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Wednesday, August 23rd 2006

As I Stuff Greasy Pizza & Cola Down My Throat…

Lots of “new” information on the effects of obesity on early mortality. The August 24th issue of the NEJM dedicated a lot of space to overweight issues. A large study of AARP members found that even a slight increase in excess body weight can increase the chance of early mortality.

From the Boston Globe (picked up in the Seattle PI),

Those who were obese doubled or tripled their chances of dying prematurely, the study found.

“This may not be the news a lot of people want to hear, but I think the study provides pretty clear evidence that being overweight is not a benign condition and we shouldn’t be complacent about it,” said Dr. Frank Hu of the Harvard School of Public Health, who was not involved with the study.

Well, from across the aisle comes conflicting news! The Lancet published a study that reviewed forty studies which linked increased Body Mass Index to increased mortality (which is exactly what the linked to NEJM study did). And what did they find?

overweight (BMI 25–29.9) had the lowest risk for total mortality…and cardiovascular mortality …compared with those for people with a normal BMI. Obese patients (BMI 30–35) had no increased risk for total mortality or cardiovascular mortality. Patients with severe obesity (≥35) did not have increased total mortality…

Yes, you read that right, overweight individuals (as defined by BMI) had a lower total mortality than normal weigh individuals. And obese individuals showed no increase in total mortality.

Can’t these scientists agree on anything?!

Pure Pedantry, over at ScienceBlogs (where Orac & Dr. Charles have both set up) goes over the study and why BMI may be a poor indicator of risk.

The Waifish and Unhealthy — The third one is interesting. There they are basically saying that we assume thin people in this society are healthy when that is really not necessarily the case. For example, you could have a very thin person who smokes like a chimney. They are really raising their cardiovascular risk, but if you look at them — and more importantly measure their BMI — you would miss that. Because overweight people are more likely to have other risk factors, they have doctors riding them all the time to stop. Thin people get off easy.

People Who Carry Their Weight Low — Finally, we know that fat distribution matters. You remember all that stuff about apple shaped people and pear shaped people. Well, we know that where fat is on your body matters in determining your risk. If you for instance carry your fat in your butt, then the risk associated with being overweight is significantly less than if you carry it in your chest.

All of these are reasonable explanations for why BMI is a relatively blunt instrument for determining CAD risk. The paper they mention at the end — the INTERHEART study — suggests that waist circumference or waist-to-hip ratio might be more effective ones.

This doesn’t really jive with the fact that the NEJM study looks at smoker status, alcohol intake, and broadly ongoing chronic disease for their study; and even with those considerations still doesn’t like the overweight’s odds versus people with a normal BMI.

I doubt your PCP is going to be telling you that having an increased BMI isn’t a health risk any time soon.