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BM(Freaking)I – How accurate is the Body Mass Index?

UntitledThe Body Mass Index (BMI) chart is used to gauge a healthy weight for people and used by a lot of doctor’s offices, personal trainers, dieticians, and other health professionals, but is the BMI flawed? How accurate is the BMI chart, and should you use it to determine your level of health?


What is BMI?


BMI is a calculation to determine one’s healthy weight by taking into account height vs. weight. The calculation is then compared on a chart to determine if you are underweight, normal, overweight, or obese.


Here is how you can calculate BMI:


English BMI Formula

BMI = ( Weight in Pounds / ( Height in inches x Height in inches ) ) x 703

Metric BMI Formula

BMI = ( Weight in Kilograms / ( Height in Meters x Height in Meters ) )




Confused? Click here for a calculator to find your BMI.


I’ll use myself as an example:

Height: 68”

Weight: 160 (give or take)


(160 / (68 X 68)) X 703 or (160 / 4624) X 703 or 0.03460207612457 X 703 = 24.33


My BMI = 24.33


Now I compare that number to a chart:


Below 18.5 – Underweight

18.5 – 24.9 – Normal

25.0 – 29.9 – Overweight

>30.0 – Obese


So currently I fit into the “normal” range. If I were to gain 5 pounds of muscle, I would be “overweight” according to the BMI chart.


So how accurate is the BMI Chart and calculations?


Well, nobody has ever said that BMI is the “be all, end all” measurement of health. Even the CDC website states that the calculation is “fairly reliable” noting that it may be inaccurate for highly trained athletes and other individuals with variables relating to race, sex, and age.


So certain types of athletes defy the BMI chart.


Let’s take an example of two NFL stars:


Adrian Peterson, considered one of the league’s top running backs has the following stats:


Height: 6’1”

Weight: 217

BMI: 28.63 (Overweight)


Maurice Jones-Drew, another leading running back:

Height: 5’7”

Weight: 210

BMI: 32.89 (Obese)


Obviously neither of these men is overweight or obese, and both are in fact among the elite of the world when it comes to physical shape.


What about those that are not NFL stars? Here is another example of how the chart can be flawed – and I’m just going to be blunt about it.


Jenny is 5’2 and weighs 125 pounds, which puts her in the “normal” range. Her friend Michelle has wears the same size jeans as Jenny and is the same height, only Michelle has a slightly bigger butt and wears a D cup bra compared to Jenny’s B. Plus Michelle works out a little more and has some more muscle on her legs. So Michelle weighs in at 136 – overweight. Michelle gets penalized on the BMI chart for having curves.


And of course, there are women athletes that can throw off BMI scales and even men that are just naturally bigger than most other guys.


Is measuring BMI accurate for you?


BMI is pretty accurate for a lot of people, but not everyone. Yes, muscle weighs more than fat, but truth be told, muscle does not just pile on your body overnight. If you do train a lot and have a lot of muscle; if you look in the mirror and see a linebacker or Olympic weightlifter; if your jeans are getting looser on the waist and tighter on the thighs – then the BMI chart might not be the best measure of body composition.


On the other hand, if you are going to a fitness class a few times a week, doing a round of P90X, or doing any other sort of recreational fitness with a good nutrition plan, then the BMI will most likely be a pretty good measurement. As shown with my own example, I am pretty close to being “overweight.” It would take quite a bit more muscle to put me into the “obese” category making the chart completely flawed. But at my current weight and body composition it is fairly accurate. And furthermore, if I were to put on another 5 pounds of muscle I would probably shed a pound or two of fat in the process for a net gain of just a couple of pounds. Remember muscle weighs more than fat, but it also burns fat!


So be honest with yourself. BMI may show individuals are overweight when they are actually fit and muscular, but rarely does a BMI reading of obese show there is no excess body fat. Maurice Jones-Drew and those with a pro athlete-like physique similar to his are the exception to the rule. If you look like him, then you are probably unconcerned with this article. If your BMI is telling you that you are overweight or obese, take a look in the mirror. See how those jeans are fitting. Pull out the tape measure and even invest $5 in a body fat caliper. If you are fitting into a waist size you wore in high school and you are finding yourself with not a lot to grab with a fat caliper, then you are good to go!


BMI  (Body Mass Index) might not be the perfect measure of success with body improvement, but it is good place to start for most people. I don’t think it should ever be the only thing you use, and if you are a linebacker of bodybuilder you can probably throw it out completely. But for the rest of us, the BMI measurement has its place among bathroom scales, tape measures, body fat calipers, and jeans sizes – not the perfect measurement, but fairly reliable.

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