Q&A Wednesday: Why Does Body Mass Index (BMI) Matter?

Tricky, tricky, tricky…

Q: I keep seeing this BMI thing everywhere, and I know that my girls aren’t overweight, but their doctors tell them they are and they need to lose weight. If they don’t look overweight, why does it matter if the BMI says they are?

If the question is whether or not the body mass index (or BMI) matters… the simple answer is that in reality, it doesn’t.

No, really.

But before you go writing off your physician’s advice, let me explain it a little clearer.

The BMI is merely a calculation based on your height in correlation to your weight. It is a ratio of what one’s frame is carrying in weight, and used as an estimation of one’s health. Not necessarily their health today, but their health tomorrow.

The idea is that there is a likely height-to-weight ratio that estimates just how much weight a particular frame can manage. Anything beneath that weight can imply that your organs aren’t being supported, you might be suffering an illness or you might be malnourished. Anything above that weight can imply that you have too much fat crowding your organs, you might be suffering an illness or you are “over-nourished,” so to speak.

Look at that paragraph – see all the uncertainty? “Likely,” “can imply,” “might,” “might”… c’mon.

The BMI was invented sometime between 1830 and 1850... before slaves were freed. Think about that.

The BMI wasn’t paid much attention until approximately the 1970s (over 100 years later… think about that, too) when a guy named Ancel (An-sill) Keys created a study titled “Indices of Relative Weight and Obesity” which used the BMI, gave it its “body mass index” name and popularized the simple ratio. Calling it an adequate measure of body fat percentage in the human body, and because it was a cheaper and quicker measure than what most researchers were using at the time, the BMI spread like wildfire. Flaws and all.

I already have a problem with Ancel Keys because he’s the reason why we swear that fat is the reason we’re fat, even though we’ve now suffered through two decades of “fat free/low fat” products and are fatter than we’ve ever been. The details of his Indices study are basically that he studied approximately 7,400 men in five countries. Women? Meh, y’all and your little bodily differences weren’t needed for such a study.

In the 1980s, when the National Institute of Health began advocating the BMI for regular use in treating patients, there were differing values for men and women.. and the marking number for being “overweight” rested somewhere around 27. Once the late ’90s hit, both men and women were now to share the same standard scale, and the marker for being “overweight” was moved down to 25.

Why, you ask? If you ask this guy, he’ll tell you the NIH and the CDC were in cahoots with one another so that they could create an obesity epidemic… thus resulting in more money being given to both entities. I’m a conspiracy theorist and all, but wowzers. The change in the threshold for obesity did result in something like 30million more Americans being classified as overweight.

If there are all these problems with it, why is it still in use? Because, quite frankly, while it’s often wrong… it’s also sometimes right. Though that “overweight” label might hurt some people’s feelings (why, I don’t know), its labels like “underweight” and “obese” that signify much more than the “overweight” category. (Although, I must admit, I doubt you need a scientific calculation to identify an individual as obese. Seems like a waste of time.)

Personally, I think it’s stupid. The body responds to its environment. Some athletes are extremely active, and the body will recognize that it may need to burn calories and lose weight to help accommodate that activity. Those athletes are, by definition, underweight. Some individuals have labor intensive jobs that require lots of heavy lifting, and the body will respond by packing on the muscle. Those individuals, by definition, are overweight. My bodybuilding friends? They’re shooting the BMI the finger because they’re obese.

If the body mass index is merely meant to measure the amount of mass a body should/could carry… and we know there’s a major difference between a body carrying fat and a body carrying muscle, for our doctors to use a measurement that doesn’t quantify muscle in comparison to fat is a medical fail. Seriously. Neither Keys nor the originator of the BMI intended for it to provide such blanket assumptions in such a specific fashion. “You must be like these other people because you share the same height and weight.” That’s what the BMI says. That’s why it’s so stupid.

I, personally, find the body fat percentage to be far more valuable in gauging my physical wellness. The body fat percentage estimates what percentage of your body appears to be purely fat. The “average American female’s” body fat percentage is somewhere around 32%, while the typical athlete is around 22%.

The bf% is a much more valuable number because it acknowledges that those in the overweight category may simply be muscular, and those on the thinner side may still be hiding some fat that needs to be addressed. There is no cheating or hiding behind “unfairness” with the body fat percentage. A caliper or a hydrostatic test is usually used to measure bf% – I use an electrical machine at my gym – but there’s also this quick and dirty calculator that I use to keep track, and it only requires a tape measure. You’ll get two numbers – take an average between the two numbers, and you’ll have a better and much more valuable estimate. If body fat is the issue (not muscle), then getting numbers that address specifically that definitely helps.

Lastly, if your body mass index still has you down… head on over here and see others who, apparently, are in your “weight group” and feel a little bit better about yourself. Lots of beautiful people over there, wondering how or why this arbitrary ratio matters so much. Just like the rest of us. (This one is my personal favorite.)

PS: Show a little love by voting for me in the Black Weblog Awards for Best Health or Wellness Blog category! That’s right – BGG2WL is a finalist thanks to you! Let’s do what we can to bring it home!