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Is every single body in the world intended to be within the so-called healthy BMI range?

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Replies

  • NorthCascades
    NorthCascades Posts: 10,970 Member
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    It's not a measure of health. If the world used BMI to decide how many fingers people have, jewelry stores would sell a lot of rings.
  • jdlobb
    jdlobb Posts: 1,232 Member
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    Arnold and The Rock are not outliers and do not disprove the rule. They have worked hard to engage in behavior that would yield a high BMI and low BF%, intentionally.

    People need to stop using them as examples of "outliers."

    tomteboda is an outlier, a true outlier
  • lemurcat12
    lemurcat12 Posts: 30,886 Member
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    Does not fit everyone does not mean "dated."

    No one claims it fits everyone (or at least very few (if any, I'm not sure) people of those involved in the current discussion). Nor is the proper use of BMI to trump/outweigh other better measures.
  • lemurcat12
    lemurcat12 Posts: 30,886 Member
    Aaron_K123 wrote: »
    Lets pretend there is a rule that is quick to implement and fits 95% of use cases. You have two options.

    Option 1: acknowledge that such a rule has uses
    Option 2: Point out the 5% of the time that the rule does not yield the correct answer and mock said rule as being useless.

    So what do you think. Do you think such a rule has no functional use? That being correct 95% of the time for very little effort of input has no value? Let me put it in another way then....

    On a case by case basis if you are dealing with one piece of data (an individual) then maybe you would choose to implement the rule that works 99.9% of the time instead but takes much more effort and time to implement. That would be rational, I think that would probably be the right call. If, however, you are dealing with a massive dataset it would probably make a lot more sense to use the rule that is right 95% of the time but takes a fraction of the time to implement.

    BMI is like the 95% rule. It is used for analysis of populations (large datasets). If applied to an individual by an individual there are certainly better methods one could choose than BMI. That doesn't make BMI "wrong" or "useless".

    I mean, people get that right? That isn't a hard concept to understand is it?

    You wouldn't think so.
  • jdlobb
    jdlobb Posts: 1,232 Member
    Aaron_K123 wrote: »
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    That...is not...what BMI...is for. If you use a hammer to try to cut down a tree yeah you might think the hammer is a useless tool but maybe, just maybe, you just aren't using the hammer for its intended purpose. Maybe there is nothing wrong with a hammer as a tool.

    BMI isn't for individuals, it is for populations. It is a statistical measure. If you attempt to use a tool for the wrong thing of course it doesn't work very well.

    ok, let's be a little clear on something.

    As a tool it predicts that 95% of people in a population would be approximately within the normal BMI range under normal conditions, with no extenuating factors. Not that any particular percentage of people WILL be in that range.

    Likewise, on an individual level, it predicts that there is a 95% probability that any particular individual in a population would be in the normal BMI range baring external conditions or other factors.

    Your average person would have a normal BMI if they didn't lead a sedentary lifestyle and each more calories than their body needs.

    Likewise, your average person would have a normal BMI if they didn't spend hours a day in the gym cultivating extra-ordinary muscle mass.

    If you, as an individual, do not have a "normal" BMI, then the next step is to take additional factors into consideration. If they are negative, not enough exercise and too much food, then they should be eliminated for the good of your health. If they are positive, lots of exercise and proper nutrition, then they should be encouraged. If they are outside of your control, disease or disorder, then they should be treated. But BMI provides a reasonable baseline estimate from which to start, and to identify if there are mitigating factors that need to be addressed (for good or bad.)
  • jdlobb
    jdlobb Posts: 1,232 Member
    Aaron_K123 wrote: »
    jdlobb wrote: »
    Aaron_K123 wrote: »
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    That...is not...what BMI...is for. If you use a hammer to try to cut down a tree yeah you might think the hammer is a useless tool but maybe, just maybe, you just aren't using the hammer for its intended purpose. Maybe there is nothing wrong with a hammer as a tool.

    BMI isn't for individuals, it is for populations. It is a statistical measure. If you attempt to use a tool for the wrong thing of course it doesn't work very well.

    ok, let's be a little clear on something.

    As a tool it predicts that 95% of people in a population would be approximately within the normal BMI range under normal conditions, with no extenuating factors. Not that any particular percentage of people WILL be in that range.

    Likewise, on an individual level, it predicts that there is a 95% probability that any particular individual in a population would be in the normal BMI range baring external conditions or other factors.

    Your average person would have a normal BMI if they didn't lead a sedentary lifestyle and each more calories than their body needs.

    Likewise, your average person would have a normal BMI if they didn't spend hours a day in the gym cultivating extra-ordinary muscle mass.

    If you, as an individual, do not have a "normal" BMI, then the next step is to take additional factors into consideration. If they are negative, not enough exercise and too much food, then they should be eliminated for the good of your health. If they are positive, lots of exercise and proper nutrition, then they should be encouraged. If they are outside of your control, disease or disorder, then they should be treated. But BMI provides a reasonable baseline estimate from which to start, and to identify if there are mitigating factors that need to be addressed (for good or bad.)

    I was taking into account the idea of applying BMI as a metric of health (yes I understand that is not exactly what it is for but that is how people are using it). What I was saying was that for a given population 95% of the time if you apply BMI as a means to determine if someone is obese or not the answer you get will be right (BMI is 28, person is predicted to be obese...person is obese) while 5% it will be wrong (BMI is 28, person is predicted to be obese...person is not obese). One could argue that that is just a misapplication of BMI in the first place but I'm trying to speak to the context of its use within this debate.

    So as a "rule for determining whether a person is obese" maybe it has a 95% accuracy (I made up that number, just giving it as an example).

    BMI is not a normalized distribution. What is considered a "normal BMI" is not the peak of a bell curve or something it is based on studies of BMI compared to measures of body compisition. You could have a population where the majority of people do not have a "normal" BMI.

    i think we're in agreement
  • Aaron_K123
    Aaron_K123 Posts: 7,122 Member
    jdlobb wrote: »
    Aaron_K123 wrote: »
    jdlobb wrote: »
    Aaron_K123 wrote: »
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    That...is not...what BMI...is for. If you use a hammer to try to cut down a tree yeah you might think the hammer is a useless tool but maybe, just maybe, you just aren't using the hammer for its intended purpose. Maybe there is nothing wrong with a hammer as a tool.

    BMI isn't for individuals, it is for populations. It is a statistical measure. If you attempt to use a tool for the wrong thing of course it doesn't work very well.

    ok, let's be a little clear on something.

    As a tool it predicts that 95% of people in a population would be approximately within the normal BMI range under normal conditions, with no extenuating factors. Not that any particular percentage of people WILL be in that range.

    Likewise, on an individual level, it predicts that there is a 95% probability that any particular individual in a population would be in the normal BMI range baring external conditions or other factors.

    Your average person would have a normal BMI if they didn't lead a sedentary lifestyle and each more calories than their body needs.

    Likewise, your average person would have a normal BMI if they didn't spend hours a day in the gym cultivating extra-ordinary muscle mass.

    If you, as an individual, do not have a "normal" BMI, then the next step is to take additional factors into consideration. If they are negative, not enough exercise and too much food, then they should be eliminated for the good of your health. If they are positive, lots of exercise and proper nutrition, then they should be encouraged. If they are outside of your control, disease or disorder, then they should be treated. But BMI provides a reasonable baseline estimate from which to start, and to identify if there are mitigating factors that need to be addressed (for good or bad.)

    I was taking into account the idea of applying BMI as a metric of health (yes I understand that is not exactly what it is for but that is how people are using it). What I was saying was that for a given population 95% of the time if you apply BMI as a means to determine if someone is obese or not the answer you get will be right (BMI is 28, person is predicted to be obese...person is obese) while 5% it will be wrong (BMI is 28, person is predicted to be obese...person is not obese). One could argue that that is just a misapplication of BMI in the first place but I'm trying to speak to the context of its use within this debate.

    So as a "rule for determining whether a person is obese" maybe it has a 95% accuracy (I made up that number, just giving it as an example).

    BMI is not a normalized distribution. What is considered a "normal BMI" is not the peak of a bell curve or something it is based on studies of BMI compared to measures of body compisition. You could have a population where the majority of people do not have a "normal" BMI.

    i think we're in agreement

    Yeah probably, I was just clarifying not wagging my finger at you
  • stanmann571
    stanmann571 Posts: 5,728 Member
    Aaron_K123 wrote: »
    jdlobb wrote: »
    Aaron_K123 wrote: »
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    That...is not...what BMI...is for. If you use a hammer to try to cut down a tree yeah you might think the hammer is a useless tool but maybe, just maybe, you just aren't using the hammer for its intended purpose. Maybe there is nothing wrong with a hammer as a tool.

    BMI isn't for individuals, it is for populations. It is a statistical measure. If you attempt to use a tool for the wrong thing of course it doesn't work very well.

    ok, let's be a little clear on something.

    As a tool it predicts that 95% of people in a population would be approximately within the normal BMI range under normal conditions, with no extenuating factors. Not that any particular percentage of people WILL be in that range.

    Likewise, on an individual level, it predicts that there is a 95% probability that any particular individual in a population would be in the normal BMI range baring external conditions or other factors.

    Your average person would have a normal BMI if they didn't lead a sedentary lifestyle and each more calories than their body needs.

    Likewise, your average person would have a normal BMI if they didn't spend hours a day in the gym cultivating extra-ordinary muscle mass.

    If you, as an individual, do not have a "normal" BMI, then the next step is to take additional factors into consideration. If they are negative, not enough exercise and too much food, then they should be eliminated for the good of your health. If they are positive, lots of exercise and proper nutrition, then they should be encouraged. If they are outside of your control, disease or disorder, then they should be treated. But BMI provides a reasonable baseline estimate from which to start, and to identify if there are mitigating factors that need to be addressed (for good or bad.)

    I was taking into account the idea of applying BMI as a metric of health (yes I understand that is not exactly what it is for but that is how people are using it). What I was saying was that for a given population 95% of the time if you apply BMI as a means to determine if someone is obese or not the answer you get will be right (BMI is 28, person is predicted to be obese...person is obese) while 5% it will be wrong (BMI is 28, person is predicted to be obese...person is not obese). One could argue that that is just a misapplication of BMI in the first place but I'm trying to speak to the context of its use within this debate.

    So as a "rule for determining whether a person is obese" maybe it has a 95% accuracy (I made up that number, just giving it as an example). Maybe a DEXA scan has a 99.9% accuracy. If you are dealing with an individual and have both options then yeah go with the DEXA. If you are dealing with a large population and want to know what percentage is obese you aren't going to DEXA scan the entire populace so go with BMI.

    BMI is not a normalized distribution. What is considered a "normal BMI" is not the peak of a bell curve or something it is based on studies of BMI compared to measures of body compisition. You could have a population where the majority of people do not have a "normal" BMI.

    Except the actual accuracy isn't even close to 95%... it's closer to 70%
  • jdlobb
    jdlobb Posts: 1,232 Member
    Aaron_K123 wrote: »
    jdlobb wrote: »
    Aaron_K123 wrote: »
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    That...is not...what BMI...is for. If you use a hammer to try to cut down a tree yeah you might think the hammer is a useless tool but maybe, just maybe, you just aren't using the hammer for its intended purpose. Maybe there is nothing wrong with a hammer as a tool.

    BMI isn't for individuals, it is for populations. It is a statistical measure. If you attempt to use a tool for the wrong thing of course it doesn't work very well.

    ok, let's be a little clear on something.

    As a tool it predicts that 95% of people in a population would be approximately within the normal BMI range under normal conditions, with no extenuating factors. Not that any particular percentage of people WILL be in that range.

    Likewise, on an individual level, it predicts that there is a 95% probability that any particular individual in a population would be in the normal BMI range baring external conditions or other factors.

    Your average person would have a normal BMI if they didn't lead a sedentary lifestyle and each more calories than their body needs.

    Likewise, your average person would have a normal BMI if they didn't spend hours a day in the gym cultivating extra-ordinary muscle mass.

    If you, as an individual, do not have a "normal" BMI, then the next step is to take additional factors into consideration. If they are negative, not enough exercise and too much food, then they should be eliminated for the good of your health. If they are positive, lots of exercise and proper nutrition, then they should be encouraged. If they are outside of your control, disease or disorder, then they should be treated. But BMI provides a reasonable baseline estimate from which to start, and to identify if there are mitigating factors that need to be addressed (for good or bad.)

    I was taking into account the idea of applying BMI as a metric of health (yes I understand that is not exactly what it is for but that is how people are using it). What I was saying was that for a given population 95% of the time if you apply BMI as a means to determine if someone is obese or not the answer you get will be right (BMI is 28, person is predicted to be obese...person is obese) while 5% it will be wrong (BMI is 28, person is predicted to be obese...person is not obese). One could argue that that is just a misapplication of BMI in the first place but I'm trying to speak to the context of its use within this debate.

    So as a "rule for determining whether a person is obese" maybe it has a 95% accuracy (I made up that number, just giving it as an example). Maybe a DEXA scan has a 99.9% accuracy. If you are dealing with an individual and have both options then yeah go with the DEXA. If you are dealing with a large population and want to know what percentage is obese you aren't going to DEXA scan the entire populace so go with BMI.

    BMI is not a normalized distribution. What is considered a "normal BMI" is not the peak of a bell curve or something it is based on studies of BMI compared to measures of body compisition. You could have a population where the majority of people do not have a "normal" BMI.

    Except the actual accuracy isn't even close to 95%... it's closer to 70%

    citation needed
  • stanmann571
    stanmann571 Posts: 5,728 Member
    jdlobb wrote: »
    Aaron_K123 wrote: »
    jdlobb wrote: »
    Aaron_K123 wrote: »
    If the world went by BMI

    Arnold Schwarzenegger in his prime would be considered super morbidly obese as would Dwayne 'the rock' Johnson, it's a dated measurement of health.

    That...is not...what BMI...is for. If you use a hammer to try to cut down a tree yeah you might think the hammer is a useless tool but maybe, just maybe, you just aren't using the hammer for its intended purpose. Maybe there is nothing wrong with a hammer as a tool.

    BMI isn't for individuals, it is for populations. It is a statistical measure. If you attempt to use a tool for the wrong thing of course it doesn't work very well.

    ok, let's be a little clear on something.

    As a tool it predicts that 95% of people in a population would be approximately within the normal BMI range under normal conditions, with no extenuating factors. Not that any particular percentage of people WILL be in that range.

    Likewise, on an individual level, it predicts that there is a 95% probability that any particular individual in a population would be in the normal BMI range baring external conditions or other factors.

    Your average person would have a normal BMI if they didn't lead a sedentary lifestyle and each more calories than their body needs.

    Likewise, your average person would have a normal BMI if they didn't spend hours a day in the gym cultivating extra-ordinary muscle mass.

    If you, as an individual, do not have a "normal" BMI, then the next step is to take additional factors into consideration. If they are negative, not enough exercise and too much food, then they should be eliminated for the good of your health. If they are positive, lots of exercise and proper nutrition, then they should be encouraged. If they are outside of your control, disease or disorder, then they should be treated. But BMI provides a reasonable baseline estimate from which to start, and to identify if there are mitigating factors that need to be addressed (for good or bad.)

    I was taking into account the idea of applying BMI as a metric of health (yes I understand that is not exactly what it is for but that is how people are using it). What I was saying was that for a given population 95% of the time if you apply BMI as a means to determine if someone is obese or not the answer you get will be right (BMI is 28, person is predicted to be obese...person is obese) while 5% it will be wrong (BMI is 28, person is predicted to be obese...person is not obese). One could argue that that is just a misapplication of BMI in the first place but I'm trying to speak to the context of its use within this debate.

    So as a "rule for determining whether a person is obese" maybe it has a 95% accuracy (I made up that number, just giving it as an example). Maybe a DEXA scan has a 99.9% accuracy. If you are dealing with an individual and have both options then yeah go with the DEXA. If you are dealing with a large population and want to know what percentage is obese you aren't going to DEXA scan the entire populace so go with BMI.

    BMI is not a normalized distribution. What is considered a "normal BMI" is not the peak of a bell curve or something it is based on studies of BMI compared to measures of body compisition. You could have a population where the majority of people do not have a "normal" BMI.

    Except the actual accuracy isn't even close to 95%... it's closer to 70%

    citation needed

    Done already, as you well know.

  • stevencloser
    stevencloser Posts: 8,911 Member
    lemurcat12 wrote: »
    Aaron_K123 wrote: »
    Lets pretend there is a rule that is quick to implement and fits 95% of use cases. You have two options.

    Option 1: acknowledge that such a rule has uses
    Option 2: Point out the 5% of the time that the rule does not yield the correct answer and mock said rule as being useless.

    So what do you think. Do you think such a rule has no functional use? That being correct 95% of the time for very little effort of input has no value? Let me put it in another way then....

    On a case by case basis if you are dealing with one piece of data (an individual) then maybe you would choose to implement the rule that works 99.9% of the time instead but takes much more effort and time to implement. That would be rational, I think that would probably be the right call. If, however, you are dealing with a massive dataset it would probably make a lot more sense to use the rule that is right 95% of the time but takes a fraction of the time to implement.

    BMI is like the 95% rule. It is used for analysis of populations (large datasets). If applied to an individual by an individual there are certainly better methods one could choose than BMI. That doesn't make BMI "wrong" or "useless".

    I mean, people get that right? That isn't a hard concept to understand is it?

    You wouldn't think so.

    You know how in maths there's the associative law?

    (a + b) + c = a + (b + c), same for *.

    I just learned a bit ago in one of my classes that that rule does not work inside of computers because of the way decimal numbers are made and kept inside of it. The rule only works about 60-70% of the time, in the other cases at some point in the decimals there's going to be a deviation between the two results.
    Doesn't make the rule useless.
  • stanmann571
    stanmann571 Posts: 5,728 Member
    edited November 2017
    lemurcat12 wrote: »
    Here's one good comparison of BF% and BMI (given that the purpose of BMI is to act as a proxy for BF%): https://bmcobes.biomedcentral.com/articles/10.1186/2052-9538-1-9

    Key findings (note, this is for white people in Australia, there are likely race-based differences):

    *17.3% of women and 31.6% of men identified as obese according to BMI were not, based on BF%.
    *19.9% of women and 46.1% of men who were NOT obese by BMI actually were by BF%

    *BMI particularly underestimates adiposity in elderly men (aged 70 years and older), but also in young men (aged 20–29 years).

    That's different from another such study I recall seeing in the past, where it was much more likely to mischaracterize women as not obese when they were than obese when they were not. There was more mischaracterization for the overweight category in that one (this one focused on obesity measures only).

    17.3+19.9=37.2% incorrect for women
    31.6+46.1=77.7% incorrect for men

    I know it's confusing, because the BMI chart includes a "overweight category" and the BF chart does not.


  • jdlobb
    jdlobb Posts: 1,232 Member
    I'm not rehashing all of this again. it's somebody else's turn to try to get through to you.