4 ms·

I'm really not a fan of BMI being the determining factor in obesity. At 27 BMI, I'm apparently 3 BMI away from being considered obese. As a naturally large, f

by tfb 14y ago

I'm really not a fan of BMI being the determining factor in obesity. At 27 BMI, I'm apparently 3 BMI away from being considered obese. As a naturally large, fairly muscular 24 year old german/irish man, I'm 6 foot 1 and weigh 205 lbs, but you can see my abs and I'm in relatively good physical condition. Is my definition of obese wrong? I always thought obese meant someone with at least a few dozen lbs of excess fat.

streptomycin 14y ago
Invent a way of easily measuring body fat percentage, and we can do away with BMI. Until then, muscular people can simply ignore these things. BMI works well enough for the rest of the population (the vast majority of the world). If anything, normal people have the opposite problem you do. BMI tends to underestimate obesity in the general population. http://www.cnn.com/2012/04/03/health/obesity-rates-maybe-worse/index.html http://www.cnn.com/2012/04/03/health/obesity-rates-maybe-wor...
- evilmushroom 14y ago
  There are techniques for doing this. I weight lift... a lot. So BMI is utterly useless for me (as you said)
  - streptomycin 14y ago
    No, there aren't. BMI can be calculated by anyone in about 2 seconds without taking any measurements they don't already know. Body fat percentage can't. And while BMI may be useless to you, it's reasonably useful for the vast majority of people in the world.
    - gaius 14y ago
      I sure wouldn't want my insurance premiums to be calculated on my BMI.
      - streptomycin 14y ago
        Ok? What's your point?
      - geebee 14y ago
        Unfortunately, they are. However, I don't think most insurance companies put you into a lower category based on BMI alone until you hit 27 or so. It's still possible to be at a healthy body fat percentage and have a BMI of 27 or higher, but obviously it's not as likely as it is at the cutoff of 25. Overall, I think BMI is probably a pretty good overall metric, just not a good diagnosis for an individual. For instance, a physician might notice that a patient has a BMI above 25, but then see that waist to height ratio or a bf measurement looks very favorable. From a broad numbers perspective, I think BMI is probably very useful - for instance, if you notice that a higher percentage of a population has a BMI in excess of 27 than in previous years, you can safely estimate that the population is becoming increasingly overweight. I suspect that the situation where people have high bmi's with low body fat is limited to a small number of athletes who are not typical of the population at large.
      - deleted 14y ago
        [deleted]
    - dredmorbius 14y ago
      There are tons of things which can be calculated easily and simply, which are simply wrong or utterly useless. Palmistry, astrological signs, numerology, stock charting, biorhythms, dowsing, etc., etc. Simply because a measurement is fast, simple, and gives some arbitrary numerical precision doesn't make it useful. It's also got to, you know, like, correspond to the stuff it's supposed to be measuring. Which it doesn't. Official discussion of BMI actually admits this. The panel did not search for evidence to prove that measures of body composition or metabolic rate are useful tools. http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm
      - deleted 14y ago
        [deleted]
      - streptomycin 14y ago
        The absence of evidence is not the evidence of absence. Especially when the absence of evidence is simply a report that is not looking for what you're looking for. Either way, BMI clearly has some use. Or do you think this chart is completely random and devoid of correlation? http://upload.wikimedia.org/wikipedia/commons/b/b7/Correlation_between_BMI_and_Percent_Body_Fat_for_Men_in_NCHS%27_NHANES_1994_Data.PNG http://upload.wikimedia.org/wikipedia/commons/b/b7/Correlati... Do you think the ordering of countries on the BBC link is purely random and has nothing to do with how many fat people are in each country?
        dredmorbius 14y ago
        That chart is largely irrelevant to the discussion in several ways. Your question is specious. It shows population correlations. In a general population, where a range of bodytypes may be assumed, there will be a correlation between BMI and body fat percentage. There's relatively little argument over that, though as I mentioned above, the actual utility of BMI for epidemiological / population studies is being question. - The question isn't "is there a correlation?", but "is the correlation between BMI and body fat stronger or weaker than for other estimators of body fat?". For which you'd want to look at the r^2, RSS (residual sum of squares), and perhaps plotted residuals to determine the appropriateness of the model, in comparison with other estimators: waist circumference, height/waist ratio (most people also have a pretty good idea of their waist size), circumference and caliper estimators, etc. - To paraphrase Donald Rumsfeld, in epidemiological population studies, you conduct research with the data you have, not with the data you want. Height and weight are widely collected and reported, even from sources such as DMV files (though they may also be wildly inaccurate). For large-scale or national studies, this makes for large datasets. The relevance and usefulness of the data may not be as high as, say, DEXA analysis, or even waist to height ratio (http://www.webmd.com/heart-disease/news/20050606/waist-height-ratio-may-show-heart-disease-risk http://www.webmd.com/heart-disease/news/20050606/waist-heigh...), but it's there. And for at least some purposes, useful. Extending the use to individuals, where in most settings (home, gym, doctor's office, clinic, health fair), availability of necessary measurement tools (tape measure, calipers, even the wildly inaccurate handheld electronic bioimpedance monitors) is readily facilitated, there's really no call to rely on BMI. - The problem with BMI is that it's essentially saying "if you fit our model of body fat relative to height and weight, then here is where you fall on our model of obesity". Again, for a general population this relationship holds reasonably well, but for an individual, where the question specifically is "what is my body fat percentage", BMI is the wrong tool for the job. It fails notably for specific populations of interest -- it will consistently underreport obesity in less-healthy populations, and overreports obesity in more-healthy populations. It can also result in nonsensical intervention recommendations: most unfit people will benefit by efforts to increase lean muscle mass, despite the fact that for those with lower BMIs this will decrease their putative health score by increasing overall body mass. I suspect this is among the reasons strength training is under-recommended for increasing fitness (most literature addresses "diet" and "exercise" generally, but makes little or no distinction between cardio and strength training, or focuses virtually exclusively on cardio).
- dredmorbius 14y ago
  A simple waist circumference measurement is more accurate than BMI at making individual assessments of obesity (> 40" ~ 100cm is bad). A set of 3-4 tape measurements (height, neck, abdomen for men; height, neck, waist, hips for women) will give a reasonable estimate of body fat. Equipment cost, about $5. http://www.linear-software.com/online.html http://www.linear-software.com/online.html Your observation of the weakness of BMI is that it tends to misreport true body fat percentage both ways. I'd hardly call that an advantage of BMI. Note that since official US government policy defines obesity in terms of BMI, technically, BMI doesn't misreport obesity. What it does is fail to correspond to true body fat percentage in any meaningful way.
  - streptomycin 14y ago
    My point is that BMI is ridiculously easy for nearly everyone to measure. Your point is that a better measurement can be made if everyone goes out and buys some new thing and takes some new measurement. That seems to be in agreement with my point. > since official US government policy defines obesity in terms of BMI, technically, BMI doesn't misreport obesity The US government defining something doesn't make it true. >What it does is fail to correspond to true body fat percentage in any meaningful way. It is very meaningful. It's much better than a random guess.
    - dredmorbius 14y ago
      How are you positing people measure their weight and height without, you know, like, a scale, and, um, a tape measure? As many people in the fitness/bodybuilding field will tell you, eyeball estimates of bodyfat are in fact pretty bloody accurate. If you're interested in equipment costs, I could look up eyeballs on Amazon as I did for tape measures.
      - streptomycin 14y ago
        Most people know their weight and height already. And again, I agree that there are more accurate measurements, but they are all significantly more complicated. This time you are suggesting training people to visually estimate body fat percentage. That could work. But it's a heck of a lot more complicated than telling someone to type their height and weight into a website.
- graeme 14y ago
  This is true, but it's impact is overestimate. I used to hover near the 25 level for my BMI. I was muscular, so I thought it was silly. But I've not lost 6 pounds while gaining strength. I can see my abs. Turns out I was 12 pounds over my high school weight. I'd now need ~8 pounds of extra muscle to become "overweight". That's a lot. I think it's hard to go over BMI based on muscle alone. You may have less of a problem is you're BMI 25 and muscular, but you still probably could stand to lose some fat.
- krschultz 14y ago
  Well, I have a scale at home that does Body Fat %, and it is reasonably accurate. (It is consistent day to day, compared to a doctor's office one its off by maybe 1%). I believe it was $50. There are several on Amazon for that price and lower. If a regular scale is $20, and one that measures body fat is $40, then I don't think it's a big deal. I personally watch the body fat % now rather than weight.

by tfb 14y ago

streptomycin 14y ago

Invent a way of easily measuring body fat percentage, and we can do away with BMI. Until then, muscular people can simply ignore these things. BMI works well enough for the rest of the population (the vast majority of the world). If anything, normal people have the opposite problem you do. BMI tends to underestimate obesity in the general population. http://www.cnn.com/2012/04/03/health/obesity-rates-maybe-worse/index.html http://www.cnn.com/2012/04/03/health/obesity-rates-maybe-wor...

evilmushroom 14y ago
There are techniques for doing this. I weight lift... a lot. So BMI is utterly useless for me (as you said)
- streptomycin 14y ago
  No, there aren't. BMI can be calculated by anyone in about 2 seconds without taking any measurements they don't already know. Body fat percentage can't. And while BMI may be useless to you, it's reasonably useful for the vast majority of people in the world.
  - gaius 14y ago
    I sure wouldn't want my insurance premiums to be calculated on my BMI.
    - streptomycin 14y ago
      Ok? What's your point?
    - geebee 14y ago
      Unfortunately, they are. However, I don't think most insurance companies put you into a lower category based on BMI alone until you hit 27 or so. It's still possible to be at a healthy body fat percentage and have a BMI of 27 or higher, but obviously it's not as likely as it is at the cutoff of 25. Overall, I think BMI is probably a pretty good overall metric, just not a good diagnosis for an individual. For instance, a physician might notice that a patient has a BMI above 25, but then see that waist to height ratio or a bf measurement looks very favorable. From a broad numbers perspective, I think BMI is probably very useful - for instance, if you notice that a higher percentage of a population has a BMI in excess of 27 than in previous years, you can safely estimate that the population is becoming increasingly overweight. I suspect that the situation where people have high bmi's with low body fat is limited to a small number of athletes who are not typical of the population at large.
    - deleted 14y ago
      [deleted]
  - dredmorbius 14y ago
    There are tons of things which can be calculated easily and simply, which are simply wrong or utterly useless. Palmistry, astrological signs, numerology, stock charting, biorhythms, dowsing, etc., etc. Simply because a measurement is fast, simple, and gives some arbitrary numerical precision doesn't make it useful. It's also got to, you know, like, correspond to the stuff it's supposed to be measuring. Which it doesn't. Official discussion of BMI actually admits this. The panel did not search for evidence to prove that measures of body composition or metabolic rate are useful tools. http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm
    - deleted 14y ago
      [deleted]
    - streptomycin 14y ago
      The absence of evidence is not the evidence of absence. Especially when the absence of evidence is simply a report that is not looking for what you're looking for. Either way, BMI clearly has some use. Or do you think this chart is completely random and devoid of correlation? http://upload.wikimedia.org/wikipedia/commons/b/b7/Correlation_between_BMI_and_Percent_Body_Fat_for_Men_in_NCHS%27_NHANES_1994_Data.PNG http://upload.wikimedia.org/wikipedia/commons/b/b7/Correlati... Do you think the ordering of countries on the BBC link is purely random and has nothing to do with how many fat people are in each country?
      - dredmorbius 14y ago
        That chart is largely irrelevant to the discussion in several ways. Your question is specious. It shows population correlations. In a general population, where a range of bodytypes may be assumed, there will be a correlation between BMI and body fat percentage. There's relatively little argument over that, though as I mentioned above, the actual utility of BMI for epidemiological / population studies is being question. - The question isn't "is there a correlation?", but "is the correlation between BMI and body fat stronger or weaker than for other estimators of body fat?". For which you'd want to look at the r^2, RSS (residual sum of squares), and perhaps plotted residuals to determine the appropriateness of the model, in comparison with other estimators: waist circumference, height/waist ratio (most people also have a pretty good idea of their waist size), circumference and caliper estimators, etc. - To paraphrase Donald Rumsfeld, in epidemiological population studies, you conduct research with the data you have, not with the data you want. Height and weight are widely collected and reported, even from sources such as DMV files (though they may also be wildly inaccurate). For large-scale or national studies, this makes for large datasets. The relevance and usefulness of the data may not be as high as, say, DEXA analysis, or even waist to height ratio (http://www.webmd.com/heart-disease/news/20050606/waist-height-ratio-may-show-heart-disease-risk http://www.webmd.com/heart-disease/news/20050606/waist-heigh...), but it's there. And for at least some purposes, useful. Extending the use to individuals, where in most settings (home, gym, doctor's office, clinic, health fair), availability of necessary measurement tools (tape measure, calipers, even the wildly inaccurate handheld electronic bioimpedance monitors) is readily facilitated, there's really no call to rely on BMI. - The problem with BMI is that it's essentially saying "if you fit our model of body fat relative to height and weight, then here is where you fall on our model of obesity". Again, for a general population this relationship holds reasonably well, but for an individual, where the question specifically is "what is my body fat percentage", BMI is the wrong tool for the job. It fails notably for specific populations of interest -- it will consistently underreport obesity in less-healthy populations, and overreports obesity in more-healthy populations. It can also result in nonsensical intervention recommendations: most unfit people will benefit by efforts to increase lean muscle mass, despite the fact that for those with lower BMIs this will decrease their putative health score by increasing overall body mass. I suspect this is among the reasons strength training is under-recommended for increasing fitness (most literature addresses "diet" and "exercise" generally, but makes little or no distinction between cardio and strength training, or focuses virtually exclusively on cardio).
dredmorbius 14y ago
A simple waist circumference measurement is more accurate than BMI at making individual assessments of obesity (> 40" ~ 100cm is bad). A set of 3-4 tape measurements (height, neck, abdomen for men; height, neck, waist, hips for women) will give a reasonable estimate of body fat. Equipment cost, about $5. http://www.linear-software.com/online.html http://www.linear-software.com/online.html Your observation of the weakness of BMI is that it tends to misreport true body fat percentage both ways. I'd hardly call that an advantage of BMI. Note that since official US government policy defines obesity in terms of BMI, technically, BMI doesn't misreport obesity. What it does is fail to correspond to true body fat percentage in any meaningful way.
- streptomycin 14y ago
  My point is that BMI is ridiculously easy for nearly everyone to measure. Your point is that a better measurement can be made if everyone goes out and buys some new thing and takes some new measurement. That seems to be in agreement with my point. > since official US government policy defines obesity in terms of BMI, technically, BMI doesn't misreport obesity The US government defining something doesn't make it true. >What it does is fail to correspond to true body fat percentage in any meaningful way. It is very meaningful. It's much better than a random guess.
  - dredmorbius 14y ago
    How are you positing people measure their weight and height without, you know, like, a scale, and, um, a tape measure? As many people in the fitness/bodybuilding field will tell you, eyeball estimates of bodyfat are in fact pretty bloody accurate. If you're interested in equipment costs, I could look up eyeballs on Amazon as I did for tape measures.
    - streptomycin 14y ago
      Most people know their weight and height already. And again, I agree that there are more accurate measurements, but they are all significantly more complicated. This time you are suggesting training people to visually estimate body fat percentage. That could work. But it's a heck of a lot more complicated than telling someone to type their height and weight into a website.
graeme 14y ago
This is true, but it's impact is overestimate. I used to hover near the 25 level for my BMI. I was muscular, so I thought it was silly. But I've not lost 6 pounds while gaining strength. I can see my abs. Turns out I was 12 pounds over my high school weight. I'd now need ~8 pounds of extra muscle to become "overweight". That's a lot. I think it's hard to go over BMI based on muscle alone. You may have less of a problem is you're BMI 25 and muscular, but you still probably could stand to lose some fat.
krschultz 14y ago
Well, I have a scale at home that does Body Fat %, and it is reasonably accurate. (It is consistent day to day, compared to a doctor's office one its off by maybe 1%). I believe it was $50. There are several on Amazon for that price and lower. If a regular scale is $20, and one that measures body fat is $40, then I don't think it's a big deal. I personally watch the body fat % now rather than weight.