Re: Body Mass Calculator


David Wright wrote:
In article <1146670786.888834.141210@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
PeterB <pkm@xxxxxxxxxxxxxxx> wrote:

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.

PeterB, do you even bother to *read* the swill you write? Let's take
a look at two of your statements from this thread, conveniently
juxtaposed:

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.

and

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

So first you tell us that it overestimates or underestimates in a tiny
percentage of cases, then you tell us that it isn't designed to
estimate body fat.

The first point was made to address the idea that BMI might be a way to
measure obesity, which it isn't actually intended to do. My comment
was simply to show that even with that being the case, it still
effectively identifies obesity in most people, especially in a
demographic like the US. The second comment was simply a reminder that
BMI is not a diagnostic tool. As usual, you're inability to parse (or
your pretense at such) makes you look dumb. But why would you want to
look dumb? Oh, that's right, you don't *want* to look dumb, that's
just how it works out when pharma blogging is put under the light.

My point, which apparently escaped you entirely, is that you were
wrong in your original statement that BMI provided an accurate
estimate of body fat.

I wasn't wrong. BMI accurately identifies obesity in most people, but
not everyone (especially athletes, who tend to be aware of their body
fat profile already.) It also has greater utility on the high end,
exactly where it's needed most. See the study at
http://www.nature.com/ijo/journal/v29/n1/full/0802735a.html and the
synopsis at http://www.surgicalteam.com/obesity/bmi_calculator.htm and
also at
http://www.sign.ac.uk/guidelines/fulltext/69/section2.html

BMI would, I'm sure, not provide a correct
estimate of the amount of fat in your head, which must approach 100%
in your case.

But if it measures a range of values into which your head fat falls,
and assesses your relative disease risk as a result, and does so with
85% or better accuracy, it does exactly what the BMI is designed to do.


BMI has moderate value as a screening tool in sedentary populations,
and that's about it.

Bull***. BMI is highly effective in identifying obsesity, period.
Where is the line between sedentary and non-sedentary? If I mow my
grass and walk half a mile to work, but have a BMI of 28, I still might
have a weight problem. You're just being dumb.

-- 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

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