The surprising results were published in the American Journal of Physiology and involved monitoring the weight loss efforts of 60 heavyset but otherwise healthy Danish men.

Half of the men were instructed to exercise for an hour a day, while the other half would sweat it out for 30 minutes. Participants were outfitted with a heart-rate monitor and calorie counter and were told to exercise hard enough to break into a sweat.

On average, men who exercised for just half an hour actually lost more weight than their counterparts, losing on average 3.6 kg in three months, compared to 2.7 kg among those who exercised for 60 minutes.

Among some of the possible explanations for the unexpected results include the fact that 30 minutes of activity presented a less daunting challenge for the participants, which in turn led to increased motivation and, possibly, prompted some to engage in more physical activity beyond the prescribed time span.

On the other hand, those who had to exercise for an hour probably ate more and therefore lost less than their counterparts, scientists postulated.

That theory jibes with a Canadian study published in recent years which found that people have a tendency to grossly overestimate the number of calories they burned through exercise, and then overcompensate for their hard work by eating too much.