Fitness vs. fatness, again


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Another study weighs in on the question of whether fitness or fatness is a more important marker of health (abstract here, press release here). This is a nice, clear one. The researchers followed 14,345 men (with an average age of 44 at the start of the study). They did two detailed physical exams just over six years apart (on average), then followed the men for another 11 years to see which ones died, and why.

Basically, there are two variables of interest:

  1. Did the men lose weight, gain weight, or stay stable between the two exams?
  2. Did the men lose fitness (as measured by a maximal treadmill test), gain fitness, or stay stable?

The result: those who maintained or improved fitness were less likely to die by ~30-40% compared to those who lost fitness — even when you control for factors like BMI. Obvious and expected.

But what about weight? As you’d guess, those who gained weight were more likely (by 35-39%) to die of heart disease than those who lost weight or stayed stable. BUT if you take into account changes in fitness, then the effect of changes in weight almost disappeared. So this is further support for Stephen Blair’s argument that it’s fitness that matters, not fatness, when it comes to predicting health (and Blair is, indeed, one of the authors of this paper). As the press release puts it:

“This is good news for people who are physically active but can’t seem to lose weight,” said Duck-chul Lee, Ph.D. […] “You can worry less about your weight as long as you continue to maintain or increase your fitness levels.”

But let me add one clarification. Whenever this topic comes up, I often hear from people who say something along the lines of “See, BMI is meaningless! This proves that doctors should never even measure weight, because it doesn’t predict health.” Not quite. Let me reiterate: those who gained weight in this study were 39% more likely to die of a heart attack than those who lost weight. The reason weight gain doesn’t stay as an independent predictor of death is that those who gained weight also (on average) lost fitness, and those who lost weight also (on average) gained or maintained fitness.

So the very important message that this study reinforces is that it’s fitness that matters most. Keep exercising even if you don’t see changes in your weight, and you’ll be gaining extremely important benefits. But don’t interpret it to mean “it doesn’t matter if I gain weight, because weight is meaningless as a health marker” — because there’s a decent chance (though it’s certainly not guaranteed) that if you’re gaining weight, you’re also losing fitness.

(One final caveat: as the press release notes, 90 percent of the men were either “normal weight” or “overweight” — i.e. BMI under 30. So you can’t assume that the same lack of problems would hold true for the “obese” category with BMI over 30.)

6 Replies to “Fitness vs. fatness, again”

  1. As you said, nice clear study outlining the importance of regular exercise to improve/maintain fitness, irrespective of what the scales are telling you. Thanks for posting and the excellent breakdown.

  2. Somewhat related to what you are saying Alex, you cannot treat fitness and weight as independent variables. Yes, there maybe parts of each that are somewhat unpredictable given the other (for example, you may at one point in time gain a little fitness and not be losing weight as you may be going through a period of muscle growth, or you may be thin, as hard as that may be to imagine in this day-and-age, and gaining could help fitness). But for those that are overweight it is impossible to separate the variables. In fact, a treadmill test, in general, is going to be easier and therefore report as being more fit if you go from a BMI of 30 to a BMI of 27.

    In the end, if you are truly getting more fit (and coming from an overweight situation, like 95% of North America these days), you are losing weight, or at least losing body fat.

  3. I think maybe this is about muscle. Maintaining muscle as you age is critical. It is probably more important than gaining a bit of fat. Loss of muscle means loss of function, as well a very negative metabolic changes. The weaker you are, the harder your heart has to work just to walk and do daily activities, The less glucose storage you have, etc..
    And weaker people tend to move around less, so they get even fatter, so it’s a vicious cycle.
    Strength is good.

  4. @Griff

    True. The ACSM also published their 2012 fitness trends survey a couple of weeks ago and strength training for older adults came in at the second spot of the top ten list.

    In my opinion, that is a positive development.

  5. The same author did a study in ’99 that had more obese people, the results were the same, if you pass the fitness test you’re good, if you don’t, not so much, but like 95% of the skinny people passed the fitness test, so you can’t treat weight as meaningless so much as you can address the problem of weight in an additional way (and one that may be more successful, given how many people fail to keep weight off).

    Full study:

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