BMI percentiles - where does the baseline data come from?

[Spin]

You probably all remember the pediatrician tracking your height and weight and telling you parents that you were at the X percentile for height (ie taller than X% of people your age and gender) and Y percentile for weight (ie heavier than X% of people your age and gender).

When we were growing up, being at the 50th percentile for weight probably meant that you were healthy as long as you weren't incredibly tall or short. But in ten or twenty years, with America's increasing obesity rates, will it mean the same thing? In other words, is the baseline going to stay the same, or does it update based on America's more recent generations?

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[blehm98]

it's supposed to be the healthy weight i think, not average. So the range doesn't change
doesn't really matter, i've always been way off the line anyway, athletes get no love from BMI charts

 

[MightyMoose]

You probably all remember the pediatrician tracking your height and weight and telling you parents that you were at the X percentile for height (ie taller than X% of people your age and gender) and Y percentile for weight (ie heavier than X% of people your age and gender).

When we were growing up, being at the 50th percentile for weight probably meant that you were healthy as long as you weren't incredibly tall or short. But in ten or twenty years, with America's increasing obesity rates, will it mean the same thing? In other words, is the baseline going to stay the same, or does it update based on America's more recent generations?

It's based on the most current data, so it will update. However, the healthy ranges for weight and height will likely remain the same.


I see what you're getting at though, if you were a 7 y.o. who was born in 1980, and you were in the 80th percentile for weight, today you might be in the 25th percentile for weight (assuming the same weight) due to the huge increase in obesity. I'm guessing Pediatricians will be presenting the information in a more health focused manner. Such as, in your child's height/weight (BMI) range, s/he is considered obese... etc. etc. rather than saying s/he is simply in the 80th percentile (assuming that is the case). That's my best guess.

 

[Alpha Male]

athletes get no love from BMI charts

More valid words have never been typed lol. I'm 5'9, 169lbs and have between 4-5% body fat but according to my bmi (25) i'm overweight...Oh I also have a RHR of 53bpm so go figure.

 

[Generici]

athletes get no love from BMI charts

No doubt. I'm sure that BMI is useful in population-wide studies, but it really breaks down on the individual level. Maybe one of us should develop a more appropriate tool once we're all docs!

 

[LizzyM]

I think that those tables were developed in the 1980s or earlier so you are at the 90th percentile for kids from back then...

There are some arguments that the charts aren't valid for some ethnic groups that tend to be much smaller or larger than average American white kids of yesteryear.

 

[LEUNIT]

it's supposed to be the healthy weight i think, not average. So the range doesn't change
doesn't really matter, i've always been way off the line anyway, athletes get no love from BMI charts

Truth.

More valid words have never been typed lol. I'm 5'9, 169lbs and have between 4-5% body fat but according to my bmi (25) i'm overweight...Oh I also have a RHR of 53bpm so go figure.

Dude, I'm 5'8" 168-170 lbs, 10% BF, BMI also 25 (slightly overweight). Is 4-5% BF not borderline dangerous for your health? Or are you prepping for a bodybuilding competition?

 

[WESTSIDE LOC]

4-5% is getting pretty darn low. I'm at 10% but have been lower and when I do, I always get super tired really fast...

 

[O2Doc]

No doubt. I'm sure that BMI is useful in population-wide studies, but it really breaks down on the individual level. Maybe one of us should develop a more appropriate tool once we're all docs!

Exactly. It was a tool for population studies and was explicitly stated to not be suitable for individuals. It's been widely adopted because it's so easy and medical insurance loves the crap out of it, but that doesn't mean it's accurate if your body type strays from the average (as a population tool it pretty much averages people; if 30% of the pop of NC is obese, the reason is unlikely to be that 30% of NC are bodybuilders. But if person A is obese by BMI, well...person A could very well be a bodybuilder or some other kind of athlete).

 

[Alpha Male]

Dude, I'm 5'8" 168-170 lbs, 10% BF, BMI also 25 (slightly overweight). Is 4-5% BF not borderline dangerous for your health? Or are you prepping for a bodybuilding competition?

No, I'm a wrestling coach and working out with the kids 5 days a week keeps me in excellent shape. I'm not trying to be arrogant or anything like that (too pale lol) but I eat pretty good and I have a pretty awesome metabolism (or a large tapeworm lol). Anyways, between October and March, I generally lose 6-7 lbs.

I measure it with this so maybe add a percentage point or so:
http://www.amazon.com/Omron-HBF-306C-Loss-Monitor-Black/dp/B000FYZMYK/ref=sr_1_3?ie=UTF8&qid=1300399314&sr=8-3

 

[Kevin Baker]

I believe those charts are based off of the CDC's own stats, kept here, and I believe they haven't been updated since 2000...
http://www.cdc.gov/growthcharts/

There are some other (and imo easier to calculate) more accurate health predictors than BMI, most notably the height-waist ratio. BMI is easy enough to calculate in metric countries but gets weird when you are using lbs.

Imo, using percentiles is a bad way to gauge one's health regardless as there is so much variability and one's race plays a big role in determining a healthy BMI. An average person with an Ethiopian background weighing in at the 50th percentile is likely overweight as the healthy BMI for Ethiopians is about 20.4. On the other hand, a Polynesian person weighing in at the 50th percentile is likely underweight as the healthy BMI for polynesians is 29.5*

*study
*link to website summarizing study

 

[maniacmath13]

No, I'm a wrestling coach and working out with the kids 5 days a week keeps me in excellent shape. I’m not trying to be arrogant or anything like that (too pale lol) but I eat pretty good and I have a pretty awesome metabolism (or a large tapeworm lol). Anyways, between October and March, I generally lose 6-7 lbs.

I measure it with this so maybe add a percentage point or so:
http://www.amazon.com/Omron-HBF-306C-Loss-Monitor-Black/dp/B000FYZMYK/ref=sr_1_3?ie=UTF8&qid=1300399314&sr=8-3

You're probably not 5%. The gym I work at has that hand-held one and a more accurate device that you stand on: http://www.amazon.com/dp/B000FJQ48I. The hand-held said I was 5% but the standing one said I was 10%.