BMI Is Bullshit, Even for the Decidedly Non-Athletic

[Content Notice for Eating Disorders]

I am a “good fatty” in the sense that I haven’t engaged in long-term unrestricted eating in many years and I make an attempt at an exercise regimen. I am a “bad fatty” in that I occasionally take breaks from my restricted eating plans, don’t engage in physical activity on a consistent basis, and am unapologetic about the fact that health can be attained even by those dubbed overweight or obese based on the BMI.

Recently, I discovered something about changes in my body composition that could be used to argue that I’m a “good fatty” — but I’m far more interested in its implications about BMI.

bar graphs showing body composition changes

In 2011, I posted online about my initial hydrostatic body composition results. I remarked on how the results showed that I’d still be overweight for my height by BMI standards even if I were to reach 20% body fat. I was told that I couldn’t expect to maintain the same level of lean muscle mass if I were to lose weight. In order words, people assured me that I’d lose lean muscle mass as well as fat as I dropped pounds, meaning that BMI would still be a valid measure and that I’d still have a high fat percentage.

As these were people who seemed to know what they were talking about, I resigned myself to a high body fat percentage no matter how much weight I lost. Three years later, I’d prove them wrong.

My weight loss has been slow at best in the years between my initial body composition measurement and my more recent one; I’ve only been highly motivated for about one of the three years.  I showed only an 8 pound loss — but gained about 2 pounds of lean muscle mass, meaning I’d lost 10 pounds of fat. This means that, if the pattern holds, my weight when I reach goal goal fat percentage will continue to place me at “overweight,” if not “obese,” according to the BMI chart.

If I were to reach 20% body fat, I’d weigh 161 pounds. At my height, 161 is on the upper end of “overweight” according to the BMI. 20% is a fairly athletic goal for a woman, though, and I am not an athlete. Let’s say I’m aiming for 25%. Barring any further gains in muscle mass, I’d weigh 172, placing me just short of the BMI definition of “obese.” If I were to gain more muscle mass, that goal weight would be even higher.

In order for me to not be overweight according to the BMI, I’d have to weigh 149. To get to that point, I would have to lose quite a lot of fat and probably at least some lean muscle mass. Not only would that be close to impossible to accomplish, it would likely be downright unhealthy for me unless I were to dedicate myself full-time to a very athletic lifestyle.

For kicks, I decided to use a BMI-based formula to calculate my body fat percentage. It decided that I must have 40% body fat, a full 6% higher than I actually have.

For me, it turns out that BMI is complete bullshit, even though I am not nor have I ever been an athlete. I wonder how many other large people, fat-shamed by their doctors and by society as a whole, are in similar situations. After all, naysayers aside, BMI has a rich history of being used as a tool by which doctors harm fat people.

a chart of my weight and other stats
(In case you’re wondering how I gained muscle mass and lost fat without much exercise at all, I can’t say that I know for sure, but I think it has something to do with the low-carb high-fat eating plan I’ve been following fairly consistently since January 2013. YMMV.)


BMI Is Bullshit, Even for the Decidedly Non-Athletic
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20 thoughts on “BMI Is Bullshit, Even for the Decidedly Non-Athletic

  1. 1

    I wrote a journal entry on the history of BMI back in the deviantart days. The short form is it’s bullshit, as you say.

    The intellectual underpinnings of BMI are ridiculous, if you look at them. Adolphe Quetelet (the guy who also helped invent “IQ”) published the “Quetelet Index” which was an ideal height/weight by gender chart that he established by the oh-so-scientific method of asking a bunch of his friends that he thought were “well formed” how much they weighed. See any possible flaws in that methodology? The Quetelet index morphed into actuarial charts used by US insurance and medical institutions in the 1950s and eventually someone curve-fit the chart to a formula, and that was how BMI came to be.

    BMI measures how well you conform with a set of 1850s Belgians.

  2. 2

    BMI is a tool that is great if you’re measuring the average weight-vs-height spread of a population. If 50% of the population has a BMI greater than 35? That’s probably a problem, especially if 30 years ago the 50% mark was 22. But that says nothing about an individual who has a BMI of 35, minus more data.

    Here’s my favorite analogy:
    Statistically speaking, the average adult woman in the US is 5’5 (165.1 cm). Does that mean that women who are significantly removed from the mean (say, a woman who is 6 feet tall) necessarily has something wrong with her? No! She might have a glandular disorder, and if she’s showing other symptoms this should be worked out. But she could just be tall.

    So a person has a BMI of 25. Is she showing symptoms (high cholesterol, for example) of ill health that can be attributed to weight? Fine! Work her up for this and suggest she lose weight. But remember that she could simply be built that way.

    1. 2.2

      Average body mass varies tremendously between populations for environmental, cultural, and biological reasons. Why are you so confident it’s problematic that 50% of the population has a BMI greater than 35? Sounds like you just pulled those numbers out of thin air. BMI was invented without any consideration of human diversity and that’s one of it’s many problems.

      By the way, high cholesterol is not actually a symptom of high weight, and also can’t necessarily be controlled by losing weight. Misinformed suggestions like these are part of the problem of how fat people are treated.

      1. Eh? I am not convinced that 50% of the population has a BMI above 35. I pulled that number out of my butt as an example of how BMI could be useful: as a way of tracking population-based changes. And yes, I am aware that high cholesterol is not necessarily caused by being over weight, or controllable by weight loss. It can be related, which is why someone with high cholesterol needs to have a workup to determine if something is going on and how the situation can be managed. Weight loss may not be part of this in any way.

        1. I know you’re not saying that’s the truth about the US population. I’m saying, in the hypothetical you gave, why WOULD it be “probably problematic” if 50% of a population had a BMI above 35? How did you make that assessment?

          And why is BMI a useful tool to track changes over time? It’s not just a unit of measurement; it comes with categories like “overweight” and “obese” that are essentially meaningless and not based on any scientific standard.

          If someone wants to use a height-weight ratio for scientific measurement purposes, that’s fine — but BMI is so soaked with bad science and fat shaming that we should really just abandon it.

          1. BMI stripped of all its extraneous crap (like “BMI > 30 = obese” and all that) is just a height/weight ratio tracker. Applied to a population, that’s fine – provided, of course, you do things like look at context (e.g. did the population-BMI rise between times A and B because in timepoint A there was a famine that stopped by timepoint B, so people weren’t starving anymore?). Outside of that, I’m not certain BMI has any utility at all.

            I think at this point that I should acknowledge that my comment was quite badly phrased, and that my point is that BMI is crap applied to individuals and potentially (with a lot of care and attention to detail and context) useful when applied to populations. A significant change in population-BMI (especially in a short time) is probably indicating something is going on that bears examining. Of course, this event could be a good thing – population-BMI increases may indicate improved nutrition, for example. This was the point of my analogy regarding heights: the mean height of a population is a rather random number that by itself is essentially meaningless, but a significant change in this mean can possibly indicate something is going on (and this can be good, bad, or a net neutral).

  3. 3

    Okay, I agree with your point that if BMI were stripped down to an arbitrary number rating based on height-weight ratio, it might be useful for tracking population trends in a preliminary investigation way, rather than making any kind of judgment about the quality of health of an individual or a population.

  4. 4

    Using BMI to determine an individual’s healthy weight is about as useful as using someone’s height to determine their sex.

    And I generally loose all respect for someone’s abilities/knowledge if they use BMI on individuals.

  5. 5

    Mileage certainly did vary. Someone I know started low carb at a similar time and in eight months managed to move one out of several cholesterol numbers a tiny notch, while doubling uric acid and not losing an ounce. Thanks for reppin’ the forces of righteousness as ever, Heina. 🙂

  6. 6

    I also seriously wish the scale would die, but then if I look at what we used before the BMI came along, it’s still kind of an improvement (at least in germany). The “scale” before was height in cm – 100, result in kg, which does work even less for smaller and taller persons than average. There’s almost no one you can apply this one too. I agree very much with you. The bias health care providers have towards perceived fatness is worrying, and we all (we nurses, the physios, the doctors) tend to judge them harsher, assume they are unhealthier, and are even harsher towards (assumed) overweight/obese women than we are towards (assumed) overweight/obese men. So is the racism though. We’re not immune against biases, but no one ever talks about this in our daily work lives. We help people after all! Aren’t we the good ones? Still people get worse outcomes because of these things.

    I do think there are negative health effects to an unhealthy lifestyle combined with massive obesity (at the point where you cannot clean yourself at the toilet, your movement is severely restricted, for example, but that’s hardly the average person we call fat) and there’s some grumpiness about increased costs with very heavy weighting people, because they need extra beds, wider wheelchairs and surgeries are harder, but well… the most ignored persons by doctors at my ward are usually older, tiny fat ladies from muslim countries. When they show symptoms of depression the reaction is usually “oh she’s just fat and lazy” and it takes much more time until various symptoms lead to a reaction, increasing the healing time and leading to complications. :/

    This has been the same at all hospitals and wards I worked so far.

    1. 6.1

      And there’s no obligation to be healthy, that’s still a personal choice, something every one of us must decide for themselves, because we do own and live with our bodies. And it’s hardly like we, the health providers, have the same reaction towards other unhealthy lifestyles.

      Smoking for example.

    1. 7.1

      Wow, that’s incredible. Thank you so much for sharing it.

      I look at the bodies of people considered “overweight” and know I would have to starve myself to get to that size. I feel confident such a system is not designed with my health in mind

      (Not saying those people must be starving themselves nor in any way shaming their bodies, just saying not all bodies can fit the mold and still be healthy)

  7. 10

    I am at an unhealthy weight now, for sure. I’ve even turned myself into a Type II diabetic. But just a few years ago I wasn’t this way at all. I had an active lifestyle. I looked good in the mirror even without clothes on. More importantly, I felt great and all of my doctors save for one said I was perfectly healthy. I was 5 feet and 9 inches tall, 180 pounds. Thin. I could run two miles even though I went for a run only a few times a year when stressed. I lived in on the tenth floor of a building with the most annoying elevators in the world so I often took the stairs. It was never a problem. But this doctor said I was obese. I was perplexed. I came home and told my girlfriend what this doctor said and she laughed. Told me I was sexy!

    Before that I had gotten ill and dropped to 165 pounds at my lowest. According to BMI that would be considered on the high end of normal but I was emaciated. You could see my ribs. Even after my illness was over I felt weak and terrible.

    So I know BMI is bullshit. This doctor who tried to tell me I was obese said I should drop 20 pounds. Even when I was sick I wasn’t 20 pounds lighter and it was awful. Again, no other doctors paid any mind to my BMI. They don’t now in spite of me being obese. Apparently most of the doctors I’ve had don’t give a shit about BMI. I would hope most feel the same way.

    Weight is a weird thing. I don’t even pay attention to it now. I just live better. I know I’m making progress because I can do more than I could six months ago. I feel a lot better. And I take photos of myself in a full length mirror from time to time. I’m not satisfied with how I look but am satisfied with my progress and I think I’ll get back to where I used to be, which is borderline obese by BMI. But with great blood work, great blood glucose levels, great blood pressure, and so on. Healthy. I’m getting there!

    People just need to pay attention to what their bodies tell them. Everybody needs exercise. Almost everybody needs to eat better than we do. There’s so much added sugar in the foods we eat. Wasn’t always this way. Gotta pay more attention to that stuff.

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