On 19 Apr 2005, Christopher D. Green wrote: > "Oops, sorry," says the CDC, "obesity causes around 26,000 deaths a > year, not 365,000." > You heard it here first (from Stephen Black, I believe)
Well, it's a bit late, but I didn't want to let this pass without comment. Thank you, Chris. It's always gratifying when someone notices that you said something first (so you don't have to immodestly point it out yourself). The problem with the so-called "epidemic" of obesity is that whether it's an epidemic or not depends on where the cut-offs for BMI are placed. The lower they are, the greater the number who are deemed at risk. But like many such cut-offs, they turn out to be more arbitrary than based on firm science. The accepted cut-offs are that a body mass index (BMI) of 25 or higher is "overweight" and that of 30 and higher is "obese". "Overweight" carries the implication that health hazards start here. An illustration of an unhealthy BMI of 25 is a 5 ft 8 in person weighing 165 lb. I've been trying to see where these BMI cut-offs of 25 and 30 came from. They date from at least 1998 (see report of the US National Institutes of Health on clincial guidelines for overweight and obesity (at http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.pdf)), and are apparently based on eyeballing of the results of surveys before that date. But since that time, the literature (some of which I cited in my earlier posts) contains many challenges to the claim that doom begins at a BMI of 25. So the "new" conclusion of Flegal et al (2005) is not so surprising, if anyone had paid attention. Earlier results showed that the function relating BMI to mortality is either J or U- shaped, with a wide flat bottom, and mortality rises only slowly with BMI until quite high levels are reached. For some groups (e.g. Black women), there's no discernable increase in mortality at even the highest values of BMI. But the Flegal study (free at http://jama.ama-assn.org/cgi/reprint/293/15/1861.pdf ) does contain some startling contrasts to the conventional wisdom, more so than is conveyed in the news reports. For example, their data show relative risk of mortality at various levels of BMI, with 95% confidence intervals. The mean plus confidence interval for relative risk includes 1.0 (i.e. no increase in risk), for ages 25-69, for all values of BMI under 35, except for values under 18.5, which have elevated risk. So the real killers appear to be underweight and only severe obesity ( BMI of 35 and over; e.g. a 5 ft 8 in person weighing 230 lb). In fact, they say "The relative risk in the overweight category (BMI 25 to <30) was low, often below 1" (which means _less_ risk); thus, "Overweight was associated with a slight reduction in mortality relative to the normal weight category". Imagine that. A similar finding for obesity, BTW, was reported way back in 2001 by Katzmarzyk et al for a follow-up of the Canada Fitness Survey. They showed that the mean + 95% confidence interval for the hazard ratio (essentially a relative risk) only exceeded 1.0 for the those at BMI of 35 or above. Unfortunately, they chose to de-emphasize what they had found, inexplicably concluding "The results generally support the use of the graded classification system recommended by the WHO and the U.S. NIH fvor the identification of overweight and obesity". But what the Katzmarzyk study and the recent Flegal study instead show is that only severe obesity (35 and over) should be of concern. Another thought: the finding of increased mortality with low BMI (18.5 or less) is curious and contradictory to findings in many species (not us yet) that extreme caloric restriction can prolong life. Undoubtedly this poor showing for low BMI is helped along by the inclusion of people with low body weight due to illness. And a final thought on a prominent mortality risk factor. We all know that high cholesterol is bad, and low is good. But did you know that there's a direct relationship between cholesterol level and cognitive performance? That the lower your cholesterol, the poorer your ability to think and to perform a neurobehavioural (visuomotor) task? (I resist saying "and the dumber you are", although that's not too far off what was found). See, for example, Elias et al (2005) and Zhang et al (2004). And pass the poutine [http://en.wikipedia.org/wiki/Poutine]. Stephen References Katzmarzyk, P et al (2001). Underweight, overweight and obesity: relationships with mortality in the 13-year follow-up of the Canada Fitness Survey. Journal of Clinical Epidemiology, 54, 916-920. Flegal, K. et al (2005). Excess deaths associated with underweight, overweight, and obesity. JAMA, 293, 1861-1867 [see on-line url given above] Elias, P. et al (2005). Serum cholesterol and cognitive performance in the Framinghan heart study. Psychosomatic Medicine, 67, 24-30. Zhang, J. et al (2004). Serum cholesterol concentrations are associated with visuomotor speed in men...American Journal of Clinical Nutrition, 80, 291-8. ___________________________________________________ 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: archive@jab.org To unsubscribe send a blank email to [EMAIL PROTECTED]
