Re: Body Mass Calculator


David Wright wrote:
In article <1146591318.850308.208680@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
PeterB <pkm@xxxxxxxxxxxxxxx> wrote:

vernon wrote:
"PeterB" <pkm@xxxxxxxxxxxxxxx> wrote in message
news:1146583245.523600.103600@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

David Wright wrote:
In article <1146497093.261275.197450@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
PeterB <pkm@xxxxxxxxxxxxxxx> wrote:
http://nhlbisupport.com/bmi/

Please note that "body mass index" is not terribly useful for anyone
aside from sedentary populations. Just because it says you're
'overweight' doesn't mean you are, and just because it says you're NOT
overweight isn't an automatic reason to relax.

Nonsense. If you fall within the recommended ranges, you know you're
better off (statistically) than those who don't.

The heavier you are, the more it hurts when you fall and the harder it is to
get up.

My stupidity being said, body mass calculator is often not usefull only
because of innacuracy.
For instance, I have large bones and have a better than normal muscle mass.
When I use the "calculator", I am "fat"
When I use the water displacement, impedance measurement or professional
pinch test, I am very lean.

BMI is based on what's true for most people, but will overestimate body
fat in a few (probably less than 2%.) It will even underestimate body
fat in a few, mainly the elderly.

Whenever I see the word "probably" in a PeterB posting, I now know it
translates into "this is something I wish were true, I have no
evidence that it's true, and it usually isn't true."

You're wrong. And you shouldn't dissuade people from using a
meaningful metric that can save their lives. The BMI is especially
useful in populations where obesity rates are high.

Such is the case, here. I've just spent some time rummaging around in
PubMed, and I find that BMI correlates quite poorly with body fat
percentages in many populations.

BMI isn't designed to measure the percentage of body fat, so your point
is meaningless.

It works OK in girls and quite
poorly in adolescent boys, and it's all over the map much of the rest
of the time.

That's why the BMI-for-age is used for children. Here is an online
tutorial you need to take from CDC to understand how BMI is used, for
whom, and with what diagnostic followups:

http://www.cdc.gov/nccdphp/dnpa/growthcharts/training/modules/module1/text/intro.htm

Since I know you won't bother, here is a excerpt for you:

"Like weight-for-stature, BMI is a screening tool used to identify
individuals who are underweight or overweight. BMI is NOT a diagnostic
tool (Barlow and Dietz, 1998). For example, a child who is relatively
heavy may have a high BMI for his or her age or high
weight-for-stature. To determine whether the child has excess fat,
further assessment would be needed and that might include skinfold
measurements. To determine a counseling strategy, assessments of diet,
health, and physical activity are needed. For children, BMI is gender
specific and age specific (Hammer et al., 1991; Pietrobelli et al.,
1998). Because BMI changes substantially as children get older,
BMI-for-age is the measure used for children ages 2 to 20 years." And,
"BMI is used as a screening tool to identify possible weight problems
for children. CDC and the American Academy of Pediatrics (AAP)
recommend the use of BMI to screen for overweight in children beginning
at 2 years old."

Also:
http://www.cdc.gov/nccdphp/dnpa/bmi/childrens_BMI/about_childrens_BMI.htm

BMI also tends to underestimate obesity (where obesity refers to
percentage of bodyfat).

BMI cannot "tend" to underestimate or overestimate because it isn't a
diagnostic tool in the first place. It's a range of values that
suggest a problem at the margins. BMI allows you assess a relative
disease risk using a range of values based on large pool of data. If
you want to measure the exact amount of body fat (or head fat) you
happen to be carrying, you'll need an actual diagnostic.

-- David Wright :: alphabeta at prodigy.net
These are my opinions only, but they're almost always correct.
"If you can't say something nice, then sit next to me."
-- Alice Roosevelt Longworth

.

Relevant Pages

  • Re: Body Mass Calculator
    ... PeterB wrote: ... body mass calculator is often not usefull only ... BMI is based on what's true for most people, ... fat in a few, mainly the elderly. ...
    (misc.health.alternative)
  • Re: Body Mass Calculator
    ... body mass calculator is often not usefull only ... fat in a few, mainly the elderly. ... A friend whose BMI ... Same with exercise. ...
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  • Re: Body Mass Calculator
    ... vernon wrote: ... body mass calculator is often not ... BMI is based on what's true for most people, ... fat in a few, mainly the elderly. ...
    (misc.health.alternative)
  • Re: Body Mass Calculator
    ... PeterB wrote: ... body mass calculator is often not usefull only ... BMI is based on what's true for most people, ... fat in a few, mainly the elderly. ...
    (misc.health.alternative)
  • Re: Body Mass Calculator
    ... vernon wrote: ... body mass calculator is often not usefull ... fat in a few, mainly the elderly. ... A friend whose BMI ...
    (misc.health.alternative)