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My favourite comment on this is the following joke exchange: Doctor: Your BMI is high I'd like you make some dietary adjustments. Patient: BMI doesn't measure

by s_dev 2y ago

My favourite comment on this is the following joke exchange: Doctor: Your BMI is high I'd like you make some dietary adjustments. Patient: BMI doesn't measure fat accurately for example professional Rugby players are marked as obese but aren't. Doctor: Are you a Rugby player? Patrient: No. It's a good guideline. Don't let edge cases control your perception and let professionals do their thing with the tools they have -- they're aware of limitations that's why their professionals.

eagerpace 2y ago
I've done a couple DEXA scans recently and they have in fact confirmed that the BMI calculation for me is spot on.
- impute 2y ago
  I also just did a DEXA scan last week and the calculator is within ~2% so pretty good considering it's free and takes 1 minute.
kelipso 2y ago
There are plenty of people who do weightlifting or have high muscle density. Probably more than 10% of people and certainly not edge cases. Doctors are basically taught like undergrads are taught, not much critical thinking involved, they just recite whatever is in the relevant document they are supposed to recite from.
- impute 2y ago
  I really doubt more than 10% of people do weightlifting and have high muscle density. It's likely closer to 0.1% which is why BMI is a good guideline over a group.
  - skrtskrt 2y ago
    being within an "ideal" or "average" bodyfat range will easily put you as overweight on BMI. it's a useless statistic.
- fkyoureadthedoc 2y ago
  Doctors are much more likely to let obesity slide than they are to nag you about BMI when you're clearly in shape in my experience.
  - cjbgkagh 2y ago
    The problem is not so much what the doctor will tell people in person but that these same people will end up in stats and should be separated into their own category. Having a high BMI and that excludes strength trainers would make high BMI stats worse than it is already.
    - TheCoelacanth 2y ago
      Those people do skew the stats by a bit, but they are outnumbered by the people who are "skinny fat", i.e. people who are very sedentary and who have high body fat but still have normal BMIs due to having very low lean body mass.
WaitWaitWha 2y ago
> It's a good guideline. 100% accurate. Caveat Emptor - the world does not understand even the smallest nuance that needs to take into consideration - in this case "guideline". For example, the US DoD used BMI (DoDI 1308.03) to disqualify a friend of mine from joining. his actual body fat by DEXA? 7%, he was just short and very fit.
arcticbull 2y ago
While that joke is accurate (although some football players are also obese [1] depending on their position -- Aaron Gibson was 400lbs), BMI was never meant to be applied to individuals. It was designed to be applied to populations. It does a good job of that. Also note that guidelines have historically been created against a very limited selection of race and have not appropriately adjusted for height (although BMI 2.0 corrects the height issues). If we're just relying on the professional's opinion then they don't really need the BMI, right. They can just look at you and go "huh, you're looking a little thicc today." BMI is a good tool for population health, a bad tool for individual health, and if it just so happens to correlate to your thiccness then you probably already know that. I agree with parent that body composition analysis via DEXA or air displacement plethysmography is a far better metric. I have no doubt that a carpenter can bang a nail in with a screwdriver 90% of the time, that's why they're professionals after all, but when I see it, I can't help but think "there's gotta be a better way mate." [1] https://www.nytimes.com/2019/01/17/sports/football/the-nfls-obesity-scourge.html https://www.nytimes.com/2019/01/17/sports/football/the-nfls-...
- HeatrayEnjoyer 2y ago
  Why would race matter? Melanin doesn't effect fat comp... does it?
  - lostlogin 2y ago
    Body composition varies by race. https://pmc.ncbi.nlm.nih.gov/articles/PMC4968570/ https://pmc.ncbi.nlm.nih.gov/articles/PMC4968570/ https://www.sciencedirect.com/science/article/pii/S0002916523071782 https://www.sciencedirect.com/science/article/pii/S000291652...
  - fjdjshsh 2y ago
    They don't need to be causally connected, just be correlated.
  - meiraleal 2y ago
    > Why would race matter? Because social matter
Retr0id 2y ago
GP is not questioning the usefulness of body fat percentage as a statistic (that's its own question), but the crude method of measurement. It says mine is 1.6%, which I'd say is at least 5% out.
skrtskrt 2y ago
It is bad all around, the inaccuracies start waaaay before you get to something you could call an "edge case". I'm 5'11, 180 lb male, that counts as overweight. I'm 18% bodyfat. You wouldn't even note me as being particularly athletic looking if you walked by, I'm right in the middle of the bell curve for "guy who works out sometimes". There's no way it should be flagging someone like me as overweight.
- anon84873628 2y ago
  Two months ago I was in a similar situation as you. I'm a few inches shorter but had the same body fat percentage, and my history of lifting still showed. I went to a new primary care doctor and who said I was a bit overweight. I had the same initial response of "oh come on!" and general exasperation with the state of medical care. The thing is, he really wasn't wrong. From an epidemiology perspective it is simply better to be leaner if possible. The fact that I didn't "look fat" isn't really relevant; I was still carrying excess adipose tissue. I already had a DEXA scan booked and was planning to do a cut before that exam. I lost about 10 pounds over the next 8 weeks through basic caloric deficit and moderate exercise. It wasn't exactly fun but it also wasn't that difficult, and the results were far more impactful than I expected. Yes, I looked noticably lean with more muscle definition. I also went down a pants size and felt better in general. My blood work, especially lipid panel, was better than ever. All this is to say that, while BMI charts certainly have flaws, and all individuals are different, most of us can still improve our health and longevity prospects by shedding excess fat. And that probably is leaner than we might expect.
teeray 2y ago
If we're going to use imperfect measures for the average Joe, then wouldn't a cheap bioelectrical impedence body fat test be at least a better approximation than jamming height and weight into a formula?

by s_dev 2y ago

eagerpace 2y ago

I've done a couple DEXA scans recently and they have in fact confirmed that the BMI calculation for me is spot on.

impute 2y ago
I also just did a DEXA scan last week and the calculator is within ~2% so pretty good considering it's free and takes 1 minute.

kelipso 2y ago

There are plenty of people who do weightlifting or have high muscle density. Probably more than 10% of people and certainly not edge cases. Doctors are basically taught like undergrads are taught, not much critical thinking involved, they just recite whatever is in the relevant document they are supposed to recite from.

impute 2y ago
I really doubt more than 10% of people do weightlifting and have high muscle density. It's likely closer to 0.1% which is why BMI is a good guideline over a group.
- skrtskrt 2y ago
  being within an "ideal" or "average" bodyfat range will easily put you as overweight on BMI. it's a useless statistic.
fkyoureadthedoc 2y ago
Doctors are much more likely to let obesity slide than they are to nag you about BMI when you're clearly in shape in my experience.
- cjbgkagh 2y ago
  The problem is not so much what the doctor will tell people in person but that these same people will end up in stats and should be separated into their own category. Having a high BMI and that excludes strength trainers would make high BMI stats worse than it is already.
  - TheCoelacanth 2y ago
    Those people do skew the stats by a bit, but they are outnumbered by the people who are "skinny fat", i.e. people who are very sedentary and who have high body fat but still have normal BMIs due to having very low lean body mass.

WaitWaitWha 2y ago

> It's a good guideline. 100% accurate. Caveat Emptor - the world does not understand even the smallest nuance that needs to take into consideration - in this case "guideline". For example, the US DoD used BMI (DoDI 1308.03) to disqualify a friend of mine from joining. his actual body fat by DEXA? 7%, he was just short and very fit.

arcticbull 2y ago

While that joke is accurate (although some football players are also obese [1] depending on their position -- Aaron Gibson was 400lbs), BMI was never meant to be applied to individuals. It was designed to be applied to populations. It does a good job of that. Also note that guidelines have historically been created against a very limited selection of race and have not appropriately adjusted for height (although BMI 2.0 corrects the height issues). If we're just relying on the professional's opinion then they don't really need the BMI, right. They can just look at you and go "huh, you're looking a little thicc today." BMI is a good tool for population health, a bad tool for individual health, and if it just so happens to correlate to your thiccness then you probably already know that. I agree with parent that body composition analysis via DEXA or air displacement plethysmography is a far better metric. I have no doubt that a carpenter can bang a nail in with a screwdriver 90% of the time, that's why they're professionals after all, but when I see it, I can't help but think "there's gotta be a better way mate." [1] https://www.nytimes.com/2019/01/17/sports/football/the-nfls-obesity-scourge.html https://www.nytimes.com/2019/01/17/sports/football/the-nfls-...

HeatrayEnjoyer 2y ago
Why would race matter? Melanin doesn't effect fat comp... does it?
- lostlogin 2y ago
  Body composition varies by race. https://pmc.ncbi.nlm.nih.gov/articles/PMC4968570/ https://pmc.ncbi.nlm.nih.gov/articles/PMC4968570/ https://www.sciencedirect.com/science/article/pii/S0002916523071782 https://www.sciencedirect.com/science/article/pii/S000291652...
- fjdjshsh 2y ago
  They don't need to be causally connected, just be correlated.
- meiraleal 2y ago
  > Why would race matter? Because social matter

Retr0id 2y ago

GP is not questioning the usefulness of body fat percentage as a statistic (that's its own question), but the crude method of measurement. It says mine is 1.6%, which I'd say is at least 5% out.

skrtskrt 2y ago

It is bad all around, the inaccuracies start waaaay before you get to something you could call an "edge case". I'm 5'11, 180 lb male, that counts as overweight. I'm 18% bodyfat. You wouldn't even note me as being particularly athletic looking if you walked by, I'm right in the middle of the bell curve for "guy who works out sometimes". There's no way it should be flagging someone like me as overweight.

anon84873628 2y ago
Two months ago I was in a similar situation as you. I'm a few inches shorter but had the same body fat percentage, and my history of lifting still showed. I went to a new primary care doctor and who said I was a bit overweight. I had the same initial response of "oh come on!" and general exasperation with the state of medical care. The thing is, he really wasn't wrong. From an epidemiology perspective it is simply better to be leaner if possible. The fact that I didn't "look fat" isn't really relevant; I was still carrying excess adipose tissue. I already had a DEXA scan booked and was planning to do a cut before that exam. I lost about 10 pounds over the next 8 weeks through basic caloric deficit and moderate exercise. It wasn't exactly fun but it also wasn't that difficult, and the results were far more impactful than I expected. Yes, I looked noticably lean with more muscle definition. I also went down a pants size and felt better in general. My blood work, especially lipid panel, was better than ever. All this is to say that, while BMI charts certainly have flaws, and all individuals are different, most of us can still improve our health and longevity prospects by shedding excess fat. And that probably is leaner than we might expect.

teeray 2y ago

If we're going to use imperfect measures for the average Joe, then wouldn't a cheap bioelectrical impedence body fat test be at least a better approximation than jamming height and weight into a formula?