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[Phys-l] We are three dimensional beings. (BMI and scaling law)



MEDICINE FINALLY DISCOVERS THAT BODY MASS INDEX IS WRONG

[Suggested reason ~ next screen.]

REUTERS - Body Mass Index, the standard measure of obesity, is badly
flawed and a more accurate gauge should be developed, according to
doctors in the United States. Writing in Friday's Lancet medical
journal, the researchers from the Mayo Clinic College of Medicine,
Rochester, Minnesota, found that patients with a low BMI had a higher
risk of death from heart disease than those with normal BMI. At the
same time overweight patients had better survival rates and fewer
heart problems than those with a normal BMI.

This apparently perverse result, drawn from data from 40 studies
covering 250,000 people with heart disease, did not suggest that
obesity was not a health threat but rather that the 100-year-old BMI
test was too blunt an instrument to be trusted. . .

Maria Grazia Franzosi from the Instituto Mario Negri in Milan, writing
in the same issue of the Lancet, noted that a 52-country study
comparing four different tests -- BMI, waist-to-hip ratio, waist
measure and hip measure -- found that waist-to-hip was the best
predictor of heart attack risk. "BMI can definitely be left aside as a
clinical and epidemiological measure of cardiovascular risk," she said.
"Uncertainty about the best index of obesity should not translate into
uncertainty about the need for prevention policy against excess
bodyweight," she cautioned.

http://go.reuters.com/newsArticle.jhtml?type=healthNews&storyID=13231437&src=rss/healthNews




BUT STILL DOESN'T UNDERSTAND WHY. . .

AS WE HAVE POINTED OUT, BMI doesn't work for a simple reason: humans
are not two dimensional creatures. Any formula for assessing proper
weight must be based on a cubing of proportions rather than squaring
them. This stunning error by the medical profession - and an
unskeptical media - has done all sorts of harm to patients who have
been badly diagnosed.

And there are other problems with this simplistic measure other than
bad math - such as its failure to distinguish between fat and muscle.
Looking for a good explanation of this, we oddly found two of the best
descriptions on an electronic game site and the site of an MBA.

BRYON HALL, FATAL GAMES - BMI has been criticized widely because it
does not take into account body build. Therefore, a fitness trainer
may mistakenly tell their client that the client is slightly
overweight according to their BMI, when in fact they are fit but
merely have an athletic build. I knew this before I began using it
with F.A.T.A.L.

However, when I began extrapolating height and weight proportions to
larger and smaller humanoids such as elves or giants, who were still
generally meant to have a build at least similar to an average human,
I got strange results. Unless I were also using the Cube-Square Law, I
probably would not have noticed how BMI went askew. . . The
Cube-Square Law relates to the proportions of larger and smaller
creatures. For example, as a creature increases proportionately in
size, its surface area increases by a ratio of the difference in
height squared, but the weight increases by the ratio of the
difference cubed. . As a measure, BMI results vary with height.

MBA TOOLBOX - The Body Mass Index Is wrong because the "weight" is
expressed as a function of the square of the height. That might be ok
if we had two dimensional bodies, height and depth or height and
width. In fact, we have three dimensional bodies: height, width and
depth. Therefore "weight" must be expressed as a function of the cube
of the height. This problem is the biggie. Fortunately, it can easily
be dealt with by changing the mathematical formula.

A BETTER BMI CHART
http://www.flickr.com/photo_zoom.gne?id=95090078&size=o

http://www.mbatoolbox.org/stories/storyReader$33


bc, who, if he remembers correctly, knows this is a favo of JD's.