Body mass index debunked

Published On: Nov 19 2012 10:08:12 AM EST   Updated On: Dec 03 2012 02:34:49 PM EST

By Tom, Pure Matters

Entering my senior year of college, I had finished all of my major and minor requirement classes and was faced with the task of filling open credits. As a college athlete and someone who had an interest in my own health, I decided to venture into a few exercise science classes. I know what you’re thinking; easy A, right? Wrong.

The cool thing about the courses I enrolled in was that the professors were passionate about their work and sincerely practiced what they preached. I’ll admit that there was a bit of head butting -- finding a balance between what my coaches said, what my professors taught, and my own experience with things like training and muscle recovery could be conflicting -- but one topic in particular had unanimous agreement: the ineffectiveness of Body Mass Index.

BMI, or Body Mass Index, is a formula used for men and women alike that takes one’s height and weight into consideration to determine their body composition. Little other information is required in assigning you a number on the BMI scale and that’s where the controversy begins.

I remember the first day of class when my professor instructed us on how to calculate our BMIs. After plugging in my numbers and checking the chart, it turned out (unbeknownst to me) that I was obese. Perplexed, I ran the numbers again to find the same result. Here I was, an early twenties student athlete who rowed 20 miles at the crack of dawn and another 20 at sunset every day and I was being pegged as obese. This couldn’t be right. My professor explained that this was a perfect example of how BMI has some major shortcomings, namely, that it tries to define individual cases by measuring on a scale of the masses.

Scientifically speaking, “because the BMI formula depends only upon weight and height, its assumptions about the distribution between lean mass and adipose tissue (Fat) are inexact.” In other words, the Body Mass Index scale tends to overestimate body fat for people with more lean muscle mass (remember, muscle weighs more than fat) and underestimate higher body fat percentages in people who may be of normal size, but don’t have much muscle.

The medical community and fitness world have gone on to recognize these shortcomings, yet still find a place for the wider scope BMI provides when considering a population as a whole. The reason is that those outliers are largely the minority when looking at most populations. Take the United States of America for example. In our country, more than 35 percent of adults are considered obese and almost 17 percent of children too. Using BMI works well here in assessing a larger sample size because it looks at averages–most people who weigh 250lbs and are are 6 feet tall will likely be on the heftier side…never mind those few exceptions popping up all over your fantasy sports league home page.

To better put the BMI’s error margin in context, here’s an example: During his 20 year career and record setting 297 consecutive NFL starts, Brett Favre, a now retired NFL quarterback, weighed in at 222lbs and stood 6’2 tall. Throw those numbers into the BMI scale and he comes out with a 28.5 BMI…that’s borderline obesity, let alone the high end of “overweight.” But if you take one look at the guy or at his Superbowl ring and record breaking statistics, I’m guessing you wouldn’t peg him as anything but muscle.

Now I’m not saying we’re all NFL players and simply misunderstood, but you should get this idea: If you are someone who is in shape and has lean muscle, there might be a good chance that your BMI score is miscalculating your body composition.

There’s no denying that Body Mass Index allows health organizations and the medical community to assess the population as a whole, but when it comes down to it, if you’re examining your own health, there are much better and more thorough ways to do it. The most simple is to start with how you feel. Walk up and down a few flights of stairs and if you’re huffing and puffing and ache all over, then you don’t need a number to tell you to consider a change in your diet, exercise, and rethinking your lifestyle. But if you’re an active person who eats healthy meals regularly and exercises, delve deeper by picking up a body fat measuring device and having your blood sugar, blood pressure, and cholesterol checked each year.

In the world of personal health, knowledge is power. Stay in tune with your body and let BMI be a tool for population analysts, not a way to diagnose your health.