James Joyner, no doubt with middle age glaring over his shoulder, muses over a post on why Americans keep getting fatter but keep living longer:
Many of the recent advances in medicine have specifically aimed at ameliorating the effects of obesity and high cholestorol. We’ve also gotten radically better at neo-n
Beyond that, it’s also quite possible that advances in medicine are a small part of the story.
- Violent crime is down.
- So are deaths in auto accidents.
- We’re less likely to get killed on the job – directly offsetting the fact that sitting behind a computer all day makes us more likely to get fat.
- We’re not losing tens of thousands of people to war every few years.
I’m sure I’m missing half a dozen other contributing factors. What are they?
One possible additional reason is that being fat isn’t as big a risk as the popular mind imagines.
Another possibility is that we’re getting very bad advice on diet and better advice on a lot of other things.
A third possibility is that the population that’s getting fatter and the population that’s living longer are actually two very different populations.
Another is that BMI, the statistic that’s being dragooned into service as a surrogate for a measurement of fitness, is peculiarly unsuited to the task. BMI is weight in pounds divided by the square of the height in inches times 703. It has no physiological meaning and was invented by a Belgian statistician to evaluate populations not individuals. It has no verifiable meaning for individuals.
The U. S. population is not stable enough to use BMI to evaluate it. If you don’t believe me, take a look at ethnic makeup of the country in 1980 and its makeup now. The only way such a comparison would tell you anything whatever is if the prevailing physiologies in the population 30 years ago were roughly the same as those of the new immigrants. I have no reason to believe that’s the case.
BMI doesn’t measure fitness or fatness. It’s a function of height and weight and drawing conclusions about fitness or fatness from it makes assumptions about behavior and body type that might well have been true for Belgians a century ago (I have my doubts) but possibly not for Americans today.
Take me, for example. A few years ago I had my lean weight, the weight that I would have with zero body fat, measured. It was 175. Based on my height that meant that even with no body fat at all, no mean feat, I would be overweight by BMI standards. At anything over 10% or 15%, not atypical for a professional athlete, I would be labelled obese.
I wear a 46 jacket and have a 36 waist. I will never be sylph-like. That’s a fact I’ve struggled to accept over the years.
Oooops.
Let me see, taking a measure created specifically to measure populations and taking it down to the individual level. Gee no potential for problem there.
Actually, we use BMI some for determining risk. Most outpatient surgery centers do not take patients above a certain BMI, usually about 45. Above that number the risk of airway complications increases. Many of us are also using BMI for determining management of the morbidly obese. At our institution we do not allow some types of bariatric surgery for a BMI over 60. BMI, in some studies, has also been shown to correlate with longer post-op stays. BMI certainly correlates pretty strongly with incidence of sleep apnea, remembering that there are many non-obese with sleep apnea. IIRC, about 90% of the very morbidly obese have obstructive sleep apnea.
As to the larger point of obesity and disease, I remain surprised that obesity does not show itself as more of a factor in many diseases. I have come to think of it as the problem that complicates other diseases and physiologic problems. It certainly makes invasive treatments more difficult and risky.
Steve
Some years ago I went in for out-patient surgery that turned into major surgery because the chap performing the procedure assumed that my weight was due to fat (which it wasn’t).
Unfortunately, he failed to notify the hospital which proceeded to deal with me under out-patient rules and ejected me (again, under out-patient rules) an hour or so after I woke up.
Your BMI, based on your descriptions, should not be anywhere near 45. I would suspect a newly formed surgicenter or someone who was inexperienced. Weightlifters pose some problems when using BMI as do professional athletes. That is when you should go to more refined assessments like neck circumference or direct examinations. BMI is not perfect, but it has worked out as a pretty easy to use, cheap tool.
Steve