Forget BMI

24

Replies

  • cwolfman13
    cwolfman13 Posts: 41,865 Member
    Just look in the mirror and take an honest look at yourself.

    Yup...KISS
  • Ironandwine69
    Ironandwine69 Posts: 2,432 Member
    ferd_ttp5 wrote: »
    BMI tells me I'm fat.
    **kitten* this :lol:
    Not sure how you kitten something, but okay lol.
  • Ruatine
    Ruatine Posts: 3,424 Member
    edited May 2017
    Oh, jeez, I just realized that I was calculating my *maximum* weight according to BMI. That 182.5lbs is a BMI of 25 for me. If I go for the low end, a BMI of 19? My weight should be 138.7lbs. That's laughably implausible for me.

    Yeah... it's a range for a reason. Not everyone should be at the bottom of the range just as not everyone should be at the top of the range.

    Normal BMI range =/= healthy

    It's very easy to be overfat in the normal BMI range, which is opposite of what many people want to believe (i.e. that it's easy/common to have a good body fat % in the overweight/obese ranges).

    BMI is a single tool in a plethora of measurements to determine if someone is at a healthy weight.
  • stanmann571
    stanmann571 Posts: 5,727 Member
    Bottom line is BVI will reduce the percentage of outliers
  • macchiatto
    macchiatto Posts: 2,890 Member
    macchiatto wrote: »
    That is interesting; thanks for posting. My husband is one for whom BMI is off. He's been losing weight and does still have a bit more to lose but nothing like BMI would indicate. I also just looked at the measurements we last took for him (he's lost a bit more since then) and waist was 39.75" even though he's now right on the border between "obese" and "overweight" per BMI.

    I don't have time to research this more right now, but anyone know for this if waist measurement they're going by is the narrowest point between rib cage and hips, or belly button level? My belly button definitely migrated lower thanks to pregnancy so now that measurement is pretty close to my hip measurement. :/ BMI is 20.1 now, true waist is 28.5" but belly button level "waist" measurement is right around 35".

    For women it's the narrowest point.

    Perfect; thanks!
  • pedermj2002
    pedermj2002 Posts: 180 Member
    edited May 2017
    Ruatine wrote: »
    BMI is a single tool in a plethora of measurments to determine if someone is at a healthy weight.

    And that nicely ignores the entire point of the previous post I made: BMI may actually work for some people. You might be one of the lucky ones it *does* work for. But a tool to help diagnose health with a failure rate of 18% is not a useful tool. That's nearly one in five.

    Think of it this way: I set out 5 cups in front of 5 people. Four of them have sugar, one of them has salt. You get to pick one, and whatever you pick you have to consume all of it. Only four of you have to pick a cup though. Would that last person take the last cup, or simply pass?

    Change it to cups of water, one of which is poisoned. Make it just you. Would you take your chances on it then?

    I doubt I'd be willing to take a cup in either of those challenges. Most other people wouldn't either. And yet, using that tool, people are labeled, categorized, and viewed as either healthy or unhealthy. It's really bad, and needs to stop being used.

    Oh, and here's another tidbit that came from that article: "31 percent who were of normal weight according to B.M.I. had excess body fat." That means that, for 49% of the people out there, BMI gives them broken information about their current fat levels.

    This means that for a mere 51% of the population, BMI is useful.

    When you know that, BMI is not a reasonable guide anymore.

    *edit* I screwed up math.31+18 is 49, not 59. Woops.
  • Ruatine
    Ruatine Posts: 3,424 Member
    edited May 2017
    Ruatine wrote: »
    BMI is a single tool in a plethora of measurements to determine if someone is at a healthy weight.

    And that nicely ignores the entire point of the previous post I made: BMI may actually work for some people. You might be one of the lucky ones it *does* work for. But a tool to help diagnose health with a failure rate of 18% is not a useful tool. That's nearly one in five.

    Think of it this way: I set out 5 cups in front of 5 people. Four of them have sugar, one of them has salt. You get to pick one, and whatever you pick you have to consume all of it. Only four of you have to pick a cup though. Would that last person take the last cup, or simply pass?

    Change it to cups of water, one of which is poisoned. Make it just you. Would you take your chances on it then?

    I doubt I'd be willing to take a cup in either of those challenges. Most other people wouldn't either. And yet, using that tool, people are labeled, categorized, and viewed as either healthy or unhealthy. It's really bad, and needs to stop being used.

    Oh, and here's another tidbit that came from that article: "31 percent who were of normal weight according to B.M.I. had excess body fat." That means that, for 59% of the people out there, BMI gives them broken information about their current fat levels.

    This means that for a mere 41% of the population, BMI is useful.

    When you know that, BMI is now an unreasonable guide for more people than those for whom it isn't.

    I didn't ignore your point at all. You made a point about the low end of the normal BMI range being implausible for you, and I agreed. For many, being at the low end of the normal BMI range is not appropriate. Neither is being at the high end of the BMI appropriate for many. BMI is a range to account for factors like sex and body type. It's a single measure of many for determining a healthy weight range, but too many people, especially on MFP where we have an overly biased population, want to believe that they are BMI outliers.

    Being a BMI outlier is mostly to do with muscle mass. High muscle mass = overweight/obese BMI but low bodyfat %. Low muscle mass = normal BMI but high bodyfat %. For people who need to lose weight, BMI is useful tool for determining how much weight they should lose to lower their weight-related health risks. Like @AnnPT77 I've seen one too many people who really do need to lose fat, disregard BMI because they've heard people disparage it as a measure of healthy weight.
  • pedermj2002
    pedermj2002 Posts: 180 Member
    I think you didn't read the link I provided, so I'll spell it out here: https://www.nytimes.com/interactive/projects/cp/summer-of-science-2015/latest/how-often-is-bmi-misleading

    BMI is a misleading statistic, and badly so. Under the absolute best possible interpretation of that article (being most favorable to BMI), nearly one out of every 5 people will be misled about their current fat levels and how healthy those fat levels are for them. Under the worst possible interpretation of that article, it becomes one out of every two.

    To put it in human terms: If you work with a team of four other people, then one of the people on your team (including you) is being misled by BMI (under the best possible conditions). Under the worst, at least two people on that team are.

    And the BMI data can be wrong in *both* directions: It can tell you you're okay, even though you're in dangerously high body fat percentage territory. It can tell you you're not okay, even though your body fat is extremely low and muscle mass is extremely high.

    Your interpretation of what an "outlier" is, with respect to BMI, is flawed. When you state that being an outlier is mostly to do with muscle mass, you're thinking of people who have lots of muscle mass for whatever reason. The other direction happens too, where they have too much body fat and not enough muscle mass, and those people are actually in danger but will be told they're okay because their BMI labels them as "normal".

    That's why I advocate for getting BF % measured using *anything* other than BMI. Find out the reality about your body and work with that. You can even go with pictures online for a free way to compare (see https://www.tasteaholics.com/wp-content/uploads/2015/10/Body-Fat-Percentage.jpg for one example). Literally *any* option is better than BMI, but people get hung up on it because it's all they know.
  • Ruatine
    Ruatine Posts: 3,424 Member
    I think you didn't read the link I provided, so I'll spell it out here: https://www.nytimes.com/interactive/projects/cp/summer-of-science-2015/latest/how-often-is-bmi-misleading

    BMI is a misleading statistic, and badly so. Under the absolute best possible interpretation of that article (being most favorable to BMI), nearly one out of every 5 people will be misled about their current fat levels and how healthy those fat levels are for them. Under the worst possible interpretation of that article, it becomes one out of every two.

    To put it in human terms: If you work with a team of four other people, then one of the people on your team (including you) is being misled by BMI (under the best possible conditions). Under the worst, at least two people on that team are.

    And the BMI data can be wrong in *both* directions: It can tell you you're okay, even though you're in dangerously high body fat percentage territory. It can tell you you're not okay, even though your body fat is extremely low and muscle mass is extremely high.

    Your interpretation of what an "outlier" is, with respect to BMI, is flawed. When you state that being an outlier is mostly to do with muscle mass, you're thinking of people who have lots of muscle mass for whatever reason. The other direction happens too, where they have too much body fat and not enough muscle mass, and those people are actually in danger but will be told they're okay because their BMI labels them as "normal".

    That's why I advocate for getting BF % measured using *anything* other than BMI. Find out the reality about your body and work with that. You can even go with pictures online for a free way to compare (see https://www.tasteaholics.com/wp-content/uploads/2015/10/Body-Fat-Percentage.jpg for one example). Literally *any* option is better than BMI, but people get hung up on it because it's all they know.

    Except that I specifically stated that it goes both ways.
    Being a BMI outlier is mostly to do with muscle mass. High muscle mass = overweight/obese BMI but low bodyfat %. Low muscle mass = normal BMI but high bodyfat %.

    Also, yes, I did look at your article, but I honestly found some of the data they were linking suspect, as it wasn't what the studies were saying (typical of media).

    Both of these studies, on the other hand, are quite interesting and aren't filtered through a journalist's non-scientific, headline grabbing bias:

    http://ajcn.nutrition.org/content/89/2/500.full (Comparisons of percentage body fat, body mass index, waist circumference, and waist-stature ratio in adults)
    http://ajcn.nutrition.org/content/72/3/694.full (Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index)

    BMI is not perfect. BMI is not an indicator of a specific body fat % (I say this, because you said, "That's why I advocate for getting BF % measured using *anything* other than BMI."), although in one of the studies I linked, the researchers gave it a damn good go.
  • pedermj2002
    pedermj2002 Posts: 180 Member
    SezxyStef wrote: »
    BMI is not a measure of BF% anyway it is a measure of weight...and for that it is valid for the majority of people.

    This is completely incorrect. BMI is a measure of weight compared with height. The formula is actually pretty simple: weight (in kg) divided by the square of the height (in meters). That's it. BMI is not a measure of weight, it's a measure of a proportion of weight to height.

    Do other methods have issues? Sure, all the time. None of them are as badly misleading as BMI though, not with how BMI is used.

    Look, for me, today, my numbers are 1.84m and 98.07kg. So, plugging them in: 98.07/(1.84*1.84) = 28.97 BMI. Maximum "normal" BMI is 25, so I've got a ways to go before I reach "normal" BMI. Going by this picture, I'm somewhere in the 20%-24% range. Going by the New York Times article, I'm in a "healthy" range of BF% (I want to be lower than that, so I'm working on it, but that's where I am now).

    But anything is better than BMI. A tool with an error rate that high is a tool that needs to be relegated to the dustbin of history. Calipers can be miscalibrated. DXA scans can be impacted. BodPods have their own errors. Tape measures might not be measuring the exact same locations on the body from day to day. Even plain old scales can be wrong depending on their exact location on the earth, if they haven't been calibrated for that location or are sitting on material that affects their ability function (carpet vs tile, for instance). But what all of them have in common is accuracy, even on a bad day, that beats out BMI.

    Yes, the CDC pushes BMI. Yes, it can be used as a tool for a significant chunk of the population. But an error rate that high (and especially on false positives where the person is told they're okay!) is absolutely horrific.

    That's why I used the sugar/salt and poison/not poison analogies. Errors are places where a tool breaks down. By definition, you can't predict them (if you could, you'd prevent them), making them effectively random. So, would you be willing to trust a random "grab this cup and drink it" if you knew that 31% of the time it would give you a problem? I know that I wouldn't, and I'd be shocked if others would, *especially* if the benefit from it is so minimal.

    That's why I say to abandon it. It's not complex math. And it provides false information all too often.
  • SezxyStef
    SezxyStef Posts: 15,267 Member
    SezxyStef wrote: »
    BMI is not a measure of BF% anyway it is a measure of weight...and for that it is valid for the majority of people.

    This is completely incorrect. BMI is a measure of weight compared with height. The formula is actually pretty simple: weight (in kg) divided by the square of the height (in meters). That's it. BMI is not a measure of weight, it's a measure of a proportion of weight to height.

    Do other methods have issues? Sure, all the time. None of them are as badly misleading as BMI though, not with how BMI is used.

    Look, for me, today, my numbers are 1.84m and 98.07kg. So, plugging them in: 98.07/(1.84*1.84) = 28.97 BMI. Maximum "normal" BMI is 25, so I've got a ways to go before I reach "normal" BMI. Going by this picture, I'm somewhere in the 20%-24% range. Going by the New York Times article, I'm in a "healthy" range of BF% (I want to be lower than that, so I'm working on it, but that's where I am now).

    But anything is better than BMI. A tool with an error rate that high is a tool that needs to be relegated to the dustbin of history. Calipers can be miscalibrated. DXA scans can be impacted. BodPods have their own errors. Tape measures might not be measuring the exact same locations on the body from day to day. Even plain old scales can be wrong depending on their exact location on the earth, if they haven't been calibrated for that location or are sitting on material that affects their ability function (carpet vs tile, for instance). But what all of them have in common is accuracy, even on a bad day, that beats out BMI.

    Yes, the CDC pushes BMI. Yes, it can be used as a tool for a significant chunk of the population. But an error rate that high (and especially on false positives where the person is told they're okay!) is absolutely horrific.

    That's why I used the sugar/salt and poison/not poison analogies. Errors are places where a tool breaks down. By definition, you can't predict them (if you could, you'd prevent them), making them effectively random. So, would you be willing to trust a random "grab this cup and drink it" if you knew that 31% of the time it would give you a problem? I know that I wouldn't, and I'd be shocked if others would, *especially* if the benefit from it is so minimal.

    That's why I say to abandon it. It's not complex math. And it provides false information all too often.

    it is not completely incorrect actually....and I actually know the history and how it is calculated and what it is used for so I don't need a lesson thx.

    But you are fighting a losing battle...BMI is a good for what it is used for...just like other tests that aren't 100%...

    And if you for one minute think a scale or a set of calipers or a BIA scale is 1oo% better than BMI and you ahve said it more than once I am out as you can lead to water but you can't force to drink and being ignorant is your choice.
  • pedermj2002
    pedermj2002 Posts: 180 Member
    I had begun weight loss by then, and was down by 40lbs. Maybe the biking I started a few months before made enough of a difference? I don't know. I just know what I had on the printout they gave to me.
  • bbell1985
    bbell1985 Posts: 4,571 Member
    I'm pushing right outside of a normal BMI right now. I know I'm not super slim but I'm pretty fit. I'm not concerned about what it says because I'm athletic, but I am a few pounds above the physique I prefer.
  • Packerjohn
    Packerjohn Posts: 4,855 Member
    I had begun weight loss by then, and was down by 40lbs. Maybe the biking I started a few months before made enough of a difference? I don't know. I just know what I had on the printout they gave to me.

    Understand you are going off the test result. A few months of casual biking does not build much muscle. As you lose weight, I would not be surprised if you found the 180 range just fine.
  • gmallan
    gmallan Posts: 2,099 Member
    BMI tells me I'm fat.

    Well that's actually the main problem with BMI. It doesn't tell you anything about how much fat you have just scale weight compared to height.
  • SezxyStef
    SezxyStef Posts: 15,267 Member
    Something occurs to me in this discussion which is a point that hasn't been raised, and please correct me if I'm wrong, but when you're given a figure in those scans for fat free mass, that includes everything including water in your tissues, and that weight also decreases when you lose fat as you lose additional weight. As you lose weight you will also lose additional muscle tissue.

    In other words, I'm kind of perplexed from how I understand weight loss works how this discussion is continuing on the premise that a reading on fat free mass is being considered to be a constant that will stay no matter what happens with weight loss.

    I didn't think that was how it worked.

    I read back and I see where I'm misunderstanding this somewhat, but I'm not sure this shouldn't have been said because of it sounding like an impossibility that fat free mass would "be removed".

    I think the bod pod was wrong, frankly.

    exactly ...my son is 6 ft 4...190lbs...recently gained 10....and at 180 he was still not too lean...and he wears a size 11 shoe...aka not a small lad @22 years old...

    my husband is 184lbs....at 5 ft 11...not lean but not fat either...a good weight...solid...but has a bit of a belly...

  • moonstroller
    moonstroller Posts: 210 Member
    SezxyStef wrote: »
    BMI tells me I'm fat.

    no BMI does not tell you that...

    it tells you one of a couple thing

    underweight
    normal weight
    overweight
    obese
    morbidly obese

    if it tells you that you are overweight and you don't think so one of two things is going on.

    You are an outlier or you need to reevaluate what you are seeing.

    BMI doesn't take in to account body fat vs muscle mass, so the number is utterly meaningless without understanding body composition.


    You are exactly on target. When I was in excellent shape years ago I was doing a lot of lifting so I weighted 178 pounds with under 7% body fat and wore size 30 pants. BMI had me as being overweight, but it's overall body composition that matters.
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