BMI

24

Replies

  • onemanpeloton
    onemanpeloton Posts: 58 Member
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    maybe that is something to take up with your medical professional then - because i know my doctor doesn't just give me advice based on BMI - she considers results of body fat assessment (done via a dexa scan and also bodpod); as well as food intake - and if she did, she wouldn't be my doctor much longer

    BMI is a statistical tool that can provide initial assessment to see whether an individual potentially falls into an increased risk category for health issues (either from being under or over weight).

    wow these replies are coming through quick, I'll try my best to keep up!

    It would seem you and I are in agreement then, BMI isn't that much of a useful tool. You need other means of testing to understand the bigger picture.
  • cdjs77
    cdjs77 Posts: 176 Member
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    maybe that is something to take up with your medical professional then - because i know my doctor doesn't just give me advice based on BMI - she considers results of body fat assessment (done via a dexa scan and also bodpod); as well as food intake - and if she did, she wouldn't be my doctor much longer

    BMI is a statistical tool that can provide initial assessment to see whether an individual potentially falls into an increased risk category for health issues (either from being under or over weight).

    wow these replies are coming through quick, I'll try my best to keep up!

    It would seem you and I are in agreement then, BMI isn't that much of a useful tool. You need other means of testing to understand the bigger picture.

    I don't think anyone is arguing anything other than that. I certainly wouldn't, as that's not what BMI was intended for other than as an initial assessment. However, most people in these forums don't provide us with the results of their full workup at the their last doctor's visit so all we have to make an assessment are height, weight age and stated activity level.

    Also, BMI, itself, isn't much of a useful tool, but it is a useful tool to make an initial assessment. It's also useful for making recommendations when you have no better information to go on.
  • onemanpeloton
    onemanpeloton Posts: 58 Member
    cdjs77 wrote: »
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.


    If by measurements you mean caliper measurements done by someone who knows what they are doing? Then probably, but measurements themselves aren't particularly accurate.

    I also think you and I have a different definition of what it means to be accurate. Individual BMI isn't meant to be a point estimate of someone's body fat percentage, it's meant as an estimate to see what category they fall into and their risks of having an unhealthy body fat percentage based on that category. If people come to MFP with a BMI of 35, it's pretty likely they are indeed obese. As for how can something with such a wide range be accurate, you do realize what it is trying to estimate right? The range of healthy body fat percentages is also wide (14% to 31% for women and 6% to 22% for men), in order to include them all there would also likely be a wide weight range. You're really asking how can such a wide range of weight be healthy and that is not a question for BMI. (Aside from that, statistical accuracy doesn't care about what you think about interval widths, if such a wide interval is accurate for a sample, it's likely mathematically accurate for the population, whether you like how the math works or not).

    18.5 is on the verge of underweight for anyone, for someone like him who regularly cycles, it's likely underweight, meaning he likely has a very low body fat percentage (especially since he is a man and likely has a lower body fat percentage than a woman at that weight). How will BMI affect his performance? It won't, but having a lower body fat percentage and trying to lose weight will, which is what BMI is estimating. If you are active and have a low BF%, you're just sacrificing muscle by losing weight, and at his height/weight, that's likely what he's doing. He's 5'9" and 66 kilos as a man, with an FTP of 220, he likely won't gain much by dieting. I say this as a 175cm (5'9") 56 kg (125lb) woman who has been this weight most of my adult life and is also an avid cyclist.

    So would you consider caliper measurements done by someone who knows what they're doing to be less accurate than BMI or more?

    I'm not sure what you mean in the first few sentences of the 2nd paragraph. Is BMI meant to determine body fat or not?

    I agree with you about extreme BMI numbers being "likely" to correlate with obesity, but that can still be better understood by talking about the persons body composition rather than blindly applying a number and therefore a category to them.

    I still don't understand the link youre making with cycling and BMI. Why does him being someone "who regularly cycles" have anything to do with being "likely underweight"? If we trust BMI then hes either underweight or he isnt, regardless of whether he cycles or sits on the couch all day.

    You said originally that his BMI will probably negatively affect his performance. Now you say it won't......

    Why would having a lower body fat % negatively affect his performance if he lowers that percentage further? He's specifically interested in climbing hills, where a good power to weight ratio is essential. If that fat isn't assisting his power up the hills then it is hindering his power/weight ratio and slowing him down. I won't comment on whether thats a healthy choice, but I'm not sure how its possible to claim that it will negatively affect his performance.

    Lastly, I'm not sure why you're telling me your statistics. What difference does that make to this discussion?

  • collectingblues
    collectingblues Posts: 2,541 Member
    mitch16 wrote: »
    mitch16 wrote: »
    Yes, body composition is important but there are very few athletic persuits that require one to be outside a 'normal' BMI.

    And the usual complaint is that athletes are on the high side of BMI/overweight/obese if you don't take into account composition.

    Outside of woman's gymnastics and maybe figure skating I can't think of any other athletic sports where the low end of the BMI scale is an athletic advantage.

    And if you look at the stats for most of the Olympic female gymnasts, thanks to the muscle, most of them are actually in the 20-22 BMI ballpark.

    Many of them are tiptoeing around the bottom end according to this... https://www.topendsports.com/events/summer/science/gymnastics-all-round.htm

    Interesting. The 2016 and 2012 classes -- admittedly, I was looking much more at 2016 -- were closer to the 19s/20s/21s.
  • onemanpeloton
    onemanpeloton Posts: 58 Member
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    maybe that is something to take up with your medical professional then - because i know my doctor doesn't just give me advice based on BMI - she considers results of body fat assessment (done via a dexa scan and also bodpod); as well as food intake - and if she did, she wouldn't be my doctor much longer

    BMI is a statistical tool that can provide initial assessment to see whether an individual potentially falls into an increased risk category for health issues (either from being under or over weight).

    wow these replies are coming through quick, I'll try my best to keep up!

    It would seem you and I are in agreement then, BMI isn't that much of a useful tool. You need other means of testing to understand the bigger picture.

    you're talking about about throwing the baby out with the bathwater because it doesn't fit your perception of useful

    I'm not sure that's the case. Your doctor gives you advice based on BMI as well as other means of assessment. The instances I'm referring to treat BMI as a single wonder number on it's own with no other questions asked
  • onemanpeloton
    onemanpeloton Posts: 58 Member
    mitch16 wrote: »
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    Except mfp really isn't specific advice to individuals based on their personal circumstances... It's an internet forum with a wide range of users, with a wide range of personal experiences, and a wide range of capabilities (intellectual or otherwise). Speaking in the generalities of BMI is enough for plenty of the users here--these are people who ask if raspberry ketones or the HCG diet will work. People who have a good idea of where they want to go and what they want to do, health- and weight-wise, are working with trainers, dietitians, etc. outside of mfp and aren't on here asking random internet strangers for advice on BMI.

    Sorry, I missed your message.

    In large part, I agree. Which is why I still concede that I understand how BMI can be rolled out as a very general rule of thumb for a massive audience with a huge range of variation.

    However, the minute a single person asks a question and a single person responds, surely that response can be slightly tailored to the individual. If it wasnt then why not close the forum and just redirect everyone to a bmi calculator?
  • deannalfisher
    deannalfisher Posts: 5,600 Member
    cdjs77 wrote: »
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    maybe that is something to take up with your medical professional then - because i know my doctor doesn't just give me advice based on BMI - she considers results of body fat assessment (done via a dexa scan and also bodpod); as well as food intake - and if she did, she wouldn't be my doctor much longer

    BMI is a statistical tool that can provide initial assessment to see whether an individual potentially falls into an increased risk category for health issues (either from being under or over weight).

    wow these replies are coming through quick, I'll try my best to keep up!

    It would seem you and I are in agreement then, BMI isn't that much of a useful tool. You need other means of testing to understand the bigger picture.

    I don't think anyone is arguing anything other than that. I certainly wouldn't, as that's not what BMI was intended for other than as an initial assessment. However, most people in these forums don't provide us with the results of their full workup at the their last doctor's visit so all we have to make an assessment are height, weight age and stated activity level.

    Also, BMI, itself, isn't much of a useful tool, but it is a useful tool to make an initial assessment. It's also useful for making recommendations when you have no better information to go on.

    That's a really interesting point. In my experience in reading these forums it tends to be the people replying who say "whats your height and weight, we can work out your BMI" .....rather than saying "tell us some more useful information so that we can properly help you".

    But if it isnt that useful then why use it as an initial assessment? Why not get straight in to the details rather than starting to give advice based on some assumption gained from a tool that isnt useful, as you said

    because very few people on the forum likely have immediate access to a facility where body fat or VO2Max or BMR etc - can be assessed - so asking for BMI is an initial look-see and then further recommendations can be made

    There are plenty of examples of what I've said, you will come across them pretty quickly. I can barely keep up with the speed of these comments, let alone search the forum for all past threads I've read too.

    My point still remains that the "initial look see" can still be wrong, so it seems useless to start with it at all.

    It seems we have probably reached the point where we have to agree to disagree. Hopefully this link sums up some of my thoughts (about BMI, not shape index, I don't know anything about that)

    https://shapescale.com/blog/health/why-bmi-is-wrong-and-shape-index-is-telling-the-truth/

    according to this - my "new" BMI is higher than my actual BMI...so tell me how its a better measurement
  • cdjs77
    cdjs77 Posts: 176 Member
    cdjs77 wrote: »
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.


    If by measurements you mean caliper measurements done by someone who knows what they are doing? Then probably, but measurements themselves aren't particularly accurate.

    I also think you and I have a different definition of what it means to be accurate. Individual BMI isn't meant to be a point estimate of someone's body fat percentage, it's meant as an estimate to see what category they fall into and their risks of having an unhealthy body fat percentage based on that category. If people come to MFP with a BMI of 35, it's pretty likely they are indeed obese. As for how can something with such a wide range be accurate, you do realize what it is trying to estimate right? The range of healthy body fat percentages is also wide (14% to 31% for women and 6% to 22% for men), in order to include them all there would also likely be a wide weight range. You're really asking how can such a wide range of weight be healthy and that is not a question for BMI. (Aside from that, statistical accuracy doesn't care about what you think about interval widths, if such a wide interval is accurate for a sample, it's likely mathematically accurate for the population, whether you like how the math works or not).

    18.5 is on the verge of underweight for anyone, for someone like him who regularly cycles, it's likely underweight, meaning he likely has a very low body fat percentage (especially since he is a man and likely has a lower body fat percentage than a woman at that weight). How will BMI affect his performance? It won't, but having a lower body fat percentage and trying to lose weight will, which is what BMI is estimating. If you are active and have a low BF%, you're just sacrificing muscle by losing weight, and at his height/weight, that's likely what he's doing. He's 5'9" and 66 kilos as a man, with an FTP of 220, he likely won't gain much by dieting. I say this as a 175cm (5'9") 56 kg (125lb) woman who has been this weight most of my adult life and is also an avid cyclist.

    So would you consider caliper measurements done by someone who knows what they're doing to be less accurate than BMI or more?

    I'm not sure what you mean in the first few sentences of the 2nd paragraph. Is BMI meant to determine body fat or not?

    I agree with you about extreme BMI numbers being "likely" to correlate with obesity, but that can still be better understood by talking about the persons body composition rather than blindly applying a number and therefore a category to them.

    I still don't understand the link youre making with cycling and BMI. Why does him being someone "who regularly cycles" have anything to do with being "likely underweight"? If we trust BMI then hes either underweight or he isnt, regardless of whether he cycles or sits on the couch all day.

    You said originally that his BMI will probably negatively affect his performance. Now you say it won't......

    Why would having a lower body fat % negatively affect his performance if he lowers that percentage further? He's specifically interested in climbing hills, where a good power to weight ratio is essential. If that fat isn't assisting his power up the hills then it is hindering his power/weight ratio and slowing him down. I won't comment on whether thats a healthy choice, but I'm not sure how its possible to claim that it will negatively affect his performance.

    Lastly, I'm not sure why you're telling me your statistics. What difference does that make to this discussion?

    Sorry, English isn't my native language so perhaps the language in my post was confusing. Yes, I think caliper measurements done by a "professional" are probably more accurate at assessing BF% than BMI (but I also don't know whether this is true, I have never looked up the study of accuracy of calipers).

    BMI, itself, the number, does nothing more than put you into a category, it's the categories which are useful. I do not think BMI, itself, estimates BF% as a point estimate (by point estimate I mean it is not accurate to say a BMI of X equals X% bodyfat, point estimates are never accurate and no statistician would claim such), BMI can, however, make an estimate of whether one is over- or underfat.
    I still don't understand the link youre making with cycling and BMI. Why does him being someone "who regularly cycles" have anything to do with being "likely underweight"? If we trust BMI then hes either underweight or he isnt, regardless of whether he cycles or sits on the couch all day.

    I say likely because that is how statistics work. BMI is a statistical estimate. It does nothing more than give "likelihoods" and those likelihoods vary with different lifestyle factors (because the underlying population changes, if you want to know the mathematical reason). If we trust BMI then we can only say likelihood because that is all it tells us: likelihoods and risks.
    18.5 is the cutoff point for a healthy BMI, taken from the whole population, with no other information, one could only say he was likely on the verge of underweight (because BMI is a likelihood estimation). If we know that he is an active cyclist, the underlying population changes. We are now not looking at BMI for the average population, we are looking at BMI for active cyclists. This distribution will look different. In this distribution, the cutoff BMI for being underfat will likely be higher.

    As for BMI negatively affecting his performance, I must have worded it improperly or you misunderstood what I meant, I think having a low BF% and trying to lose weight will negatively affect his performance. I do not think BMI, itself, will negatively affect his performance, it is nothing more than an inferential statistic. If he has a low BF%, it will be hard for him to lose any significant amount of weight without also losing a lot of muscle. If he has a BF% of 20, then he can surely go for it and probably gain some power out of it. However, his w/kg is probably equivalent to a cat 4 racer, he could gain a lot more from decent training before he could gain power by losing weight. He isn't at the point yet where he can only gain power by dropping weight.
    Lastly, I'm not sure why you're telling me your statistics. What difference does that make to this discussion?

    Because I'm a cyclist at his desired weight/height, so I know how it affects at least my own performance. I also want to point out that I am not one of those MFPers who thinks anyone under a BMI of 20 is anorexic, as many people here seem to think.
  • onemanpeloton
    onemanpeloton Posts: 58 Member
    cdjs77 wrote: »
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    maybe that is something to take up with your medical professional then - because i know my doctor doesn't just give me advice based on BMI - she considers results of body fat assessment (done via a dexa scan and also bodpod); as well as food intake - and if she did, she wouldn't be my doctor much longer

    BMI is a statistical tool that can provide initial assessment to see whether an individual potentially falls into an increased risk category for health issues (either from being under or over weight).

    wow these replies are coming through quick, I'll try my best to keep up!

    It would seem you and I are in agreement then, BMI isn't that much of a useful tool. You need other means of testing to understand the bigger picture.

    I don't think anyone is arguing anything other than that. I certainly wouldn't, as that's not what BMI was intended for other than as an initial assessment. However, most people in these forums don't provide us with the results of their full workup at the their last doctor's visit so all we have to make an assessment are height, weight age and stated activity level.

    Also, BMI, itself, isn't much of a useful tool, but it is a useful tool to make an initial assessment. It's also useful for making recommendations when you have no better information to go on.

    That's a really interesting point. In my experience in reading these forums it tends to be the people replying who say "whats your height and weight, we can work out your BMI" .....rather than saying "tell us some more useful information so that we can properly help you".

    But if it isnt that useful then why use it as an initial assessment? Why not get straight in to the details rather than starting to give advice based on some assumption gained from a tool that isnt useful, as you said

    because very few people on the forum likely have immediate access to a facility where body fat or VO2Max or BMR etc - can be assessed - so asking for BMI is an initial look-see and then further recommendations can be made

    There are plenty of examples of what I've said, you will come across them pretty quickly. I can barely keep up with the speed of these comments, let alone search the forum for all past threads I've read too.

    My point still remains that the "initial look see" can still be wrong, so it seems useless to start with it at all.

    It seems we have probably reached the point where we have to agree to disagree. Hopefully this link sums up some of my thoughts (about BMI, not shape index, I don't know anything about that)

    https://shapescale.com/blog/health/why-bmi-is-wrong-and-shape-index-is-telling-the-truth/

    according to this - my "new" BMI is higher than my actual BMI...so tell me how its a better measurement

    I'd encourage you, again, to read my post properly. I clearly stated that the information on that site summed up my thoughts on why BMI was such a limited tool, and was not a reflection of my thoughts on shape index, of which I have no knowledge
  • onemanpeloton
    onemanpeloton Posts: 58 Member
    cdjs77 wrote: »
    cdjs77 wrote: »
    ceiswyn wrote: »

    not exclusively although that thread does have elements of what I'm talking about, yes

    I don't think that thread is the hill to die on. Regardless of the error rate involved with BMI, it's probably pretty accurate in predicting whether or not one is underweight if they are highly active. A BMI of 18.5 for a very active cyclist is likely underweight and will probably negatively affect performance (and I say that as a cyclist with a BMI of 18.5).

    As for other mentions of BMI, it's not inaccurate enough that it should be disposed of completely, and for most people coming to this website, it's probably a good thing to keep an eye on. It also wouldn't hurt to choose goal weights for most people here based on BMI, especially if they don't have another way of accurately measuring their body fat.

    I think we've already concluded that it wasn't one thread in isolation, so no ones dying on any hills.

    How can something with such a broad range of acceptable measurements be classed as "pretty accurate"? Using myself as the example again, I wouldnt consider a 25% range of variability to be "pretty accurate".

    I'm intrigued about the relationship between BMI and being active. Why is 18.5 (a supposedly healthy level of BMI) unhealthy for a cyclist and how would it negatively affect performance?

    For weight loss, it seems to me that taking measurements of key areas of the body (as MFP allows you to do) would give you a better indication of body composition vs weight.

    do you understand statistics at all and standard deviations? 25% of the population will fit into typically 1 standard deviation of the avg population - which is why they pick that range

    I do understand statistics. Do you understand the art of reading a post properly and understanding it?

    I'm talking about giving specific advice to individuals based on their personal circumstances. It's foolish to apply an average to an individual. Imagine what the world would be like if everyone actually had 2.4 children......

    maybe that is something to take up with your medical professional then - because i know my doctor doesn't just give me advice based on BMI - she considers results of body fat assessment (done via a dexa scan and also bodpod); as well as food intake - and if she did, she wouldn't be my doctor much longer

    BMI is a statistical tool that can provide initial assessment to see whether an individual potentially falls into an increased risk category for health issues (either from being under or over weight).

    wow these replies are coming through quick, I'll try my best to keep up!

    It would seem you and I are in agreement then, BMI isn't that much of a useful tool. You need other means of testing to understand the bigger picture.

    I don't think anyone is arguing anything other than that. I certainly wouldn't, as that's not what BMI was intended for other than as an initial assessment. However, most people in these forums don't provide us with the results of their full workup at the their last doctor's visit so all we have to make an assessment are height, weight age and stated activity level.

    Also, BMI, itself, isn't much of a useful tool, but it is a useful tool to make an initial assessment. It's also useful for making recommendations when you have no better information to go on.

    That's a really interesting point. In my experience in reading these forums it tends to be the people replying who say "whats your height and weight, we can work out your BMI" .....rather than saying "tell us some more useful information so that we can properly help you".

    But if it isnt that useful then why use it as an initial assessment? Why not get straight in to the details rather than starting to give advice based on some assumption gained from a tool that isnt useful, as you said

    because very few people on the forum likely have immediate access to a facility where body fat or VO2Max or BMR etc - can be assessed - so asking for BMI is an initial look-see and then further recommendations can be made

    There are plenty of examples of what I've said, you will come across them pretty quickly. I can barely keep up with the speed of these comments, let alone search the forum for all past threads I've read too.

    My point still remains that the "initial look see" can still be wrong, so it seems useless to start with it at all.

    It seems we have probably reached the point where we have to agree to disagree. Hopefully this link sums up some of my thoughts (about BMI, not shape index, I don't know anything about that)

    https://shapescale.com/blog/health/why-bmi-is-wrong-and-shape-index-is-telling-the-truth/

    according to this - my "new" BMI is higher than my actual BMI...so tell me how its a better measurement

    I've no expertise in this but a study published in the Journal of Translational Medicine concluded it was a "much better indicator of mortality risk". Maybe that's a good place to start