Exercise for Weight Loss: Take a Hint from Goldilocks

This is the time of year when many folks’ New Year’s resolutions include shedding a few (or a lot) of those excess pounds.  A healthy, balanced diet with proper portion control is the place to start, of course.  And starting an exercise program has tremendous health benefits, even beyond the waistline.  New research suggests, though, that more is not necessarily better — even with something as healthy as physical activity.

Researchers at the University of Copenhagen in Denmark (1) explored the question of the effect of amount of exercise on weight loss.  They looked at overweight sedentary men, dividing them into three groups:

  • a control group (no exercise)
  • moderate exercise (300 calories burned per day, or about 30 minutes of running or cycling)
  • high exercise (600 calories burned, or about 60 minutes per day)
After 13 weeks, they examined weight loss in the three groups.  Not surprisingly, the control group showed no change in weight.  The high-exercise group lost an average of about five pounds — respectable, but actually less than expected, given the number of calories these gentlemen were burning.  But the moderate exercisers actually lost more weight:  about seven pounds on average, or forty percent more than the high-exercise group!  What could account for this Goldilocks effect — not too much, not too little, but just right?
There is one major factor that the researchers did not examine:  body composition.  In other words, how much muscle and fat did each subject have at the beginning and end of the study?  The high exercisers were probably gaining more muscle than the moderate group, resulting in a lower net weight loss.  For this reason, I like to measure body composition (via bioimpedance analysis) at my clinic to more accurately track changes over time.  Lead scientist Mads Rosenkilde admits that if the study extended beyond 13 weeks, the metabolic benefit of increased muscle mass might become more noticeable in the high exercisers.
Nevertheless, there are at least two major pitfalls that the researchers identified for the high-exercise group.  The increase in calories burned seemed to lead to a compensatory increase in food intake — this was most likely unconscious, a result of altered hormonal control over hunger signals (the set point theory).  A unique aspect of this study is that the subjects were equipped with motion sensors, to record their physical activity outside of the formal exercise periods.  The high exercisers were actually more sedentary the rest of the day compared to the moderate group — perhaps due to fatigue, or perhaps they just felt they “deserved” more rest.
This study gives us plenty of food for thought on physical activity.  But like everything, let’s take it in the context of all research, not just the latest headline:
1.  Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise–a randomized controlled trial in overweight sedentary males.   2012 Sep 15;303(6):R571-9. doi: 10.1152/ajpregu.00141.2012. Epub 2012 Aug 1.
2.  Just HIT it! A time-efficient exercise strategy to improve muscle insulin sensitivity.  J Physiol. 2010 September 15; 588(Pt 18): 3341–3342.

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