Do BMI's seem unrealistic to anyone else?

Scott_2025

I disagree completely. BMI charts are off.... My disagreement is not based on any scientific research... It is just based on observations...

I am 5' 9" male... the charts for me are as follows:
underweight < 125
normal weight 126 - 168
overweight 169 - 202
obese 203 and above

Those numbers are ridiculous....

I checked a couple BMI sites and have gotten very similar results.

I have a friend who is about my age, my height and weighs 165..... He is skinny as a rail, but he is nearly overweight by BMI standards....

If he weighed 169 he would be considered overweight.... There is no way he is within 4 ponds of being overweight....

If my friend were to weigh 125 ( 40 pounds less than he does now) he would be so skinny we would all wonder if he were near death

Scott2ndGradeTeacher

I think I read somewhere that "The Rock" (professional wrestler and "actor") has an obese BMI.

As with most things, it can be a good tool, but not a "one size fits all" method of determinating a person's body characteristics.

For me, I am "undertall"!

watfordjc

Are children as tall today as they were in 1800? Are they as tall today as they were in 1990? If an average British 15 year old today is the same height as the average British 16 year old in 1990, they will more than likely be classed as obese. That's what happens when you take a group of people of a certain age, ignore their height, and compare them to a different group of people from the past.

If you are taller or shorter than average, more or less muscular than average, have better bone density than average (the majority of the population are Vitamin D deficient), or are being compared to a group of people who are 23 years older (and currently shorter) than you, then yes BMI "normal" is unrealistic. But, since BMI is so easy to calculate, it is useful for both goals and progress tracking. Moving from one BMI range to the next one can also have a mental effect, being that statisticians would no longer consider you as obese/overweight/underweight when they take 70-300 million people and pigeonhole them into one of 4-7 groups.

llkilgore

I disagree completely. BMI charts are off.... My disagreement is not based on any scientific research... It is just based on observations...

I am 5' 9" male... the charts for me are as follows:
underweight < 125
normal weight 126 - 168
overweight 169 - 202
obese 203 and above

Those numbers are ridiculous....

I checked a couple BMI sites and have gotten very similar results.

I have a friend who is about my age, my height and weighs 165..... He is skinny as a rail, but he is nearly overweight by BMI standards....

If he weighed 169 he would be considered overweight.... There is no way he is within 4 ponds of being overweight....

If my friend were to weigh 125 ( 40 pounds less than he does now) he would be so skinny we would all wonder if he were near death

All that means is that your friend's weight falls near the upper end of the "healthy" BMI range for adults of his height. Of course he's not going to look - or be - equally healthy at every weight between 126 and 168. He's a sample of one. But the total population of 5' 9" adults includes individuals whose optimal weights fall at every point along the continuum. Standard BMI is gender neutral, you know. My sister is a tiny framed 5'9", eats whatever she wants, and effortlessly maintains her weight at ~128 pounds.

natecar

BMI uses a square function to adjust weight for a given height.
Any bonehead knows that weight correlates closely to volume, and that is a cube function of height.
Humans don't scale exactly in a cube function, but a square function is a very poor judge of humans that are outside of the 'middle' range.
Short people get diagnosed as anorexic too often with BMI
Tall people get diagnosed as overweight too often with BMI
Short fat people are not properly diagnosed
Tall overly thin people are not properly diagnosed

Unless you are the median height/build, BMI is barely worth the paper it's printed on. (coming from a 6'5" guy)

upgetupgetup

BMI uses a square function to adjust weight for a given height.
Any bonehead knows that weight correlates closely to volume, and that is a cube function of height.
Humans don't scale exactly in a cube function, but a square function is a very poor judge of humans that are outside of the 'middle' range.
Short people get diagnosed as anorexic too often with BMI
Tall people get diagnosed as overweight too often with BMI
Short fat people are not properly diagnosed
Tall overly thin people are not properly diagnosed

Unless you are the median height/build, BMI is barely worth the paper it's printed on. (coming from a 6'5" guy)

Some guy figured out a formula using a cube function:
http://www.telegraph.co.uk/health/healthnews/9816596/Interactive-calculator-do-you-win-or-lose-with-the-new-BMI.html

My result differed by 0.1 from the standard bmi chart (but i'm only a little taller than the average woman).

albertabeefy

Some guy figured out a formula using a cube function:
http://www.telegraph.co.uk/health/healthnews/9816596/Interactive-calculator-do-you-win-or-lose-with-the-new-BMI.html

My result differed by 0.1 from the standard bmi chart (but i'm only a little taller than the average woman).

Whereas mine dropped 1.7 points as a 6'3" guy. Interesting.

denezy

BMI uses a square function to adjust weight for a given height.
Any bonehead knows that weight correlates closely to volume, and that is a cube function of height.
Humans don't scale exactly in a cube function, but a square function is a very poor judge of humans that are outside of the 'middle' range.
Short people get diagnosed as anorexic too often with BMI
Tall people get diagnosed as overweight too often with BMI
Short fat people are not properly diagnosed
Tall overly thin people are not properly diagnosed

Unless you are the median height/build, BMI is barely worth the paper it's printed on. (coming from a 6'5" guy)

Some guy figured out a formula using a cube function:
http://www.telegraph.co.uk/health/healthnews/9816596/Interactive-calculator-do-you-win-or-lose-with-the-new-BMI.html

My result differed by 0.1 from the standard bmi chart (but i'm only a little taller than the average woman).

I'm 5'9" and mine dropped by 0.5.

Very interesting!

albertabeefy

and while the relationship between chronic illnesses like CV diseases & Type 2 diabetes and obesity is correlational, all signs point to yes, it's safer to assume these are related in an important way than not. And it's ridiculous to hope for a solidly causational relationship with anything related to lifestyle.

Health problems such as obesity, Type II diabetes and cardiovascular diseases are correlated to being overweight/obese in terms of body-fat percentage, yes. (We're talking body-fat here, NOT BMI).

BMI is correlated to body-fat percentage for a large segment of the population, yes. But that correlation lessens with variations in height, bone-density, skeletal structure (somatotypes), and muscle mass. As we move further either direction from average on any of those variables, the correlation of BMI to bodyfat is decreased to an exponential degree.

As such, from a statistical standpoint, people's BMI is NOT linearly-related to the health problems mentioned EXCEPT in the case of those individuals who are entirely 'average' in terms of height, bone-density, skeletal structure and muscle-mass.

neandermagnon

How likely is it that MOST people at the high end of the bmi scale have normal bf% and low waist to height ratios, or that they're athletes?

novice lifter (can't ATG squat my bodyweight yet) - I'm not "ripped" or "jacked" or whatever, not even close. I'm naturally stronger than average on account of being short and large framed (short = mechanical advantage in a lot of lifts) but only have a few months experience lifting heavy, and that was interrupted by a month's break due to surgery, so that subtracts 2 months of experience (one month off, another month getting back to my previous level of strength).

height: 5'1"
weight: 130lb
lean body mass: 101lb
body fat percentage: 22%

BMI range for my height: 100-132lb
Healthy body fat % range for women: 18-28% (can be as low as 15% if athletic and not starved)

I'm almost in the overweight BMI range at 22% body fat. At 28% body fat (high end of the healthy range) I'd be well into the overweight category. And also notice that my lean body mass is in the healthy range for my height, which means that more than half of the BMI range for my height would be unhealthily underweight for me.

I've done body fat percentage using 4 different measurements, the results range between 20% (Jackson Pollack 4-site) and 24% (Covert Bailey) - I use the accumeasure one (22%) for consistency, plus it's in the middle of the range that I get with different methods. My ribs stick out when i raise my arms above my head and I have muscle definition (and visible ribs) when flexed, but not when relaxed.

I was the same when I was 17, and the psychological effect of being told constantly (by medical professionals, at least one teacher and a sports coach, not just the chart), that I'm "almost overweight" and "need to be careful what I eat" when at that time my upper abs were visible was pretty bad. I believed that I had to lose weight and almost ended up with an eating disorder. Fortunately I went to university to do a biological sciences based degree and learned just how much of a pile of bull BMI really is. It's fine for average people, but the less average you are, the less reliable it is, and as my height is below average and my frame size above average, then it does not work for me. And if it doesn't work for me then I can assure you there are millions of others out there that it doesn't work for either, and it really is not just olympic athletes and bodybuilders that it doesn't work for.

BMI is nothing more than a measure of height against weight, it does not take into account frame size or muscle mass, both of which vary a lot, even in non-athletic populations. It varies considerably more in people who exercise regularly.

drefaw

BMI is BS, and you will never convince me otherwise .....I have 1st hand exp. with this worthless "indicator". It made my Military career a complete PITA !!

When I was in the Military, I was 235lbs, and according to my BMI of 30.2, Obese . It was a joke on my Base, as I had around 6-8% BF at all times. I actually had to go to Medical, and get waivered for my promotions ....and was forced to complete a "Fat Boys" program 1 time even ....LOL....

BMI is a JOKE .....

_Zardoz_

BMI is BS, and you will never convince me otherwise .....I have 1st hand exp. with this worthless "indicator". It made my Military career a complete PITA !!

When I was in the Military, I was 235lbs, and according to my BMI of 30.2, Obese . It was a joke on my Base, as I had around 6-8% BF at all times. I actually had to go to Medical, and get waivered for my promotions ....and was forced to complete a "Fat Boys" program 1 time even ....LOL....

BMI is a JOKE .....

So why is it the scale at fault because your Doctor or the military did not understand how to use it. It's like blaming a tape measure because you measure something wrong. BMI is a guide that's all it's meant to be and it works for the majority of the population but shouldn't be used in isolation as/ it's only an estimate. In the UK the NHS guidelines are that anyone in the over weight category needs to have two other risk factors before weight loss is recommended. BMI is a useful guide that's all it is meant to be the problem is not with the scale but huge misunderstandings of how it should be used and its limitations.

upgetupgetup

and while the relationship between chronic illnesses like CV diseases & Type 2 diabetes and obesity is correlational, all signs point to yes, it's safer to assume these are related in an important way than not. And it's ridiculous to hope for a solidly causational relationship with anything related to lifestyle.

Health problems such as obesity, Type II diabetes and cardiovascular diseases are correlated to being overweight/obese in terms of body-fat percentage, yes. (We're talking body-fat here, NOT BMI).

Are you sure? Are you sure participants in hundreds of studies dating back years were DEXA scanned? Are you sure researchers didn't mostly use BMI, or some similar metric?

BMI is correlated to body-fat percentage for a large segment of the population, yes. But that correlation lessens with variations in height, bone-density, skeletal structure (somatotypes), and muscle mass. As we move further either direction from average on any of those variables, the correlation of BMI to bodyfat is decreased to an exponential degree.

As such, from a statistical standpoint, people's BMI is NOT linearly-related to the health problems mentioned EXCEPT in the case of those individuals who are entirely 'average' in terms of height, bone-density, skeletal structure and muscle-mass.

Any single individual will not be perfectly average, by definition. But by the law of averages, it is not likely that most of the obese people in the US are athletes or big-boned.

Will repeat my argument: look at the prevalence of obesity WORLDWIDE:

http://en.wikipedia.org/wiki/File:World_map_of_Male_Obesity,_2008.svg

The US includes most genetic populations. So does Canada. The rates differ by 10%. In addition, rates in the countries people came from are by and large much, MUCH lower.

***Individual variation in frame size, skeletal structure, etc is negated by those distributions. It doesn't matter. ***

Unless you are prepared to say that Americans are MORE athletic, and have LOWER fat % than people in other nations. Which is just, I mean, I'm sorry, it's nuts.

http://en.wikipedia.org/wiki/Epidemiology_of_obesity

drefaw

BMI is BS, and you will never convince me otherwise .....I have 1st hand exp. with this worthless "indicator". It made my Military career a complete PITA !!

When I was in the Military, I was 235lbs, and according to my BMI of 30.2, Obese . It was a joke on my Base, as I had around 6-8% BF at all times. I actually had to go to Medical, and get waivered for my promotions ....and was forced to complete a "Fat Boys" program 1 time even ....LOL....

BMI is a JOKE .....

So why is it the scale at fault because your Doctor or the military did not understand how to use it. It's like blaming a tape measure because you measure something wrong. BMI is a guide that's all it's meant to be and it works for the majority of the population but shouldn't be used in isolation as/ it's only an estimate. In the UK the NHS guidelines are that anyone in the over weight category needs to have two other risk factors before weight loss is recommended. BMI is a useful guide that's all it is meant to be the problem is not with the scale but huge misunderstandings of how it should be used and its limitations.

Thanks Dr. fatdoob, but I will stick with measuring BF%, you can keep deluding yourself and everyone else that BMI is so great .....

schondell

I disagree completely. BMI charts are off.... My disagreement is not based on any scientific research... It is just based on observations...

I am 5' 9" male... the charts for me are as follows:
underweight < 125
normal weight 126 - 168
overweight 169 - 202
obese 203 and above

Those numbers are ridiculous....

I checked a couple BMI sites and have gotten very similar results.

I have a friend who is about my age, my height and weighs 165..... He is skinny as a rail, but he is nearly overweight by BMI standards....

If he weighed 169 he would be considered overweight.... There is no way he is within 4 ponds of being overweight....

If my friend were to weigh 125 ( 40 pounds less than he does now) he would be so skinny we would all wonder if he were near death

There is no way at 5'9 and 165 your friend is skinny as a rail. You're over exaggerating and at 140 he would not be rail thin either.

upgetupgetup

How likely is it that MOST people at the high end of the bmi scale have normal bf% and low waist to height ratios, or that they're athletes?

novice lifter (can't ATG squat my bodyweight yet) - I'm not "ripped" or "jacked" or whatever, not even close. I'm naturally stronger than average on account of being short and large framed (short = mechanical advantage in a lot of lifts) but only have a few months experience lifting heavy, and that was interrupted by a month's break due to surgery, so that subtracts 2 months of experience (one month off, another month getting back to my previous level of strength).

height: 5'1"
weight: 130lb
lean body mass: 101lb
body fat percentage: 22%

BMI range for my height: 100-132lb
Healthy body fat % range for women: 18-28% (can be as low as 15% if athletic and not starved)

I'm almost in the overweight BMI range at 22% body fat. At 28% body fat (high end of the healthy range) I'd be well into the overweight category. And also notice that my lean body mass is in the healthy range for my height, which means that more than half of the BMI range for my height would be unhealthily underweight for me.

I've done body fat percentage using 4 different measurements, the results range between 20% (Jackson Pollack 4-site) and 24% (Covert Bailey) - I use the accumeasure one (22%) for consistency, plus it's in the middle of the range that I get with different methods. My ribs stick out when i raise my arms above my head and I have muscle definition (and visible ribs) when flexed, but not when relaxed.

I was the same when I was 17, and the psychological effect of being told constantly (by medical professionals, at least one teacher and a sports coach, not just the chart), that I'm "almost overweight" and "need to be careful what I eat" when at that time my upper abs were visible was pretty bad. I believed that I had to lose weight and almost ended up with an eating disorder. Fortunately I went to university to do a biological sciences based degree and learned just how much of a pile of bull BMI really is. It's fine for average people, but the less average you are, the less reliable it is, and as my height is below average and my frame size above average, then it does not work for me. And if it doesn't work for me then I can assure you there are millions of others out there that it doesn't work for either, and it really is not just olympic athletes and bodybuilders that it doesn't work for.

BMI is nothing more than a measure of height against weight, it does not take into account frame size or muscle mass, both of which vary a lot, even in non-athletic populations. It varies considerably more in people who exercise regularly.

I am sorry you suffered from the carelessness of people who were responsible for you at a young age. I take your point. BMI does not account for every individual. Athletes and bodybuilders are right to be suspicious of it. And of course other factors need to be taken into consideration with other people.

I worry about people misusing (correct) criticism of poorly-applied BMI to continue to delude themselves.

upgetupgetup

BMI is correlated to body-fat percentage for a large segment of the population, yes. But that correlation lessens with variations in height, bone-density, skeletal structure (somatotypes), and muscle mass. As we move further either direction from average on any of those variables, the correlation of BMI to bodyfat is decreased to an exponential degree.

That's true. Then again, most people are sort of average height

I know you saw the amended BMI formula that I linked to earlier, which tries to accommodate height.

neandermagnon

BMI uses a square function to adjust weight for a given height.
Any bonehead knows that weight correlates closely to volume, and that is a cube function of height.
Humans don't scale exactly in a cube function, but a square function is a very poor judge of humans that are outside of the 'middle' range.
Short people get diagnosed as anorexic too often with BMI
Tall people get diagnosed as overweight too often with BMI
Short fat people are not properly diagnosed
Tall overly thin people are not properly diagnosed

Unless you are the median height/build, BMI is barely worth the paper it's printed on. (coming from a 6'5" guy)

I agree with the general gist of what you're saying, but you're assuming that height and frame size correlate (i.e. that tall people are scaled up versions of small people).... you also get short, large framed people and tall, small framed people, for whom BMI is not accurate. In fact the variation in the human population as a whole tends to be from cold adapted build (short, large frame) to tropical build (tall, slender frame) as these body types have distinct evolutionary advantages in particular climates. But there is so much variation in modern populations that you find all body types everywhere nowadays.

For people with an average frame size, it's pretty good in terms of predicting obesity based on height.... it's when frame size is non-average that there are problems. Small framed people of any height are told they're underweight when they're not, and small framed people can still fall within the normal BMI range while having more than 35% body fat (i.e. obese according to body fat percentage). Large framed people of any height can often fall in the overweight range of BMI when their body fat percentage is in the healthy range. And that's before you even get onto athletic people who have more muscle mass than average (athletic + large framed = very high likelihood of being overweight or even obese according to BMI - which is what I'd guess is the case of the person on this thread who was put in the military "fat camp" when he had a body fat percentage of 8%)

upgetupgetup

sorry and my point is that if we can mostly exclude individual variation in bone structure, frame, etc, as I think we sort of can, we are left with something else, which is other factors, like culture. and really simply said, knowing what we know about chronic illnesses in the states, even with the ****tiness of the bmi, all of that, i think it is reasonably fair to assume the space taken up by culture, on that map, (roughly) translates to adipose tissue.

but, everyone's an exception, apparently. they all live off the map.

neandermagnon

sorry and my point is that if we can mostly exclude individual variation in bone structure, frame, etc, as I think we sort of can, we are left with something else, which is other factors, like culture. and really simply said, knowing what we know about chronic illnesses in the states, even with the ****tiness of the bmi, all of that, i think it is reasonably fair to assume the space taken up by culture, on that map, (roughly) translates to adipose tissue.

but, everyone's an exception, apparently. they all live off the map.

BMI was designed for comparing populations, and as long as both populations have a similar ethnic mix, you can say, based on average BMI, that one population has more obesity than the other. This is because you can expect a similar number of large framed and small framed people in each population, so each sample group has roughly the same number of individuals within it that BMI doesn't work for, so the average is skewed by the same amount for each population, and skewed in one direction by large framed people, and in the other by small framed people, so they cancel each other out, when you're talking about averages and comparing populations. Even for comparing populations, it only works if they are the same ethnic mix, as there are ethnic differences in height and frame size that will skew the data.

With individuals, it only works if the individual has an average size frame, and it wasn't designed for diagnostic purposes in the first place. For people with non-average frame sizes, BMI is misleading and possibly dangerous - putting large framed people at risk of health problems caused by dieting to too light a weight for their frame and/or eating disorders due to being told they're fat when they're not, and small framed people at risk of heart disease due to being told they're a healthy weight for their height when they may actually be obese according to body fat percentage, plus the stress of constantly being told they're underweight when they're not (no idea if this could lead to eating disorders or not, but surely everyone wants to avoid telling healthy people that they have a health problem that they don't actually have).

It's extremely difficult to measure someone's frame size without measuring their body fat percentage and determining their lean body mass from that. (measures like wrist size are based on a general correlation, there will still be individuals that this correlation does not work for, plus if you get really fat then fat around the wrist will make the wrist bigger, and you can't reliably measure the size of bones when they're covered in fat) - given that body fat percentage directly measures how much fat someone is carrying (as opposed to guessing based on height and weight), why not just measure body fat percentage instead and use that to assess someone's health risk.... otherwise you're measuring body fat percentage to determine frame size to put BMI results into context and that's kind of a waste of time when you can just measure body fat percentage and use that to determine whether an individual needs to lose body fat or not.

Regarding people using issues with BMI as excuses or to be in denial.... well body fat percentage fixes that problem. Simply say, "okay maybe BMI doesn't work for you, it's hard to tell what size frame you have, so lets measure your body fat percentage instead". That will eliminate the people who actually have large frames or are more muscular from those who are carrying too much fat. You don't even need to measure height or frame size with body fat percentage, because it doesn't change it. And this problem would not even arise if BMI wasn't being used as the main method to determine whether an individual is obese or not, because 40% body fat is 40% body fat, not "maybe too much fat or maybe too much muscle or maybe a larger frame, we don't really know". And it will also show which slim people are lean, and which have normal weight obesity (i.e. "skinny fat"), which BMI can't do either.

So really I don't see the point in BMI at all...