30 mins of Exercise a day as good as 60, in some cases.

A new study at the University of Copenhagen in Denmark has found that sedentary, slightly overweight healthy young men, who worked up a sweat exercising 30 minutes daily for three months, lost a similar amount of weight and body fat as those who did 60 minutes of daily exercise.

The researchers describe the findings of their randomized controlled trial in a study reported online recently in the American Journal of Physiology.

The researchers suggest one reason for the surprising result is that the exercise felt "doable" for the participants in the 30 minutes a day group, who even felt afterwards that they could have done more. In contrast, the 60 minutes a day group probably compensated by eating more, therefore losing less weight than expected.

This second point would fit in with the results of previous research that the researchers point to in their background information. This suggests that the reason exercise often produces a disappointing amount of weight loss is because a diet-induced negative energy balance (where calories consumed aren't enough to cover daily energy needs) often triggers "compensatory mechanisms", such as lower metabolic rate and increased appetite.

Perhaps 60 minutes of exercise results in more overcompensation than 30 minutes. On average, the men who exercised 30 minutes a day lost 3.6 kg in three months, and those who exercised 60 minutes a day lost 2.7 kg. The reduction in body fat was about 4 kg for both groups.

The result is significant because 40% of Danish men are thought to be moderately overweight. Overcoming barriers to exercise in a group that does none at all should be easier if the aim is to attain 30 minutes a day than 60 minutes a day.

The study is part of an interdisciplinary trial called FINE, a Danish acronym for physical activity for a long healthy life, which has generated strong data in a group of 60 or so participants.

For the study, the researchers randomly assigned each of 62 healthy, sedentary, moderately overweight young men to one of three groups: a high exercise group (burning about 600 kcal per day with about 60 minutes of aerobic exercise), a moderate exercise group (300 kcal per day, 30 minutes exercise), and a control group that continued to be sedentary.

They monitored the men as they followed their program for 13 weeks.The participants trained every day through the study period. The training sessions were planned to produce a light sweat, but the participants were also instructed to increase the intensity three times a week.

The results showed that body weight went down by 2.7 kg in the high exercise group, and 3.6 kg in the moderate exercise group. Fat mass went down by 4.0 kg and 3.8 kg respectively.