Rethinking BMI Charts for Children

Our recent blog post about the fact that BMI is an inaccurate measure of health brought up questions about BMI and children. Is BMI an accurate measure of health for children? How do the tools we use to measure growth impact our perception of children and body size?

These are big questions. But just because something has been done a certain way for a long time, does not mean we should not question it or seek to better understand its impact. And here at Eat Well Collective, we are not afraid of big questions.

Let’s dive in.

Children’s growth patterns are measured by growth charts and BMI-for-age charts. Let’s review each individually.

Growth charts:

Providers primarily use growth charts to monitor whether a child is growing appropriately. These charts indicate where your child is compared to the reference population. For example, if your child’s height is measuring at the 25^th percentile, this means that your child is taller than 25% of the reference population and shorter than 75%. There is no ideal – where a child falls on a chart is often genetic. For instance, my husband and I are shorter than average, that means our children will likely be shorter than average.

In addition, dips and jumps are normal to a certain extent. For example, at 6 months your child may be closer to the 25^th percentile and then at one year, closer to the 50^th percentile or vice versa. There may be cause for concern if your child steadily tracks close to the 50^th percentile, and then suddenly drops below the 10^th percentile. However, no single measurement should be a cause for alarm – the point is to monitor trends. These charts are primarily meant to show a pattern over time.

When looking at these charts for your child, be sure to also step back and look at your individual child and have a provider assess all factors, not just data points on the growth chart. These charts are averages and trends of how children grow and, while most children grow along these trend lines, it does not mean there will not be some variability that is normal.

One other important point of interest:

Exclusively breastfed infants grow differently than formula fed infants even after they start solid foods. WHO growth charts are more appropriate for breastfed infant growth patterns. If you baby is exclusively breastfed, be sure that your doctor is using WHO growth charts rather than CDC growth charts.

BMI charts for children:

BMI-for-age charts are used after the age of 2. According to the CDC, assessing BMI in children is important as a screening measure. These charts are essentially a comparison of where your child’s body size falls relative to other children of the same gender and age.

Current CDC growth charts do not reflect present-day population averages. These charts are not updated because, and I quote: “Because of the increase in average childhood BMI over time, updating the charts with newer data would result in a shift in the percentiles.” Aka the charts would change because average body size has changed. This means current charts are NOT an accurate reflection of today’s population.

They go on to say that: “The health implications of these higher BMI values [if we updated the BMI charts to reflect the current population] would require new research and definitions.”

Ummm…okay, yes please, let’s do that. That would be great. Without updated charts and additional research, providers are expected to operate out of the premise that larger body size in children equates higher health risks, but this may not be true. We do not know.

This is problematic because body size does NOT tell us on an individual level if someone has or is at risk of a chronic disease. This is a false assumption. BMI does not account for muscle mass, ethnicity, or the fact that BMI was not developed to tell us anything about our individual health.

The blog post I mentioned earlier includes a discussion about the origins of BMI and why we need to stop using it, so I will not repeat myself here, but suffice it to say, this applies to children as well.

BMI charts are ONLY useful for telling you what size your child is relative to other children the same gender and age. Full stop. BMI does NOT tell you how healthy your individual child is, whether they will have chronic health conditions in the future, how active they are, or how balanced their diet is. BMI can be used as a population tool, but it is entirely useless for individuals, including children.

I realize you may be pushing back on me at this point and wondering why I am not taking the research linking obesity and chronic disease seriously.

First – I always ask if a larger body size is actually a health problem or are we trained to think that because of fatphobia?

Fatphobia is cultural and rampant. We are raised to be fatphobic. It is embedded in our media, our clothing industry, and the way we think and talk. There is excellent work being done to change our fatphobic narrative, but we are still in the days of doing a lot of deep hard work both within ourselves and culturally, including in the medical field.

The medical field is a significant driver of fatphobia for all ages, including children. And I say this as someone who is part of the medical field and has a deep appreciation for medical professionals. But it remains a fact that healthcare providers often carry a deep-seated anti-fat bias, dietitians included. This fatphobia is reinforced by research that carries anti-fat bias, medical training that is entrenched in fatphobia, and tools such as BMI. Since becoming aware of my own anti-fat bias, I see how difficult it is to root out, both internally and externally.

However, despite ongoing fatphobia, there are increasing amounts of research available that makes it clear that the correlation between body size and chronic disease is not straightforward for adults. Research on adults would suggest that larger body size actually leads to living longer and does not necessarily correlate to poorer health outcomes. Might this also be true for children?

Second – let’s say that larger bodies and chronic disease are actually a problem. Most people cannot change their genetically pre-disposed body size in the long term. In addition, focusing on body size often leads to dieting which actually leads to weight gain and worse health outcomes. We would be better off ignoring body size, focusing on balanced food, improving the food system (aka providing fresh, whole foods cheaply in a communal way), and figuring out how to make movement an integral part of our lives. Our bodies may continue to be larger, but our health (for all body sizes and all ages) would improve.

To be clear, I do not want to discount the power of an in-depth conversation between a provider and a family about a child’s activity levels, food habits, social practices, screen time and so on. These things matter, particularly for our health. But the only thing that BMI charts do is shame parents into putting their child on a diet. BMI is a distraction from conversations about what really matters and setting up our children for success.

Let’s wrap up our conversation on BMI and children with a thought experiment:

Imagine if you were not worried about your child’s body size – what would you do differently? How would you handle food? How would you talk to your child about their body?

Really think about it. And then move forward as if you were not worried about your child’s body size.* This is the best thing you can do for them. When you shame a child for their eating and their weight, you teach them to be ashamed of themselves. Ellyn Satter, a dietitian and guru on teaching children to be good eaters, puts it best: “Let your child have the body that is right for [them]…if you try to make something happen, you will do damage, and it is highly likely that you will create the very growth pattern you are trying to avoid”.¹

So let’s set BMI aside and instead focus on how we can help our child have a good relationship with food and with their body. Let’s look at each child as a whole rather than focusing on body size as a sole indication of health and thriving.

If you want to dive deeper into this topic, consider reading Fat Talk by Virginia Sole-Smith.

Stay tuned next month for a longer conversation on how to raise your child to be an intuitive eater. And spoiler alert – it is more hands off than you may have imagined.