Aug. 24, 2012 -- Thirty minutes of exercise a day may be the magic number to lose weight.

A new study shows 30 minutes of exercise a day works just as well as an hour in helping overweight adults lose weight.

Researchers found moderately overweight men who exercised hard enough to sweat for 30 minutes a day lost an average of 8 pounds over three months compared to an average weight loss of 6 pounds among men who worked out for 60 minutes a day.

The overall loss in body mass was the same for both groups, almost 9 pounds.

Researchers say the results are surprising.

Part of the explanation may be that people found 30 minutes of exercise so doable that they had the desire and energy for additional physical activity, says researcher Mads Rosenkilde, a PhD student at the University of Copenhagen, in a news release.

30-Minute Workout Does the Trick

In the study, researchers followed 60 moderately overweight men who wanted to lose weight. The men were randomly put into either a moderate or high aerobic exercise group.

The high-exercise group was instructed to exercise hard enough to produce a sweat, like from running or cycling, for 60 minutes a day. The moderate group only had to sweat for 30 minutes a day.

After 13 weeks, the study showed 30 minutes of exercise a day produced similar or even better results than 60 minutes a day.

The men who exercised 30 minutes a day lost an average of 2 pounds more of body weight than those who worked out for an hour.

Researchers say those who exercised 30 minutes a day actually burned more calories than they should have according to their exercise program.

In contrast, the men who exercised 60 minutes a day lost less body weight relative to the energy they burned during their workouts. The extra 30 minutes of exercise did not appear to provide any additional weight loss in body weight or fat.

More Benefits From Shorter Workouts

Researchers say the results suggest that 30 minutes of exercise a day may provide additional weight loss benefits.

For example, people may still have extra energy leftover after shorter workouts to be more physically active throughout the day.

In addition, researchers say the men who exercised for 60 minutes a day probably ate more to compensate for the longer workout session and therefore lost less weight.

The results appear in the American Journal of Physiology.