The popular conception is fat = high BMI = unhealthy = chronic health conditions. Everyone basically takes this to be a true correlation. But it is NOT. So let's break it down.
What does a BMI chart measure? Oh that's right, a BMI chart is simply "a measure of body fat based on height and weight that applies to adult men and women." Otherwise stated, it's a mathematical formula that takes two numbers to create a new one. Sort of like a multiplication table! In fact look at a BMI chart without the standard "judgement" labels put on it:
Now look at a standard multiplication table:
Hmm...strikingly similar no? The BMI chart is simply a table of numbers that hold no inherent value. It is derived from taking your weight in lbs divided by you height in inches multiplied by 703. Just like a multiplication table is taking one number times another number. Simple math. If only we stopped there...but of course, we don't.
We decide to place value and judgment on those numbers so that we have a chart that looks like this:
So following our analogy we should look at our multiplication tables like this:
And even further, let's start making judgments about our multiplication table:
- 4 times 20...you really should eat a cheeseburger. You're too small. Stop being so small.
- 11 times 4...if you would just work a LITTLE bit harder you could be green ya know. Join the gym and you'll get there. You can do it.
- 8 times 23...you're kind of gross. You should be ashamed of yourself. Really, how did you let yourself get that way?
- 5 times 25...you're just flat out disgusting. You should pretty much just go away. Forever. No one should ever multiply 5 times 25. Gross.
"BUT IT'S ABOUT PEOPLE'S HEALTH! I'm just helping them live a long, healthy life! They may not know that their FAT is KILLING them!"
Complete and utter bullshit.
I've never seen a BMI chart that looks like this:
Know why? It doesn't exist! Because body fat is not a measure of health! BMI simply "measures" body fat and actually doesn't say anything about your health!You cannot use a BMI chart to predict someone's health or longevity of life. Because that's not what it measures. It measures fat. Only. Pure and simple. Furthermore, even researchers and doctors that believe in using the BMI chart for body shaming when pressed will tell you there are not CAUSAL studies that predict people's health and life longevity. There are some correlational studies, but even those are often flawed and often later retracted as BAD science. And just because something is correlated, it doesn't mean it that one causes the other. Fat does not cause poor health. Poor health habits, genetics, and other unknown factors cause poor health. Fat causes fat. We accept this in all other areas of science yet we suddenly are rendered stupid when it comes to talking about weight and health.
Are some people who are fat unhealthy? Of course. Are some "healthy weight" people also unhealthy? YES. Do all fat people have chronic diseases? No. Do some "healthy weight" people have chronic diseases? Yes. Do some fat people die young? Yes. Do "healthy weight" people also die young? Yes.
BMI charts can't predict your health or how long you are going to live.
So why do we keep using them? We'll investigate that next week