Does Your BMI Really Matter?

Last Friday night – just try not to get that Katy Perry song stuck in your head now – I was sitting at home all dressed up and ready for my date…who stood me up.

So, what does a single personal trainer do on a Friday night when he finds himself unexpectedly without plans? What anyone else would do, of course! I calculated my BMI! Is that strange?

Body mass index, or BMI, is used to estimate the amount of body fat a person has, based on their height and weight. Do you know what I found out? According to my BMI, I’m overweight. Friday night just got even better.

The thing is, BMI is actually not the best way to determine if someone is overweight or obese.

Since BMI only takes into account your height and weight, that means it doesn’t take into consideration the fact that someone who weighs 160 pounds may be athletic and lean with developed muscles, as opposed to 160 pounds and very sedentary with very little muscle mass.

Because muscle is more dense than fat (often it is said that, “muscle weighs more than fat,” but that’s inaccurate. Five pounds weighs the same whether it’s fat or muscle) what we really want to know is how much lean body mass we have versus fat.

I can practically hear you now saying, “But Steve, why do we even want to know how much of our actual body weight is fat? Won’t that just depress us and make us want to eat our feelings?”

Yes, it may. But the reason you should know is this: With higher percentages of body fat comes increased risks of developing diseases such as high blood pressure, heart disease, type 2 diabetes, etc.

So, if BMI is not that accurate, should we just completely disregard it altogether then? Not necessarily.

Although BMI is not a perfect measure, most people are not athletes with tons of lean muscle mass. Which means that, for most people, BMI can actually do a pretty good job of gauging how much body fat someone has. It’s still a good way to screen those who might be at a greater health risk based on their weight.

I would just say however, that if you calculated your BMI (there are several online calculators you can use, like this one at the National Heart, Lung, and Blood Institute) and it says you are overweight or obese, you might want to consider getting your body fat percentage measured with a more accurate method like bioimpedance or calipers.

BMI can be a great way to get an idea of where you are in terms of body percentage, health risks, etc. But make sure you do it with the knowledge that it’s more of a starting point for information gathering and not the final word.

I would also recommend not doing it on a Friday night after getting stood up too…but that may just be me.