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BMI inaccurate for very short and very tall people?


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I've read in a couple of places that BMI is less accurate for people who are very short or very tall.   Here is an example: http://www.blurtit.com/q300727.html

According to this respondent "the ratio (weight divided by square of height) doesn't perfectly represent the best proportion between height and weight (something you can usually see with your eyes). So effectively, the BMI formula 'allows' short people (under 5'2') to be relatively heavier than tall people (above 6')."

The American Institute for Cancer research states "BMI may not be an accurate measure for everyone, including people who have more muscle mass, like athletes; seniors with less muscle mass; or for people under 5 feet tall."
http://www.aicr.org/site/PageServer?pagename= dc_oo_measure

And this article says "Very short people (under 5 feet) may also have high BMI numbers that do not reflect their degree of fatness."
http://health.msn.com/weight-loss/articlepage .aspx?cp-documentid=100173489



Do you think that's true?  Is there a better way to generally determine the ideal weight for very short and tall people, beside complex measures such as body fat testing?
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Personally, I think we need to stop sticking people in boxes, by saying you should only weight XYZ.  There are so many elements to be considered when looking at physical health.  I personally am nearly 6' tall and I have weighed within the BMI range once in my life.  I looked like a corpse.  I have no doubt that the BMI figures are not the be all and end all.

I think that people should judge their weight upon what looks good on them.  A firm, but not skeletal figure, healthy skin and hair and the ability to perform daily tasks without keeling over seems like a good start.

Technically my BMI puts me in the overweight category...5'5", 154 pounds.  My mom at the same height weighs 135 and is in the healthy BMI range.  I wear the smaller clothes so even though my BMI may be higher I prefer my figure.

BMI is a wide range deliberately.  Between 19 and 25 there's usually about 28lbs difference. There is no one 'ideal' BMI because there are a lot of different frames and builds.   The apocryphal story of the professional heavy-set rugby player being technically obese on the BMI scale is often bandied around.  But I don't think that proves the BMI test is 'rubbish'... just that it doesn't apply to a very small minority.   The BMI scale should never be dismissed in order to rationalise being underweight or overweight.   

What are good supplements to the BMI for people who are in the minority? The Boy Scouts of America uses BMI to disallow "obese" people from their high adventure camps which results in a number of football players not being able to attend even though they are in good physical condition.

Obviously BMI in general is not accurate 100% of the time, I was just wondering if others thought it might be skewed in particular when it came to people of extreme heights.

It also doesn't work very well for muscular people, especially muscular men. Although my fiance could do with losing a few lbs he is not obese by any means, just extremely muscular and also "big boned". However, he comes up as obese if we go by BMI. In cases such as this it is better to go by inches.

I am 6 foot tall and I drop from overweight into the healthy weight category at 183 lbs.  At 183, I still have a good bit of jiggle on my thighs and a good bit (more than I like) around my waist and hips.  I think I look and feel the best at 165-170 lbs which irronically falls directly in the middle of the healthy weight range on the BMI.

My husband is very broad in shoulders and chest, 6 ft 2 in, and often falls in the overweight category while at the same time measuring at around 11% body fat.  I would consider him in the athlete category.  He swims, lifts, runs, and cycles regularly.  In my family picture in my profile, my husband is at a BMI of 27 and also at the lowest weight he has been at since junior high.

My point is that my husband and I are both considered tall.  For me, an average person that spends about 3-4 hours a week exercising, the BMI scale seems to be a good measurement of a healthy weight.  For my husband, a more serious athlete with a good deal of muscle mass, the BMI seems to be a bit skewed. I think height is not the factor that throws it off.

All of these thing work on a bell curve.  If you don't know what this is, you can see the pics here.  The center part of the bell curve is where 80-90% of people fall and it's fairly valid for them.  The people that it doesn't work so well for are the people who fall on the outside edge - either way - of the bell curve.  Overly fit or overly obese.  Overly tall or overly short.  It doesn't much matter.  The further you're out from the center, the less it applies to you. 

It actually makes reasonable sense to me that for very tall and very short would be inaccurate. I've often wondered why it's weight divided by the square of height, I would think that weight should be more proportional to the cube of height (since mass is based on volume, and if height increases by x%, one would expect every diminsion to increase x%). In any case, even if the BMI was determined empirically, I wouldn't be surprised if the exponent of height was rounded to two for simplicity purposes, but that would mean that people at the etremes of height would deviate significantly in their BMI.

The disadvantage about BMI is that it doesn't take into account body composition at all. For measuring obesity in populations, it's decent, because everything averages out (some people will be classified as overweight when they're healthy, and vice versa). But I think there's enough variation in individuals that BMI should not be a "be all end all" device for most people, at most a very general guidline
Oooo, awww, normal distribution *drools*
#11  
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Hey another tall girl here...

I had an interesting experience taking my kids to the pediatrician. My daughter is 4 and my son is 2...both are extremely tall for their age and by no means fat. However, my daughter's bmi is creeping up past the 18 point...which could be troublesome...especially if you follow the bell curve into adult hood. However my pediatrician reassured me and told me that bmi is inaccurate for the very tall and that he prefers to go on what kids look like and what they can do. It was the first time in my life I had heard this perspective from an actual doctor and it made me feel hopeful that my son and daughter would not be subjected to a medical world that can only see numbers and can't seem to see actual physical health.

 

Original Post by smartjock256:

I would think that weight should be more proportional to the cube of height (since mass is based on volume, and if height increases by x%, one would expect every diminsion to increase x%). In any case, even if the BMI was determined empirically, I wouldn't be surprised if the exponent of height was rounded to two for simplicity purposes, but that would mean that people at the etremes of height would deviate significantly in their BMI.

i consider myself a fairly intelligent individual, but that just went WAY over my head, lol!!!

I think the BMI scale thingy is just inaccurate in general. Once, my dad was playing Wii Fit and he is really big and bulky muscular. Like spider veins. He is 5 ft 11 in, and he is like...kinda over 300 and it said he was obese.

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