Surprising New Findings on Obesity

One of the first Freakonomics Radio podcasts we made was an episode about the (surprisingly tenuous) link between obesity and health problems. A new study in The Journal of the American Medical Association finds that “Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality.”  Writing for The Daily Beast, Kent Sepkowitz explains:

Compared to people with a normal weight (a BMI less than 25), the overweight (BMI between 25 to 30) had a 6 percent lower mortality rate—and both groups had a rate about 15 percent lower than the obese, especially the very obese (BMI above 35).

The explanation for the finding is uncertain. Perhaps the pleasantly plump but not obese have an extra reserve—a literal spare tire—that confers a survival advantage should they become seriously ill, whereas the lean-iacs do not. Or maybe the thin ones were thin because of a serious illness that, in the course the various studies, killed them. Or maybe the thin ones were thin because they were chain smokers living off Scotch and potato chips. Or just maybe the occasional pig-out does soothe the soul and make for a happier, healthier individual.

(HT: Andrew Sullivan)

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  1. Scott Templeman (@tallbonez) says:

    Real findings should be that BMI is a garbage metric

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    • Scientistbymistake says:

      I couldn’t agree more about BMI being a grabge metric.

      I am a triathlete, and in a recent medical at my company, the nurse exprerssed concern about my low BMI, after remarking on my powerful sounding heart and spectacular peak flow measurement. I am built like a whippet, am uber-fit and extremely healthy.

      The next guy in after me was a 230 pound bodybuilder, really fit, ripped as anything but only 5’10″, guess what?…

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      • bob says:

        We have the same problem at my office. Except every other person is morbidly overweight and many are struggling with diabetes.

        If you bring up any simple measure of obesity (like BMI), they all point out how it’s a junk metric and it doesn’t address their muscle mass. I wonder if they could do a single push-up.

        BMI is pointless. Fit people know that at best it’s a weak guideline. Fat people dismiss it because they don’t want to change to a healthier lifestyle. Rarely do you meet a person who actually wants to know what their healthiest weight would be and then change their life to achieve it.

        As a person who is constantly trying to live healthier, I’d love to have an ideal weight for my height and build. I’m 5’11″ and 167 lbs, and I meet the BMI guidelines, but I’d love to know whether another 10 lbs either way would extend my life (and it’s quality) or reduce it.

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      • James says:

        At 6′ and ~200 lbs (and a 32″ waist), I’m fit but hardly a hardcore bodybuilder, yet by BMI I’m in the marginally overweight group. I wouldn’t be surprised if people like me, slightly overweight by BMI, but carrying the “excess” weight as muscle rather than fat, have skewed the results of this study.

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  2. NC says:

    Or maybe the study included people with terminal cancer and other diseases which cause them to lose weight. This would be a very poor study indeed. And a source of incorrect information about the health risks of being overweight.

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    • Enter your name... says:

      The combined studies covered nearly 3 million people long enough that almost 10% of them died during the tracked time period. I think it was probably a pretty good study overall.

      I understand that they excluded anyone in hospice care or in the hospital at the start of the study. It probably does include people with eating disorders like anorexia nervosa (known to have a high mortality rate among young adults), though; on the other hand, it probably includes a lot more people with binge-eating and other disorders that cause weight gain.

      It is also true that most of the excess mortality in “healthy weight” people comes from the people whose BMI is in the skinnier half of that category. I think it is probably a good basis for us to consider whether the BMI categories need to be adjusted slightly, so that “barely heavy enough to be normal” is now considered “underweight”.

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  3. Paul says:

    Is it also possible that the use of BMI as the gauge for obesity is outdated? It doesn’t measure muscle mass or fitness level. I understand it was used in this particular study for comparisons to other studies, but it seems to me that BMI is misleading at best.

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    • Tomasz T. says:

      It’s true that BMI cannot distinguish between a plump couch potato and muscle-packed bodybuilder, but I would guess the number of these latter guys is so minuscule compared to the former, that they cannot disturb the results too much. BMI may be a very good proxy for overweight/obesity at a population level, even though it can be wildly wrong for a particular individual.

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      • Paul says:

        Using BMI to determine “weight” is like using horsepower to determine how fast a vehicle can go. I’m sure there are some relatively close relationships, but when it comes down to it, there are so many other aspects that should be taken into consideration before drawing a conclusion.

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      • Enter your name... says:

        I think you meant to say “using BMI to determine body composition”. To determine “weight”, one normally uses a scale.

        BMI doesn’t work well for individuals, but it is a reliable and validated method for evaluating large populations. There simply aren’t that many “overweight” bodybuilders in large populations, so their contribution to that category is dwarfed by the ignorant men who think that their 48-inch waistlines are “solid muscle” because the fat is located behind the thin abdominal wall (a far more dangerous place for fat to accumulate) and thus doesn’t visibly jiggle.

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  4. Djyrn says:

    How long until insurance companies start dropping premiums for higher BMI’s?

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  5. Doug says:

    Perhaps BMI is a terrible way to measure healthy weight. This has been well insinuated by a number of beyer weight and health professionals.

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  6. Jen says:

    Yup, there are a lot of very fit people who are in the 25-28 BMI range. BMI doesn’t take muscle mass vs. fat mass into account.

    When you have a selection of fit, muscular people being called overweight and have likely not weeded out the very sick, alcoholics, anorexics, etc. from your below 25 BMI, that may well explain the “advantage.”

    It may still indicate that some extra weight isn’t actually harmful though.

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  7. Jessica says:

    Not just the use of BMI, basically this whole “study” was full of garbage methodology. We are so desperate to continue living our crappy lifestyle that we’ll allow anything to pass for science if it gives us hope.

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  8. Bridget says:

    Even if we decide that the method for calculating BMI is reasonable (which I’m not sure it is), the ranges for what is considered “normal” vs “overweight” seem a little skewed to me. I have friends who I don’t think for a minute need to be concerned about weight loss, who live healthy lifestyles and everything, they’re just not model skinny, but they are technically in the “overweight” range. Maybe this study is just showing that those ranges are a little off, and the upper limit for “normal” should be raised a little bit, because those weights are actually still healthy.

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    • James says:

      It’s not so much that the BMI ranges are off, as that it was designed to measure a mostly sedentary population. As a consequence, there’s a part of the range from high “normal” to moderately overweight in which the excess weight can come from either fat or muscle. BMI can’t really distinguish between the two groups, so you’d have to apply some other measure – say chest to waist ratio for men.

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