Yes Virginia, BMI is BS

BMI or body mass index is a number that is generated by dividing someone’s weight in pounds by their height squared and multiplying the result by 703.  This simple ratio of weight and height is now used as a measure of health.  And that’s a problem.

Belgian polymath Adolphe Quetelet devised the BMI equation in 1832.  He created the formula to be used as a statistical tool across large populations, he never intended for the number to be used as a measure of individual health.  When people say that BMI is a poor measure of health, that’s not accurate.  The truth is that BMI is not a measure of health at all.

The idea that there is an “ideal bmi” is called into question by the fact that in 1998 the “ideal/healthy BMI” was changed.   Three members of the committee responsible for making the recommendation had direct ties to pharmaceuticals that manufactured diet pills for profit.  A fourth member was the lead scientist for the program advisory committee of Weight Watchers International.  This committee advocated dieting for everyone who had a BMI more than 24.  They shaved 15-20 lbs off the definition of “ideal/healthy weight” which made about 29 million Americans “overweight, ” and thus “unhealthy,” overnight.  It also gave those making the recommendations 29 million new potential clients.  Now there is talk of lowering the BMI again. So it’s difficult to defend the idea that, even if there was an “ideal height/weight ratio”, we have any idea what it is.

Beyond that, the research linking a higher BMI with diseases is correlational, meaning that they happen at the same time.  That doesn’t mean that you can assume that BMI causes the diseases or that you can assume that decreasing BMI will cure or prevent those diseases.  Often in August the most ice cream is eaten and the most murders take place, but we can’t assume that taking ice cream off the shelves will decrease the murder rate.  Correlation never implies causation because it’s possible that the two things are unrelated or that a third thing causes both issues (in this case maybe heat increases the propensity for murder and the chances that people eat ice cream?)

People often ask me how I can “ignore” all of the correlational evidence that having a high BMI is unhealthy.  I’m not ignoring it, I’m simply putting it to the scientific rigor that it deserves.  It turns out that the same diseases that are correlated with high BMI are also correlated with being under a high degree of stress over a long period of time.  Like, perhaps, the stress of living in a society where the government wages war on you for the way you look?  Either way, this issue is absolutely not as cut and dried as we are lead to believe.

The use of BMI is cheap, lazy, bad medicine.  We don’t need BMI to be a middleman between us and our health, because we can measure metabolic health, we can measure strength, stamina, and flexibility and we can work on those things if we want to without trying to change our body size or shape.

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13 thoughts on “Yes Virginia, BMI is BS

    So much yes!
    What boggles the mind is that, despite this ever growing “obesity epidemic” they keep banging on about, not one study, not one person or organisation, has yet to establish how all us fatties are supposed to lower our fat-assed BMIs to something more socially acceptable. And now they want to lower the threshold again? Give me a freakin’ break. I’d like to think that this extra push will be just what the populace of the western world needs to realise this BMI stuff is all a bunch of hokum.

  2. According to the current BMI standards, Johnny Depp is overweight. Having seen pictures of him where he’s shirtless and his pants are worn a tad low, I know that his hipbones are clearly visible to the naked eye.

    Somehow I have had great difficulty reconciling those two facts… oh, until I realized that BMI is as misused as IQ.

    Yeah, that one was never meant to be a measure of intelligence. Its original purpose was to identify children with borderline learning disabilities so they could get the help they needed in schools. Intelligence and learning disabilities are two different things that may or may not occur together… sort of like a large waistline and disease.

  3. It’s important to remember that Quetelet was trying to associate body size with criminal behavior. From the very beginning, bmi was about scapegoats and blame.

  4. I think it’s also telling that, societally, we:

    1) Place so much less emphasis on conditions and diseases that are correlated with low BMIs (whether as a potential risk factor or as a potential side effect).

    2) In the case of conditions associated with low BMI — virtually never suggest that raising BMI in and of itself will mitigate the condition or disease.

    If society really accepted that changing BMIs was the appropriate solution to health issues correlated to particular types of BMIs, shouldn’t it go both ways? (I mean, I still think it would be misguided, but at least it would be consistently misguided.) That the predominant societal message is about lowering BMIs to avoid/mitigate/magically cure disease is yet more evidence that this is about fat prejudice rather than anyone’s health.

  5. Hold on. They’re thinking about changing the BMI ranges again?! Where did you read that? (I’m not doubting you, I just had not read about that and find it, obviously, distressing.)

  6. I remember when the transition from height-weight charts to BMI started, and Prevention magazine had a whole article about what was wrong with BMI for measuring health (like how it doesn’t take into account gender, bone density, OR muscle mass, and therefore inevitably goes sideways in dealing with physically active women in particular).

    Within a year, without any of those valid issues having been addressed, Prevention changed its tune so it could get in on selling diets. (Better ones! Ones THEIR publishing house were putting out!) Within a year after that, I canceled my subscription.

  7. I posted what BMI is actually an acronym for in the latest Shakesville Fatsronauts series…. Bullshit Medical Inference.

  8. Oh dear God…this is why I ‘gained’ an eating disorder? I suspected something when the doctors measured my BMI and called me ‘obese’ at 14. It makes me so so so angry. I wish I knew better, actually I wish they knew better. Maybe this is a psychological reaction but I feel that when anyone brings up BMI it feels like such a huge scientifical fact and you’re totally screwed and unhealthy. Almost nobody can dismiss it as a big steaming pile of crap that it is.

    This works both ways, a naturally skinny person could be called malnourished and starving just based on that damned number.


  9. The thing is when I was obese, everyone told me fat-shaming is a myth. How thin privilage does not exist. I am no longer obese. In fact, I am considered tiny, and let me tell you how much nicer everyone is to me. I always was sexually harassed, even when obese, so that hasn’t changed. But normal interactions have. Interactions with my doctors have. With teachers and counselors and everything.

    My friends have always treated me the same, so I’m grateful for that, but how my heart breaks for one of my best friends. The way people treat her makes me want to scream at them.

    When I know someone who is obese, I listen. I know their struggles! I wish I had known this blog when I was obese. I wish there had been something like this. You’re doing a really great thing here, and I hope you can inspire more people.

  10. Another problem with BMI, for women especially, is the taller you are, the more screwed up BMI is. I am six feet tall, and have suffered from an eating disorder since I was ten years old. At my unhealthiest, skinniest and sickest, I was still told I was just fine, because my BMI was in the middle/normal range. I was so malnourished and thin that I bruised a rib from sneezing, but I was just fine because BMI said so. If it is possible to hate a mathematical measurement, I hate BMI and attribute its influence to the disorder that I am still struggling with today.

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