Hi Stephen,
What you bring up is really interesting... What I am
still wondering about are the reasons why I am borderline overweight. I
should send a picture to make my point. I doubt there could be anyone
stating that I am even close to that. So then, does this mean I should
be skin and bones? In order to be at 23.1 BMI, I would need to lose 10
pounds. If I lost 10 pounds, my wife would tell me to start eating more
(and not because she likes chubby men...)
So, another question that pops up is as follow: If I come up as
"borderline overweight", then what is the percentage of the population
that is overweight? and is this a valid measure? Does it mean anything?
This is what you brought up in your message. If I am near overweight,
then a huge percentage of people must be, and then perhaps the
"epidemics" they are talking about is not as bad as they would have us
believe...
Food for thought (at least it won't make us bigger!)
Cheers!
JM
Stephen Black wrote:
On 20 Nov 2003, Ken Steele wrote, in response to a query from Jean-
Marc Perreault about the BMI measure of obesity::
A year or so back, I computed the BMI for myself and several members
of the ASU psychology department. All were physically active
(runners, bicyclists) and in good shape. All of us were borderline
obese according to the BMI rules at that time. So I have been wary of
that measure ever since.
We did discuss this some time (years?) ago. The conventional cut-
offs, I understand, are that 25 or over is considered overweight, and
30 or over is considered obese. A statistic I've seen is that with
these cut-offs, 80% of people over the age of 25 are overweight,
hence the term "an epidemic of obesity".
But if these criteria are to mean anything, they must be tied to some
index of health, such that those who have higher BMIs have less of
it. Life, for example. But if you look at mortality tables as a
function of BMI (e.g. Calle et al, 1999), there appears to be little
justification for setting the cut-offs as low as they are.
The curves (for non-smokers) are generally U-shaped, with a long flat
bottom, and mortality doesn't start to rise noticeably, as far as I
can see, until it gets over 32.
Another instructive paper is Fontaine et al (2003). They make some
assumptions to come up with a catchy way of making the information
meaningful, in terms of "years of life lost due to obesity" (YLL).
Their figures are interesting. For white men and women, there's no
increase until at least a BMI of 32, and then it slowly rises without
knocking off major years until around 36 or so (my eyeball estimate).
But what's really interesting are the results for black men and
women. For black men in the older age categories (60-70), BMI is
actually associated with _longer_ life (negative YLL) and doesn't
start plinking off the years until around 33-34. For black women, YLL
is negative for all age groups up until a BMI of 37! But have you
ever heard anybody tell someone that obesity was good for her?
One last point. The data does show that serious obesity (say around
35-40) is definitely a health risk. But as far as I know, there is no
study which has demonstrated that if you reduce, you live longer,
although everyone thinks it so. But it's possible that the opposite
is. For example, the metabolic crud released from the breakdown of
fat during substantial weight loss could possibly do you serious
damage. Maybe if you diet, you die.
Conflict of interest declaration: I just calculated my BMI and it's
22. So I'm not saying this for self-serving reasons.
Stephen
Calle, E. et al (1999). Body-mass index and mortality in a
prospective cohort of U.S. adults. New England Journal of Medicine,
341, 1097-
Fontaine, K. et al (2003). Years of life lost due to obesity. JAMA,
289, 187--
___________________________________________________
Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470
Department of Psychology fax: (819) 822-9661
Bishop's University e-mail: [EMAIL PROTECTED]
Lennoxville, QC J1M 1Z7
Canada
Dept web page at http://www.ubishops.ca/ccc/div/soc/psy
TIPS discussion list for psychology teachers at
http://faculty.frostburg.edu/psyc/southerly/tips/index.htm
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Jean-Marc Perreault
Yukon College
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