Before I get into my story, let me just start by giving you the official definition of BMI. Simply said, BMI (or Body Mass Index) is a simple mathematical formula (or equation, if you will) used to calculate body fat based on height and weight. In other words, weight (in pounds), divided by height (in inches) squared, multiplied by 703 equals BMI.
Here’s a little history for you: BMI, also called the Quetelet index, was created by Adolphe Quetelet while developing what he called “social physics”, between 1830 and 1850. BMI became popular around 1972, when the Journal of Chronic Diseases published an article by Ancel Keys, which cited that BMI was an appropriate measure of body fatness for population studies. Because the formula was so simple and inexpensive, it became widely used among researchers, physicians, and dietiticians in estimating how much body fat a person has. Some people feel the need to have surgeries done to reduce body fat which you can learn more about at PeachtreeBariatrics.com. But I digress.
For children, BMI is plotted on a growth chart that uses percentile lines in order to determine whether a child is underweight, healthy, overweight, or obese. Different BMI charts are used for boys and girls under the age of 20, because body fat differs and changes as they grow and, especially, as they go through puberty. Children between the 5th and 85th percentiles are considered healthy, while children between the 85th and 95th percentile are considered overweight, above the 95th percentile are considered obese, and below the 5th percentile are considered underweight.
What you might not know is that BMI was designed to be used for population studies, in order to classify average inactive populations with average body composition. What we seem to have forgotten is that BMI was not developed to be used for individual evaluation.
I certainly understand that the cost of other forms of body measurement can be expensive, complex, and time consuming and that making parents aware of the health risks their children may endure is important; however, shouldn’t we offer a complete evaluation before telling children that they are obese? I don’t know how it is across the country, but where we live, parents receive a letter each year from the school with the first report card that gives an individual BMI assessment for each child. The school has taken their weight and height and determined whether each child is underweight, healthy, overweight, or obese. Our doctors are also required to complete this evaluation at the annual well child visit. What seems to be lacking, however, is the singular fact that this determination is based solely on a height and weight measurement of each child.
What BMI fails to recognize is (1) the fact that different body types weigh differently and (2) that muscle contributes to that weight calculation and that it weighs more than fat. BMI also does not account for varying proportions of fat, cartilage, water weight, etc.
Let’s take, for instance, my daughter. This post came about because I was told last week at my daughter’s well child visit that her BMI is off the charts and that she is considered obese (according to BMI). Let me begin by explaining to you that this girl has never been small. And when I say that, I mean that she was born at 9 lbs, 8.7 oz. That is not a small baby. But she has also never been fat.
My maternal grandmother is tall and, while healthy, has a larger frame than, say, my friend *Sarah, who is an average height but who definitely has a small frame. I have my grandma’s build. I will never be as small as Sarah no matter how hard I try, because I am not built small. And neither is my daughter.
She also is very active. This school year alone, she played soccer in the fall, basketball in the winter, and now softball in the spring. She loves to dig outside and ride her bike. I guarantee you she has more muscle mass than the inactive kids her age. Add to that the fact that I am relatively restrictive on the amount of junk food I let my kids consume. On average, she drinks less than 1 sugary drink a day, has junk food only as dessert after meals (and on special occasions), and only eats healthy snacks. This kid’s favorite snack is tomatoes. Does this sound like an obese child? Does she even remotely look like an obese child?
[singlepic id=60 w= h= float=left]Here’s another example. This is a picture of me at age 19 and at the high end of my “ideal” BMI. At 5’6″, I was 147. At my lowest weight, I was 132 at age 16. At that weight (in the middle of my “ideal” BMI), my friends began to ask if I was anorexic.
All this leads me to wonder why, if BMI continues to be the standard body fat measurement tool, we continue to tell our children they are obese when, in fact, they may not be obese at all, but healthy? If we are going to send home letters with our children telling them they are “overweight” or “obese”, shouldn’t we also investigate further to determine if this label is accurate?
There are several other tools that can be used to measure body fat, including bioelectrical impedance (a scale that measures body composition by sending a low electrical current from footpad electrodes), measuring waist circumference, underwater weighing, skinfold thickness measurement, and dual energy x-ray absorption.
Waist circumference measurements in particular, are often an indicator of risk for obesity-related diseases like type 2 diabetes, high blood pressure, and high cholesterol, according to associate professor of epidemiology and community health at the University of Minnesota, Ellen Demerath.
While it is extremely important to let parents know if their children are at risk for weight-related diseases, we also need to be certain that these diagnoses are accurate. I agree that parents need to help their children learn how to eat healthy and exercise, but there is a fine line between that and feeding our kids the lie that their body isn’t good enough no matter what size they are.
So the next time your pediatrician tells you your child is obese, you have the right to have them investigate further. Insist on further testing so you really do know whether you need to make lifestyle changes or if the label is just that–a label. And if you have a daughter, help her to understand how important it is to take care of the body God gave her but also that He loves her at any size. Here are two that we like (for girls and their moms):
“BMI for Kids: What Every Parent Should Know.” WebMD. WebMD, n.d. Web. 13 Apr. 2015.
“Body Mass Index.” http://en.wikipedia.org/. N.p., n.d. Web. 13 Apr. 2015.
CDC. “Body Mass Index: Considerations for Practitioners.” (n.d.): n. pag. CDC. CDC. Web. 13 Apr. 2015.
Gupta, Sanjay. “What’s Wrong With BMI.” EverydayHealth.com. N.p., n.d. Web. 13 Apr. 2015.
“Your Child’s Weight.” KidsHealth. Ed. Mary L. Gavin. The Nemours Foundation, 01 Feb. 2012. Web. 13 Apr. 2015.
Zelman, Kathleen M., MPH, RD, LD. “How Accurate Is Body Mass Index, or BMI?” WebMD. WebMD, n.d. Web. 13 Apr. 2015.