Recovering academic now in public safety. You’ll find me kibitzing on brains (my academic expertise) to critical infrastructure and resilience (current worklife). Also hockey, games, music just because.

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Cake day: July 5th, 2023

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  • BMI is used two ways; as a population tool to compare groups of people, and as a screening tool for indviduals to see if more detailed tests need to be run. I’ve given other examples of screening tests here - the sit/stand test and an alcohol screener. None of these form the basis of clinical recommendations. A positive finding is cause to ask further questions. “Oh you’re very tall ok BMI doesn’t work well then.” Or “Oh you’re muscular, that’s fine”.

    As a personal example I was a serious runner at one point in my life and my resting heart rate slipped below 40 at the doctor’s office. It set off an alarm. I confirmed that I ran about 70 miles a week and we all had a laugh about it.

    The fact that you know some edge cases doesn’t invalidate the measure. And let me point out that people have an amazingly distorted view of normal now. A 6’0" man weighing 225 lbs is obese. 225 seems like a typical weight but from a historical view that is very large. The fact that most of the North American population is overweight or obese and they don’t like to hear that.


  • You dramatically overestimate the number of people who can bench their bodyweight, forget about 2 plates. Your highschool were people in their prime, I bet those 7 did not maintain their fitness through the following 3 decades. And as I said that’s a starting point for considering whether BMI breaks down for an individual, it’s not a definitive statement.

    BMI is just a tool for assessing whether there is cause for concern. Like a screening when a physician asks how many drinks you have a week. An answer of 10 doesn’t make you an alcoholic, but they’ll ask some follow up questions.

    Similarly a BMI of 30 doesn’t produce an OMG reaction and pressure to get bariatric surgery. But it will drive a lifestyle conversation. And I can guarantee any physician who sees that result and and sees you’re built like a brick shit house will not be recommending food restriction.

    The BMI standards were established in a healthier baseline population than currently exists. The 1940s and 1950s had a higher proportion of manual labor than we have now. So those arguments fall apart.


  • It’s just fine. BMI is a proxy measure for overall health and risk of future health problems. Like any global proxy it is not a perfect fit for every situation, but it’s a reasonably accurate quick’n dirty screen to go looking for other issues. So it’s not a diagnosis in and of itself but it’s a pointer to other issues. The sit/stand test would another example of this kind of measure. It’s not measuring anything specific, but it’s highly correlated with health outcomes. BMI has the advantage of being incredibly easy to measure, and it can be done from historical records where height and weight are available.

    So there are problems with it, notably that yes muscle weighs more than fat. So yes, many bodybuilders appear as borderline obese. What this means is that there should be followup as it’s a screener. A lot of people think this affects them, but if you aren’t lifting 2/3/4, it probably doesn’t. Those heavily muscled individuals are so far out on the bell curve they don’t affect those of us in the middle 99%.

    There are other problems with it, including that it doesn’t scale well with height, so it gets wonky if you’re taller than 6’5" or so.

    Alternatives such as waist-to-hip ratio and waist circumference are better measures for individual diagnosis, but tend to not be favored in the research literature because there are not large population databases available, and historical comparisons are generally not possible.