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BMI isn't a reliable indicator to gauge obesity. For example, Tom Brady at 6' 4" and 225 lbs is considered overweight, which is obviously not the case. That be

BMI isn't a reliable indicator to gauge obesity. For example, Tom Brady at 6' 4" and 225 lbs is considered overweight, which is obviously not the case. That being said, as an American, it really did shock me how fit the majority of people were in Italy when I visited there for the first time last year. This New England Journal of Medicine chart really does a good job of showing that America has gotten heavier over the years: https://www.nejm.org/na101/home/literatum/publisher/mms/journals/content/nejm/2019/nejm_2019.381.issue-25/nejmsa1909301/20191213-01/images/img_xlarge/nejmsa1909301_f1.jpeg https://www.nejm.org/na101/home/literatum/publisher/mms/jour... Source: https://www.nejm.org/doi/full/10.1056/NEJMsa1909301 https://www.nejm.org/doi/full/10.1056/NEJMsa1909301

cma 6y ago
For a population study BMI is fine, elite NFL players aren't going to move the needle.
diarmuidc 6y ago
A professional athlete doesn't need a simple metric to understand if he's at his ideal weight. It's part of his job. The general public do need a simple metric which covers 95% of the population. BMI is that.
sangli 6y ago
BMI isn't a reliable indicator go gauge obesity FOR EVERY SINGLE PERSON. I would think most of us agree that the people like Tom Brady, Dwyane Johnson (the rock), or competitive body builders would be extreme ends of this scale. For average people BMI is a reliable indicator.
- mirekrusin 6y ago
  That’s because muscles are heavier than fat, right?
  - pmalynin 6y ago
    They are more dense, yes.
  - rhino369 6y ago
    It also doesn't a good job of modeling ideal weight for short or tall people. BMI models a human in only two dimensions.
  - treis 6y ago
    BMI assumes you have an average amount of muscle. Any weight above that is assumed to be fat. So for someone like the Rock it treats a lot of muscle as though it were fat.
Buttons840 6y ago
It goes the other way too. You might have a BMI in the "healthy" range, but actually have an unhealthy amount of body fat [0]. Of course, nobody puts themselves in this category. [0]: https://en.wikipedia.org/wiki/Body_mass_index#/media/File:Correlation_between_BMI_and_Percent_Body_Fat_for_Men_in_NCHS'_NHANES_1994_Data.PNG https://en.wikipedia.org/wiki/Body_mass_index#/media/File:Co...
- t-writescode 6y ago
  That tends to be called skinny fat, and it's the worst feeling and takes a whole different kind of work to escape. A lot of non-cardio gym time and protein eating.
mirekrusin 6y ago
Same Paris, metro gates would simply filter out three quarters of population if installed in US.
bambataa 6y ago
Why, how many Americans have the figure of Tom Brady? Is that number big enough to have a meaningful impact on average BMIs? I don’t understand why everyone is so quite to dismiss BMI based on edge cases, especially when the finding is backed up by your other evidence.
- lumost 6y ago
  It makes it so that people don't have a strong sense of what a healthy version of themselves is, and can assert that they must be healthy "as they are". I've found Body fat % to be a more useful number, it's easy to understand what you'd look like with 10% less body fat - and you won't see many/any athletes with 30%+ body fat. When I first started tracking this I was shocked by the initial number (35%) and managed to work it down to 17% over time, my total weight didn't change by more than 5%.
  - mmcconnell1618 6y ago
    I think body fat percentage is a reasonable metric but even that isn't absolute. For example, studies on Sumo wrestlers in Japan found that while they had lots of fat, they didn't suffer from the adverse affects of obesity while they maintained their active workout schedule. Once they left the career and stopped exercising, the obesity related health problems showed up. Exercise and activity play a significant role in overall health, not just fat percentage and weight. https://www.businessinsider.com/sumo-wrestlers-obesity-diet-calories-exercise-symptoms-2019-3#:~:text=CT%20scans%20reveal%20that%20sumo,much%20visceral%20fat%20at%20all.&text=That's%20why%20scientists%20think%20sumo,%2C%20heart%20attack%2C%20and%20stroke https://www.businessinsider.com/sumo-wrestlers-obesity-diet-....
- sergiotapia 6y ago
  Because it forces people to confront the reality of their obesity and how out of shape they are.
forrestthewoods 6y ago
Define reliable. If a metric had 95% accuracy would that qualify as reliable? I would certainly say so. Especially if the 5% outliers are not random but in fact an extremely obvious edge case? I do not know how “reliable” BMI is. But elite athletes represent an exceedingly small percent of the population. My intuition is that BMI is a pretty darn good first approximation. And instances where it’s not good there is supporting evidence.
tasty_freeze 6y ago
Every time BMI is mentioned someone has to come up with an example of a body builder or fit athlete who has a high BMI. Yes, everyone realizes this already, and nobody who is in that position is going to be mislead into thinking they are obese. Sure, it would be great if everyone could do a caliper test or a water displacement test, but that isn't ever going to happen, and BMI is a trivial and good enough place to start. Because being overweight/obese is normalized because it is seen everywhere, there are tens of millions of people who have no idea they are at an unhealthy weight ... they rightly think they look like everyone else. The BMI is a an easy metric to get people to evaluate if they need to do something about it.
- kbenson 6y ago
  > Yes, everyone realizes this already, and nobody who is in that position is going to be mislead into thinking they are obese. No, but someone who works out the numbers and realizes that the BMI doesn't match them well, or their circumstances well, realizes it calls the study and what it represents into question. Using controversial metrics because they are easily available is counter-productive in the long run, because once people realize you were misrepresenting your credibility is lost. At best it's lazy. Right now I'm obese. In high school according to the BMI I was almost half-way through overweight edging towards obese, and that was with very little fat, a very active lifestyle, and a visible six-pack. How do I consider studies that make claims about percentages of people that fit into those categories? As extremely ambiguous in what they are actually indicating. Do Americans have a problem with weight? I think so. Does using false numbers to overestimate the problem help? I don't think so, especially when people realize the metrics leave a lot to be desired.
  - viraptor 6y ago
    The measurements don't have to be precise to show a trend, relation, or infer a number of valid results. If someone calls the study into question based on using imperfect methods, rather than using those methods incorrectly... That's their opinion, but it's not useful.
    - 6y ago
lldbg 6y ago
Literally the exception that confirms the rule.
JackMorgan 6y ago
No athlete I know bothers with BMI - it's meant for non-athletes. Likewise athletes often accept that bodyweight corresponds almost directly with lifting potential, but obviously we know that's it's only true for athletes, otherwise every obese person would be setting world record deadlifts.
syshum 6y ago
BMI is a poor indicator of Individuals Health BMI is a good metric for POPULATION level studies, infact it was designed explicit for that purpose So me calculating my individual BMI then making health judgments solely on that number is stupid. However A person calculating the BMI of all persons in a Population then using those numbers to judge to overall condition of the population is valid
Sodman 6y ago
Professional athletes, along with most people who work out 4+ days / week, have their own more advanced/expensive ways of determining their own personal weight and judging where they should be, factoring other measurements like muscle mass percentage. They also make up a very small percentage of the US population. For everyone else, it's a decent approximation of weight. As anecdata - I'm on the opposite end of the physical activity spectrum to Tom Brady, I'm also 6'4" and the heaviest I've been is about ~210 lbs. I was definitely starting to feel "a bit too big" at that, and would confidently say I'd feel overweight at 225 lbs, so the scale doesn't feel massively miscalibrated to me.

cma 6y ago

For a population study BMI is fine, elite NFL players aren't going to move the needle.

diarmuidc 6y ago

A professional athlete doesn't need a simple metric to understand if he's at his ideal weight. It's part of his job. The general public do need a simple metric which covers 95% of the population. BMI is that.

sangli 6y ago

BMI isn't a reliable indicator go gauge obesity FOR EVERY SINGLE PERSON. I would think most of us agree that the people like Tom Brady, Dwyane Johnson (the rock), or competitive body builders would be extreme ends of this scale. For average people BMI is a reliable indicator.

mirekrusin 6y ago
That’s because muscles are heavier than fat, right?
- pmalynin 6y ago
  They are more dense, yes.
- rhino369 6y ago
  It also doesn't a good job of modeling ideal weight for short or tall people. BMI models a human in only two dimensions.
- treis 6y ago
  BMI assumes you have an average amount of muscle. Any weight above that is assumed to be fat. So for someone like the Rock it treats a lot of muscle as though it were fat.

Buttons840 6y ago

It goes the other way too. You might have a BMI in the "healthy" range, but actually have an unhealthy amount of body fat [0]. Of course, nobody puts themselves in this category. [0]: https://en.wikipedia.org/wiki/Body_mass_index#/media/File:Correlation_between_BMI_and_Percent_Body_Fat_for_Men_in_NCHS'_NHANES_1994_Data.PNG https://en.wikipedia.org/wiki/Body_mass_index#/media/File:Co...

t-writescode 6y ago
That tends to be called skinny fat, and it's the worst feeling and takes a whole different kind of work to escape. A lot of non-cardio gym time and protein eating.

mirekrusin 6y ago

Same Paris, metro gates would simply filter out three quarters of population if installed in US.

bambataa 6y ago

Why, how many Americans have the figure of Tom Brady? Is that number big enough to have a meaningful impact on average BMIs? I don’t understand why everyone is so quite to dismiss BMI based on edge cases, especially when the finding is backed up by your other evidence.

lumost 6y ago
It makes it so that people don't have a strong sense of what a healthy version of themselves is, and can assert that they must be healthy "as they are". I've found Body fat % to be a more useful number, it's easy to understand what you'd look like with 10% less body fat - and you won't see many/any athletes with 30%+ body fat. When I first started tracking this I was shocked by the initial number (35%) and managed to work it down to 17% over time, my total weight didn't change by more than 5%.
- mmcconnell1618 6y ago
  I think body fat percentage is a reasonable metric but even that isn't absolute. For example, studies on Sumo wrestlers in Japan found that while they had lots of fat, they didn't suffer from the adverse affects of obesity while they maintained their active workout schedule. Once they left the career and stopped exercising, the obesity related health problems showed up. Exercise and activity play a significant role in overall health, not just fat percentage and weight. https://www.businessinsider.com/sumo-wrestlers-obesity-diet-calories-exercise-symptoms-2019-3#:~:text=CT%20scans%20reveal%20that%20sumo,much%20visceral%20fat%20at%20all.&text=That's%20why%20scientists%20think%20sumo,%2C%20heart%20attack%2C%20and%20stroke https://www.businessinsider.com/sumo-wrestlers-obesity-diet-....
sergiotapia 6y ago
Because it forces people to confront the reality of their obesity and how out of shape they are.

forrestthewoods 6y ago

Define reliable. If a metric had 95% accuracy would that qualify as reliable? I would certainly say so. Especially if the 5% outliers are not random but in fact an extremely obvious edge case? I do not know how “reliable” BMI is. But elite athletes represent an exceedingly small percent of the population. My intuition is that BMI is a pretty darn good first approximation. And instances where it’s not good there is supporting evidence.

tasty_freeze 6y ago

Every time BMI is mentioned someone has to come up with an example of a body builder or fit athlete who has a high BMI. Yes, everyone realizes this already, and nobody who is in that position is going to be mislead into thinking they are obese. Sure, it would be great if everyone could do a caliper test or a water displacement test, but that isn't ever going to happen, and BMI is a trivial and good enough place to start. Because being overweight/obese is normalized because it is seen everywhere, there are tens of millions of people who have no idea they are at an unhealthy weight ... they rightly think they look like everyone else. The BMI is a an easy metric to get people to evaluate if they need to do something about it.

kbenson 6y ago
> Yes, everyone realizes this already, and nobody who is in that position is going to be mislead into thinking they are obese. No, but someone who works out the numbers and realizes that the BMI doesn't match them well, or their circumstances well, realizes it calls the study and what it represents into question. Using controversial metrics because they are easily available is counter-productive in the long run, because once people realize you were misrepresenting your credibility is lost. At best it's lazy. Right now I'm obese. In high school according to the BMI I was almost half-way through overweight edging towards obese, and that was with very little fat, a very active lifestyle, and a visible six-pack. How do I consider studies that make claims about percentages of people that fit into those categories? As extremely ambiguous in what they are actually indicating. Do Americans have a problem with weight? I think so. Does using false numbers to overestimate the problem help? I don't think so, especially when people realize the metrics leave a lot to be desired.
- viraptor 6y ago
  The measurements don't have to be precise to show a trend, relation, or infer a number of valid results. If someone calls the study into question based on using imperfect methods, rather than using those methods incorrectly... That's their opinion, but it's not useful.
  - 6y ago

lldbg 6y ago

Literally the exception that confirms the rule.

JackMorgan 6y ago

No athlete I know bothers with BMI - it's meant for non-athletes. Likewise athletes often accept that bodyweight corresponds almost directly with lifting potential, but obviously we know that's it's only true for athletes, otherwise every obese person would be setting world record deadlifts.

syshum 6y ago

BMI is a poor indicator of Individuals Health BMI is a good metric for POPULATION level studies, infact it was designed explicit for that purpose So me calculating my individual BMI then making health judgments solely on that number is stupid. However A person calculating the BMI of all persons in a Population then using those numbers to judge to overall condition of the population is valid

Sodman 6y ago

Professional athletes, along with most people who work out 4+ days / week, have their own more advanced/expensive ways of determining their own personal weight and judging where they should be, factoring other measurements like muscle mass percentage. They also make up a very small percentage of the US population. For everyone else, it's a decent approximation of weight. As anecdata - I'm on the opposite end of the physical activity spectrum to Tom Brady, I'm also 6'4" and the heaviest I've been is about ~210 lbs. I was definitely starting to feel "a bit too big" at that, and would confidently say I'd feel overweight at 225 lbs, so the scale doesn't feel massively miscalibrated to me.