Research in the American Journal of Physiology found that Danish men lost more weight with a half hour of daily exercise than they did with a full hour; their body fat remained the same in both cases. Moderation wins again.
PROBLEM: Creating a negative energy balance -- burning off more than you take in -- is the not-so-secret key to successful weight loss. Dieters, however, often find that eating less triggers compensatory mechanisms, such as increased appetite and a slowed metabolism, that make this balance difficult to maintain. Looking at the other side of this equation, is there an infinitely positive relationship between amount of exercise and pounds shed? Or is there a certain point where the compensatory mechanisms kick in, so that extra time on the treadmill ceases to affect weight loss?
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METHODOLOGY: Sixty moderately overweight Danish men were randomly assigned to either a moderate or high-dose aerobic routine of running, biking, or rowing. The moderate exercisers burned 300 calories per day, which took about 30 minutes, while the high-dose group burned 600 calories, which, predictably, took about twice as long. The subjects' body composition was monitored throughout the 13-week experiment, as were their compensatory behaviors (food intake and non-exercise physical activity). Their accumulated energy balance was calculated from their changes in body composition.
RESULTS: The group that practiced moderate exercise lost an average of 7.9 lbs in body weight, while the group that worked harder only lost an average of 6.0 lbs. Both saw similar losses in fat mass (about 8.8 lbs in the moderate group, and 8.3 pounds in the high-dose group). Researchers measured no significant difference in caloric intake or non-exercise energy expenditure.