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 _______________________________________________ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
