Why BMI is Bullshit

Oh, the magic “BMI 19.”

“Get to a BMI 19 and you’ll be healthy,” they tell us.

Bullshit. Utter crap. Hear me out…

Body Mass Index (BMI) is a very basic, and arguably erroneous, way to estimate the amount of fat that a person has on their body based on their height and weight.

Even the bloke who invented BMI (Adolphe Quetelet who published his “Quetelet Index” in 1832) said that it should not be used as a measure of fat on a person’s body. It is nonsensical in a scientific sense, as it makes no allowance for the relative proportions of a person’s muscle, bone, and fat. And guess who is responsible for turning the Quetelet Index into “Body Mass Index?” None other than our old pal Ancel Keys, whom I have a love-hate relationship with, as although Keys is responsible for the misguided war on fat (for which I will always be cross with him), he also did the Minnesota Starvation Study.

Okay, back to the present. Ironically, although the CDC uses BMI as a measure of health, the CDC’s own data show that BMI measures are inaccurate at determining … well, just about anything really. You can be the exact same height and BMI as someone else and have very different bodies. Oh, and not to mention that very same data shows that nearly half of the people classified as “obese” by the BMI standard were perfectly metabolically healthy, actually. That’s because the human body is an organism not a fucking math equation.

It’s all rather embarrassing now really. Most medical practitioners seem to know deep down that BMI isn’t really a reliable indication of health, yet they still pull out that dumb chart and trace lines along it. It’s like a fly that won’t go away no matter how many times you bang your head against the wall.

The reason I get riled up about this is because something that absolutely should not be used as a measure of health is the most commonly bloody used measure of health for people in recovery from life-threatening restrictive eating disorders. Again and again and again. It’s like using leeches to treat a fever — might have seemed like a good idea before we knew better, but now we know better. I imagine that if your doctor started trying to put leeches on you every time you got a fever you’d run a mile. (I actually don’t know very much at all about leech therapy, so I shouldn’t judge. Apologies to any leeches who are actually wonderful healers.)

It’s hard enough to convince people with eating disorders that they are in a state of malnutrition as it is. The last thing you need is a stupid chart on the doctors office wall telling you that you are healthy when your mental state is a shit show because your body is in malnutrition and one part of your brain is desperately telling you to eat and the other part is screaming at you not to. Oh, how wonderful that a little chart on the wall that was thought up by someone a couple centuries ago on a whim knows more about your body than your actual body does. Never mind that your hair is falling out. Never mind that you think about food the whole time. Never mind that you are in a constant state of anxiety. Never mind that your heart rate is still dangerously slow. No, the chart says you are okay, so you must be okay.

Bollocks. Utter bollocks.

In the video below I explain why a BMI of 19 does not equal nutritional rehabilitation for every person who has a restrictive eating disorder. I don’t even yell. But I feel like yelling about this all the time because it is so ludicrously stupid that anyone would ever have thought that was the case. Let alone that many people still do think that it is the case — people with degrees at that! I mean, I didn’t even go to around 80 percent of my lectures at university, yet even I can look at a standard distribution graph and see the problem with recommending that everyone should be at a weight that is below that of the general population.

It’s like treating anorexia with anorexia. Here, put on some weight, but let’s try and control how much weight you put on and when, because wouldn’t it be the end of the world if you actually put on enough weight to be anything other than underweight … 

So for those of you who don’t like to watch videos, here is my explanation:

BMI ranges (underweight, healthy, overweight etc) are based on a bell curve of the population. So, even if we were to use BMI as a indicator of nutritional rehabilitation (which we should not) why the heck are we being told that everyone is “healthy” at a BMI of 19, when a BMI of 19 is below the average for the human population? BMI 19 has just got its foot in the door of the “healthy” range. It hasn’t even taken its coat off yet. It could visit the loo and come out underweight.

When we assume that BMI 19 is “recovered,” we are assuming that every person in recovery would be a person with a naturally low bodyweight once recovered. There’s a nice chuck of misinformation that doesn’t recognize that eating disorders affect people in all sizes of body.

As I explained in last weeks post, if your natural, unsuppressed bodyweight is a BMI of 26, and you are only nutritionally rehabilitated to a BMI of 23, then you are suppressing your bodyweight and you are underweight. If you stopped at a BMI of 19, then you are very underweight!

Mental state is what indicates your nutritional rehabilitation status. Not your weight. And not some BMI pie in the sky.

Do you know what makes me really proud of people through? The emails I get from people in recovery telling me that although their doctor has told them that they are recovered, they know that they are not, and that they are going to push on challenging restriction and allow that higher, unsuppressed bodyweight and see what happens. Because they know that they know better. They know that they are not “okay” and they know that they can’t settle for a half life. And that is amazing, because everyone deserves full recovery.

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