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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

  • accidentalpancake
    accidentalpancake Posts: 484 Member
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    This is me at 6lbs OVER the very tip top of my "healthy" BMI range:
    s2a2necpiexc.jpg

    Being overly muscular is not a prerequisite for there being variations in the applicability of BMI. At the outer edges of height distribution, there are similar, documented issues to those that are constantly pointed out for athletes and bodybuilders.
  • stanmann571
    stanmann571 Posts: 5,727 Member
    edited November 2017
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    jdlobb wrote: »
    I'm not rehashing all of this again. it's somebody else's turn to try to get through to you.

    Except you're the one who's got it wrong.

    BF % below 26 is NORMAL/HEALTHY!!
    26 and above is Obese.

    You're confused. Just admit it.

    body%20fat%20percentage%20in%20men.jpg

    body%20fat%20percentage%20in%20women.jpg
  • jdlobb
    jdlobb Posts: 1,232 Member
    edited November 2017
    Options
    jdlobb wrote: »
    I'm not rehashing all of this again. it's somebody else's turn to try to get through to you.

    Except you're the one who's got it wrong.

    BF % below 26 is NORMAL/HEALTHY!!
    26 and above is Obese.

    You're confused. Just admit it.

    wrong.

    the study had an "ideal weight" cut off of 20.6% BF to 24.2% BF depending on age. The obese threshold was 27.5% to 31.1% depending on age.

    see Table 1

    The % incorrectly categorized was only those above the "ideal weight" threshold for their age, only those categorized as overweight or obese.

    We've been through this. You ignored it.

    I posted tables.

    edit: the tables you just posted only show 26% as ideal for someone 56 or older, and they do not come from the study you're clinging to. In fact, they're far more restrictive than the study you don't remotely understand.
  • Aaron_K123
    Aaron_K123 Posts: 7,122 Member
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    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%

    The accuracy would actually depend on the population. Presumably its more accurate in the population for which the model was initially created. I don't know what the accuracy is but I'm pretty sure it is above 50% anywhere and it probably varies population to population...I doubt it is one fixed value.
  • stanmann571
    stanmann571 Posts: 5,727 Member
    Options
    jdlobb wrote: »
    jdlobb wrote: »
    I'm not rehashing all of this again. it's somebody else's turn to try to get through to you.

    Except you're the one who's got it wrong.

    BF % below 26 is NORMAL/HEALTHY!!
    26 and above is Obese.

    You're confused. Just admit it.

    wrong.

    the study had an "ideal weight" cut off of 20.6% BF to 24.2% BF depending on age. The obese threshold was 27.5% to 31.1% depending on age.

    see Table 1

    The % incorrectly categorized was only those above the "ideal weight" threshold for their age, only those categorized as overweight or obese.

    We've been through this. You ignored it.

    I posted tables.

    edit: the tables you just posted only show 26% as ideal for someone 56 or older, and they do not come from the study you're clinging to. In fact, they're far more restrictive than the study you don't remotely understand.

    Which doesn't change the fact that 37% of women and 77% of men were miscategorized.
  • jdlobb
    jdlobb Posts: 1,232 Member
    edited November 2017
    Options
    Aaron_K123 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%

    The accuracy would actually depend on the population. Presumably its more accurate in the population for which the model was initially created. I don't know what the accuracy is but I'm pretty sure it is above 50% anywhere and it probably varies population to population...I doubt it is one fixed value.

    he's insistent that because one study found inconsistency between what BMI said was "obese" and what their cutoffs for BF% said was "obese", that BMI is thus junk. He didn't really read the study, he just pulled out a choice quote that somebody else found and posted and ran with it.

    As I repeatedly pointed out, the australian study actually makes the case that BMI is overly broad, and more people are obese than BMI says. Which is literally the exact opposite of why most people in this thread hate BMI.
  • jdlobb
    jdlobb Posts: 1,232 Member
    edited November 2017
    Options
    jdlobb wrote: »
    jdlobb wrote: »
    I'm not rehashing all of this again. it's somebody else's turn to try to get through to you.

    Except you're the one who's got it wrong.

    BF % below 26 is NORMAL/HEALTHY!!
    26 and above is Obese.

    You're confused. Just admit it.

    wrong.

    the study had an "ideal weight" cut off of 20.6% BF to 24.2% BF depending on age. The obese threshold was 27.5% to 31.1% depending on age.

    see Table 1

    The % incorrectly categorized was only those above the "ideal weight" threshold for their age, only those categorized as overweight or obese.

    We've been through this. You ignored it.

    I posted tables.

    edit: the tables you just posted only show 26% as ideal for someone 56 or older, and they do not come from the study you're clinging to. In fact, they're far more restrictive than the study you don't remotely understand.

    Which doesn't change the fact that 37% of women and 77% of men were miscategorized.

    it does. because that's not true.

    the study ONLY says that people who are overweight or overfat under either metric may be more or less overweight or overfat under the other.

    It doesn't give error rates for either ideal weight or underweight.
  • stanmann571
    stanmann571 Posts: 5,727 Member
    Options
    Aaron_K123 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%

    The accuracy would actually depend on the population. Presumably its more accurate in the population for which the model was initially created. I don't know what the accuracy is but I'm pretty sure it is above 50% anywhere and it probably varies population to population...I doubt it is one fixed value.

    It's great for populations. But wildly useless for individuals.

    Because for Populations, the 17-20% high/low for women and the 30-40% for men offset. But for individuals a 20-35% chance of getting it wrong isn't useful.
  • rokuren
    rokuren Posts: 5 Member
    edited November 2017
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    rokuren wrote: »
    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 already went with a more thorough analysis of the data. So I'll focus on something simple.

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

    What you did above? Is quite simply not how numbers work. Take women,

    17.3% of women who were identified as obese were not obese.
    19.9% of women listed as not obese but actually were.

    You can't however add the two together and claim a 37.2% error rate. Just think about it, otherwise I could say:
    While 17.3% of women who were classified as obese weren't that means 82.7% of women were identified as obese by bmi were in fact obese
    and since 19.9% of women were classified as not obese while they were it means 80.1% of women identified as not obese and weren't obese.
    82.7% + 80.1% = 168.2% accurate for women.

    BMI is clearly not 162.8% accurate for anything. You can't make the claim 37.2% incorrect for women and 77.7% incorrect for men.

    You're partly correct. The correct solution is to average the numbers...

    Which puts it at 18% for women and 36% for men ... Which is still well above the 5-10% required as above for being useful.

    No, you don't average them either. BMI has three categories normal, overweight, and obese. To calculate an actual error rate you'd need to know the number of people identified as underweight and weren't, people identified as normal and weren't, the number of people identified as overweight and weren't, and the number of people who were identified as obese and weren't.

    We literally can't make a determination on the overall accuracy of BMI based on the below two lines.
    *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%

    Edit: forgot underweight
  • Aaron_K123
    Aaron_K123 Posts: 7,122 Member
    Options
    It's great for populations. But wildly useless for individuals.

    Yeah. And? Its for population analysis. If people want to misuse it and then other people want to complain about it because it got misused I don't know how much I care about that to be honest.
  • SezxyStef
    SezxyStef Posts: 15,268 Member
    Options
    Aaron_K123 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%

    The accuracy would actually depend on the population. Presumably its more accurate in the population for which the model was initially created. I don't know what the accuracy is but I'm pretty sure it is above 50% anywhere and it probably varies population to population...I doubt it is one fixed value.

    It's great for populations. But wildly useless for individuals.

    Because for Populations, the 17-20% high/low for women and the 30-40% for men offset. But for individuals a 20-35% chance of getting it wrong isn't useful.

    I think saying it's wildly useless for individuals is a bit of an over stretch.

    and I have to say...I have no idea what my bf% is...and how do we get a reading we can count on really?

    Dexa and hydro and bod pod all have an error rate that some find to high (I think I read 5%) and none of the actual calculations work well either...the scales are crap and calipers have to much variance too...


    I think that what people need to get to is this...

    you need all the numbers to get a good snapshot of how you as an individual are doing...not just 1.

  • stanmann571
    stanmann571 Posts: 5,727 Member
    Options
    rokuren wrote: »
    rokuren wrote: »
    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 already went with a more thorough analysis of the data. So I'll focus on something simple.

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

    What you did above? Is quite simply not how numbers work. Take women,

    17.3% of women who were identified as obese were not obese.
    19.9% of women listed as not obese but actually were.

    You can't however add the two together and claim a 37.2% error rate. Just think about it, otherwise I could say:
    While 17.3% of women who were classified as obese weren't that means 82.7% of women were identified as obese by bmi were in fact obese
    and since 19.9% of women were classified as not obese while they were it means 80.1% of women identified as not obese and weren't obese.
    82.7% + 80.1% = 168.2% accurate for women.

    BMI is clearly not 162.8% accurate for anything. You can't make the claim 37.2% incorrect for women and 77.7% incorrect for men.

    You're partly correct. The correct solution is to average the numbers...

    Which puts it at 18% for women and 36% for men ... Which is still well above the 5-10% required as above for being useful.

    No, you don't average them either. BMI has three categories normal, overweight, and obese. To calculate an actual error rate you'd need to know the number of people identified as underweight and weren't, people identified as normal and weren't, the number of people identified as overweight and weren't, and the number of people who were identified as obese and weren't.

    We literally can't make a determination on the overall accuracy of BMI based on the below two lines.
    *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%

    Edit: forgot underweight

    And BODYFAT only has 3 Underweight normal and obese. Normal is often subdivided into Athletic fit and acceptable.

    But if someone is NOT OBESE per Bodyfat, then they are normal

    HTH
    HAND
  • stanmann571
    stanmann571 Posts: 5,727 Member
    Options
    Aaron_K123 wrote: »
    It's great for populations. But wildly useless for individuals.

    Yeah. And? Its for population analysis. If people want to misuse it and then other people want to complain about it because it got misused I don't know how much I care about that to be honest.

    Except it's not people misusing it. it's insurance companies and employers and doctors.