Exercise vs. calorie restriction: head-to-head match-up


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- Alex Hutchinson (@sweatscience)


Fitness or fatness: which is more important in determining your health? As I discussed in this Jockology article, some researchers (most notably Steven Blair at the University of South Carolina) believe that most of the health problems we associate with obesity are actually a consequence of poor aerobic fitness. In other words, they argue, it’s okay to be a little portly as long as you’ve exercised enough to have good endurance.

This challenges the basic tenet of old-school, keep-it-simple nutritional thought — that good health is simply a matter of matching the calories you eat to the calories you burn. Can your body tell the difference between a calorie burned through exercise and a calorie avoided through dieting? Well, a really interesting and excruciatingly careful study from researchers at Louisiana State University has just tackled this question.

calorie-restrictionHere’s the gist: 36 moderately overweight subjects, divided into three groups. One group was the control, and stayed exactly the same during the six-month study. A second group cut their calorie intake by 25 percent, while the third group cut calories by 12.5 percent and increased calories burned through physical activity by 12.5 percent.

As expected, the two intervention group lost exactly the same amount of weight (about 10 percent of their total), and they both shed roughly the same amounts of total fat and visceral fat. This makes sense, because they were both operating under identical calories deficits. Here’s the rub, though: only the exercise group had significant improvements in insulin sensitivity, LDL cholesterol and diastolic blood pressure.

This tells us that a calorie is not just a calorie — it matters how you cut calories. And, as Steven Blair is constantly pointing out, being thin is no guarantee of health if you’re not active. (And, as a nice bonus, it also tells us that it’s possible to drop 10 percent of body mass through a combination of diet and exercise — though it probably helps to have a team of researchers cooking your meals and supervising your exercise!)

4 Replies to “Exercise vs. calorie restriction: head-to-head match-up”

  1. A couple of comments. One, it turns out that participants followed a diet based on the American Heart Association Step 1 recommendations. Low-carb or paleo/primal folks would argue that you would likely see benefits in risk factors for metabolic syndrome by reducing carbs, especially grains and sugar. So I agree … a calorie is not just a calorie!

    Also, I guess that’s a tilda (~) on the ~10% on the right of the graph since 10% is actually at zero on the y-axis.

    Anyways, I’m fully in support of the importance of exercise for health, but tend to think diet is also important … especially wrt weight loss.

  2. Thanks for the comments, Beth. To your first point — yes, they followed the AHA diet, which obviously comes with its own set of questions. From the point of the view of this study, the “good” news is that the control group didn’t experience any significant changes. That doesn’t answer any questions about low-carb versus high-carb, but at least it avoids confounding the comparison they were trying to make between avoiding calories and burning them. (The use of the AHA diet, as I understand it, was primarily to ensure that the subjects were eating a roughly similar diet, not because they were assuming it’s “best.”)

    As for the 10%, I was a little confused by that too. In the text (and the graph, as you noted), they describe the weight loss as [tilde] 10% without giving specific numbers. I agree the graph looks more like 8%. I guess they were rounding to one significant figure or something.

    And I couldn’t agree more about the importance of diet — it’s certainly a crucial component. Call it a necessary but not sufficient condition. The authors of the paper make this point too, in part because the changes in HDL cholesterol and systolic blood pressure were roughly the same in all three groups. (I suppose you could argue that the 9% increase in HDL in the control group shows the benefits of the AHA diet, but let’s not go there!) Here’s the paper’s concluding paragraph:

    “Results of the current study suggest that beyond changes in fatness, combining CR with exercise is important for increasing aerobic fitness and optimizing improvements in risk factors for diabetes and CVD, including improved insulin sensitivity, LDL cholesterol, and diastolic blood pressure that are beyond those of body weight/body fat reduction alone. Improvements in other cardiometabolic risk factors, however, such as systolic blood pressure and HDL cholesterol might only be associated with changes in fatness and/or consumption of a healthy diet.”

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