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Aspire Fitness

Is the BMI table’s 15 minutes of fame over?

Our Take
Pushups to Pinups

I was recently asked my opinion on an article published by The Daily Mail regarding the validity of the old BMI chart that can be seen plastered on the walls of so many doctor’s offices. This is something I have spoken about before, and all though I don’t feel it’s the best tool for body composition, it does have its purpose.

Just because it has a purpose doesn’t mean it’s helpful. The BMI chart is a measure of body density. It is easy to find your BMI if you take your weight (in kilograms) and divide it by your height (in meters) twice. The resulting number will be your BMI. According to this calculation if it fits within a range you’re deemed to be healthy. There are a lot of problems with this, the most obvious is that it isn’t actually measuring your body composition. All the formula does is show how much one square meter of your body weighs. Different tissues have different masses. What we should be more concerned about is the composition of our bodies.

We’re made up of many different things: skin, bones, muscles, fat, blood, and organs just to name a few. Each have their own unique densities. Therefore, we really do need to find a better option than the BMI chart. The post suggests using a waist-to-hip ratio, something we’ve used for years with our Push-Ups to Pinups and now Grit to Glory. It is a simple measurement, though it takes longer to determine than BMI, where we simply look to ensure that the circumference of your hips is greater than your waist. Professor Janet Tomiyama maintains that this is a better health indicator than the now archaic BMI. The major concern is that the BMI chart has been used to determine insurance premiums and has been falsely identifying people as healthy and some as unhealthy.

The insurance industry has used many different tests to determine a customer’s health risk. In 1959 MetLife Insurance used a table that would use your gender, height, weight and body frame size. The problem was that there was no test for body frame size it was simply “eyeballed”. In the 80s MetLife added elbow breadth (width from side to side) to determine body frame size. Due to the nature of the insurance industry, a quick test to determine risk is needed. The compromise with quickness is that you lose some validity.

It is important to understand that these tests in the scope of your health need to be taken with a grain of salt. Regardless if you’re using the BMI table, MetLife’s table, waist-hip circumference or any of the other quick tests out there, they are designed to generate false positives. The idea is then to be referred to another professional who can properly test body composition. That’s where people like us come in. When we do any sort of body composition testing we choose a range of tests. When testing composition there are always assumptions made, even the gold standard under-water test (hydrostatic weighing) assumes that everyone has the same residual volume of air in their lungs, as well as any other parts of your body that hold air, think intestines. We choose three different tests, we use a Bio-electrical impedance analysis (a fancy array of words that simply mean we put you on a scale and it does some fancy math). On top of the BIA scale, we will do skinfolds and circumferences (including waist-hip circumference). We choose such a large array of testing to account for the unique error present in each test. Then we use our knowledge and experience to determine a healthy range.

What is a healthy body fat percentage? It’s not a question that can be answered simply. We use a chart to determine a healthy range, the chart takes into account your age. As you get older the healthy range increases. So it is possible that you’re too young for your body fat.

What’s the take home point of this whole post? Be a critical thinker. We’ve had people come into Aspire and tell us that according to the BMI table they are 10lbs over weight. Upon closer inspection we determine that they are in fact a healthy range. Or on the other end of the spectrum, people come in here say they are a healthy body weight (according to the BMI table) but after we do some testing we may determine they are outside a healthy range. It’s important to know that I’m not knocking any doctors or other health care professionals who use something like a BMI table, it was designed to be quick and for that reason it has been very useful. However it’s 15 minutes of fame may be over. Time to move over for another test, the waist-hip ratio. Regardless of what is hanging up in the doctor’s office it is important to seek a second opinion that may have more resources to test more thoroughly.

With regards to body composition testing something my Exercise Physiology prof Dr. Liz Ready at the University of Manitoba said has always stuck with me, “The only accurate way to measure body fat is dissection”. This method unfortunately doesn’t allow follow up tests, so it’s something we typically avoid. 😉