-age Growth Charts”

So we’ve moved somehow from “very high” to “extremely high” Every time I read this I hear it in a professional wrestling announcer’s voice. 

Also, while the NHANES data that was used does a good job of over sampling for many minority populations, it is not fully representative as Ponce et al. explain in their 2019 report “Improving Data Capacity for American Indian/Alaska Native (AIAN) Populations in Federal Health Surveys”

The NHANES sampling methodology incorporates an oversample of Latino/a persons, nonLatino/a black persons, non-Latino/a and non-black Asian persons, low-income non-Latino/a white persons and persons of “other” race, and non-Latino/a white persons and persons of “other” race who are ages 80 and over. These categories were included as part of the weighting adjustment and stratified to match the one-year American Community Survey population totals for 2011 (NHANES 2011-12) or 2013 (NHANES 2013-14). The race/ethnicity measure that is used to stratify the weights of the NHANES data does not explicitly include an AIAN  [American Indian Alaska Native] category. AIAN HR respondents are collapsed together with nonLatino/a Native Hawaiians and Pacific Islanders, and non-Latino/a multiracial individuals, while Latino/a AIANs are contained within the Latino/a category. This means that the data do not standardize the size of the AIAN population or the distribution of different AIAN groups within this population.

Again, while I didn’t find many conflicts of interest with the authors, I do have a serious concern that the official CDC page called “Background: CDC Extended BMI-for-Age Growth Charts” cites the Ob*sity Action Coalition for respectful language. While the OAC claims to be a patient advocacy group they are almost entirely funded by, and act as a lobbying arm for, the weight loss industry - including in their claims around “respectful language.” The fact that the CDC is recommending this organization without disclosing their massive entanglements with the weight loss industry is problematic and endemic of the ways in which the weight loss industry infiltrates and manipulates healthcare.

My overarching concern is this. These growth charts have been used to pathologize and recommend “treatment” (ie: weight loss) for higher-weight children since the early 2000’s, but it doesn’t seem like kids have seen any benefit. Even using their own weight-stigma driven goal of eliminating higher-weight children, the same people who have pushed the use of these charts to pathologize and “treat” higher-weight kids are lamenting about the existence of more higher-weight kids than ever. It seems like the only people who have benefited are those who profit from selling weight loss to kids. So I have to ask, is the weight loss industry profiting while higher weight kids are being harmed? And how much better would it be for kids, mentally and physically, if the focus was on supporting the health of kids of all sizes rather than the (for-profit) focus on manipulating the weight of kids. I’d certainly like to find out.

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More research and resources:
https://haeshealthsheets.com/resources/

*Note on language: I use “fat” as a neutral descriptor as used by the fat activist community, I use “ob*se” and “overw*ight” to acknowledge that these are terms that were created to medicalize and pathologize fat bodies, with roots in racism and specifically anti-Blackness. Please read Sabrina Strings Fearing the Black Body – the Racial Origins of Fat Phobia and Da’Shaun Harrison Belly of the Beast: The Politics of Anti-Fatness as Anti-Blackness for more on this.