Fat Makes a Comeback

April 20, 2005 | 13 comments
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The CDC is airing its dirty laundry this week, as a new report comes out claiming that last year’s CDC report on obesity is basically hogwash. In the old numbers, obesity was this bomb descending on America that was going to wipe us out. It claimed that obesity caused 400,000 deaths/year, making it the number two cause of death. Thus, obesity wipes out the equivalent of Utah Valley every year.

Not that Utah Valley is particularly fat, I’m just giving a hypothetical.

The new report, issued by another division of the CDC, uses more recent data and pays more attention to statistical problems. They find that there are about 25,000 obesity caused deaths. So it wipes out, I don’t know, most of Palo Alto each year. This is a 14-fold downward revision. And just to rub salt in the wounds, they find that being classified as underweight causes slightly more deaths than those caused by being overweight. Don’t you hate it when that happens?

The new report also finds that having a slightly higher BMI predicts better long term health (don’t miss the graphic on this one!). Of course, this optimal BMI is technically in what is now the “overweight” range, which makes one wonder what it means to be overweight. Apparently, it means you live too long… This is called “the obesity paradox” by one source. Well, I suppose the world is full of paradoxes for some people.

Next year, the other half of the CDC might come out with a new report slamming the old one, as some people are quite convinced that obesity is an epidemic. But I just wanted to take a moment to chuckle at the audacity of it all. Researching the mortality effects of obesity is incredibly difficult. The research designs, even when done as well as possible, leave a great deal to be desired because they cannot control for so many important unobserved differences. So it is, I think, incredibly important to be up front about these limitations.

Besides the unobservables, how do we think about competing risks? You see, everybody (well, almost everybody) dies. The only question is, what will get you first? Thus, suppose I define a carcinogen as something that increases your chance of dying from cancer. Well then, bypass surgery is a horrible carcinogen. By stopping you from dying of heart failure, it massively increases your risk of dying from something else. Now, this is not my field, but similar issues come up in economics, and it’s a real pain to try to deal with in a compelling way.

There are lots of people out there who have been convinced that we have scientific proof of some favored proposition, only to have their faith dashed against the rocks of new data or new methodology. We do the best we can, but the arm of flesh, statistically speaking, has low power. Not that I’m all that impressed with the non-empirical academic approaches either. We, as a people, may not be great at getting revelation, but we’re not so hot at other methods of finding truth either!

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13 Responses to Fat Makes a Comeback

  1. J. Stapley on April 20, 2005 at 11:44 am

    While there is currently a difficulty in determining mortality rates associated with obesity. There is no question that obesity dramatically increases onset of diabetes, heart disease and some cancers.

  2. Frank McIntyre on April 20, 2005 at 11:47 am

    J.,

    Correlation or causation? In any case, the results were not that nobody died, just that the deaths, if one accepts the new study, were blown way out of proportion. Nor am I claiming, as should be obvious, that the new numbers are “truth”.

  3. Jared on April 20, 2005 at 1:10 pm

    Your point is well taken, though perhaps a little overly pessimistic, IMO. It is easy to see why the public may, at times, feel jerked around by science (or the reporting of it, anyway).

    My advice: Don’t build your theology around isolated prophetic statements, and don’t live your life according to the latest study. Look for broad agreement and use some common sense.

  4. Derek on April 20, 2005 at 1:22 pm

    The Body Mass Index (BMI) has some pretty serious limitations. People will indiscriminately lose not only fat but also beneficial muscle just to lower their BMI.

    Really, it’s % body fat you should be measuring.

  5. Doc-Kwadwo on April 20, 2005 at 3:08 pm

    Amen, Derek.

    One of the guys in my med school class has a BMI well into the range of dangerous… until one considers that he has single-digit body fat percentage and it one of the fittest men at the university. Muscle is heavier than fat, so his BMI soars. Not that he cares.

    BMI has huge limitations, BF% is the way to look at the issue. Alas, it is harder to accurately measure, so it gets short shrift. Even the military, which attempts to use BF% to determine fitness standards, resorts to neck/waist ratios and other such less-accurate means of measurement.

  6. Ivan Wolfe on April 20, 2005 at 7:23 pm

    I hate BMI. My body fat is at a respectable 13-15% (depending on when the measuring is done and how it is done). I lift weights 3 times a week and walk 4-5 miles a day.

    Yet according to the BMI charts, I am not just obese, but “morbidly obese.” My ideal weight, according to BMI, is 187 – something I have not weighed since my freshman year in high school.

    Is it possible the “obesity” epidemic is actually a health craze and more people have higher BMIs because they exercise?

  7. Mark N. on April 20, 2005 at 10:33 pm

    Sounds like it’s time to come to terms with the fact that most “news” we’re fed these days is a load of horse puckey, which load we can certainly do without. We’re probably better off canceling the subscription to the newspaper, tuning out CNN and Fox News, and time to start reveling instead in our uninformedness.

    From the news organizations’ point of view, they probably consider their reports to be highly accurate. If only they would learn to question the “facts” that they’re being fed.

  8. Becky on April 21, 2005 at 11:02 am

    Sure the BMI has problems, mostly because everyone is trying to use it for something it was not originally for. All it does is says at what range of height/weight ratio you are most/least likely to die. Simple correlation. No, it doesn’t control for body fat %, family history, VO2 max–it doesn’t know if you are in shape… I agree, the statistics are terrible, and yet, do you really need some ideal, well statistically crafted number to tell you that Obesity is a problem in this country, and quickly becoming more of one? And while Obesity itself may not be a direct cause of Heart Disease, type II Diabetes, etc, isn’t it enough that it is a strong instrumental variable for predicting such disease? That the by products of loosing extra weight generally involve changing actual lifestyle patterns that lower the risk for such Disease?

    To Ivan I would say, no–it is definitely not a health craze…very few people exercise to such an extend that they put on so much muscle that it is causing them to be in the obese category…and even if they do, such extreme muscle mass is actual detrimental to your health to some extent, simply by the extra strain carrying around such a lot of weight can put on your heart… (Although come to think of it, I wonder if they controlled for steroid use in that study???)

    Finally, I want to mention a recent study done by some economists for the state of California about how much Obesity costs California each year, not just in terms of health care, but also in terms of lost productivity… the numbers were staggering…apparently about 22 billion in 2005…

  9. Frank McIntyre on April 21, 2005 at 11:23 am

    Becky,

    If it is not causal, it is not causal and there is no use treating it causally. In which case one should quit talking about obesity and talk about good cardiovascular health. So yes, if people reduce their fat by exercising, that may be good for them, but it still is no excuse for confusing the benefits of exercise with those of less obesity. And yes, we do need statistics to tell us whether or not obesity is a mortality problem. It is not at all clear why fat, in and of itself, must be bad for life expectancy.

    That said, obesity, all by itself, may well have a causal effect on health. I don’t know. But I have yet to see much evidence about how much death it actually causes (as opposed to how much death it is correlated to).

    The study did not control for steroid use. I am doubtful it even controlled for exercise. The study in California probably uses the same problematic methodology and then puts it in dollar terms, perhaps to encourage (ill-advised) policy action. But putting lipstick on a pig won’t make it any prettier.

    Well, maybe it will make it prettier, I don’t know. I’d have to see the pig.

  10. Becky on April 21, 2005 at 1:21 pm

    First of all, I never specified that fat was a mortality problem, yes we do need statistics to tell us that, I said that Obesity is a problem period. People, when they are Obese get tierd more easily (you would too if you were carrying that much weight around), the safety restraint systems in their cars are more likely to fail, they are more likely to suffer from bad knees and hips (carrying that much extra weight around simply does that to you). it is a problem.

    Perhaps you think that a “negative impact on life expectancy” is the only important effect of Obesity, and if it is not proven then we all might as well “let the soul delight in fatness” but I argue that there is a quality of life issue at stake as well. I suppose that you can argue that not everyone cares if they can play pickup soccer, go out for a run, or even walk up a flight of stairs without being out of breath, and I suppose that is true. But most people would prefer to be able to do these things, whether they do them in reality or not. Optionality is always valuable.

    With respect to the study I referred to, it was the one that found that muscle mass increased the mortality due to heart failure (I’m not sure if this was clear).

    Finally, I couldn’t find the link just now, but when the California study came out I looked at the actual write up (as I too am always suspicious of the statistics in studies) but the methodology in this study actually looked surprisingly good.

    taking this out of the arena of statistics, Frank, I would like to ask you personally, do you believe that it is possible to be obese (not just a little fat, or “obese” by the BMI by virtue of having too much muscle–but truly carrying a huge body % of fat) and at the same time healthy? (Define healthy as you like). I am interested to know…

    Meanwhile, I don’t know about lipstick alone, but a really good makeup artist can do wonders…

  11. Frank McIntyre on April 21, 2005 at 3:37 pm

    I don’t have any problem with saying that being truly obese is a quality of life problem. I am just talking about the mortality numbers. My point is that it is not clear at all that obesity by itself has important repurcussions for one’s life expectancy.

  12. Mark Martin on April 21, 2005 at 5:24 pm

    #3: “It is easy to see why the public may, at times, feel jerked around by science (or the reporting of it, anyway).”

    #7: “Sounds like it’s time to come to terms with the fact that most “news” we’re fed these days is a load of horse puckey, which load we can certainly do without.”

    For anyone who would like to sharpen their skills at carefully questioning and analyzing science and news reports, I recommend the book “News and Numbers” by Victor Cohn.

    It’s easy to become cynical and dismiss all reports. However, some are quite useful, so as consumers it’s good for us to learn to decipher the difference.

  13. seven bohanan on April 21, 2005 at 6:20 pm

    Fat folks are everyone’s favorite target. Of course, no sensible person would contend that morbid obesity is good for the body (or mind for that matter). The current BMI and CDC guidelines, however, are not only unworkable and false, they are intolerant. They are born out of misinformation, disgust, and vanity, and they lead to frustration, surrender, and ambivalence. It is not a coincidence that the (relatively) new BMI comes at a time when the dissemination of exceedingly thin actors and other celebrities (especially women) is unrelenting.

    How many suicides are attributable to body dysmorphia or depression founded in body image issues?

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