Diet and exercise are the key to a fit body.

But their impact is quite different in boys and girls.

A new British research found that exercise acts differently on body fat for boys and girls. The researchers found that recommendations on exercise to decrease the up-going tendency of obesity in children have tackled with a unisex approach.

The research was made on a random sample of 224 children, 7 to 10 years old at 12 schools in the Republic of Ireland. One in five children was overweight, and 6% were assigned as obese, numbers that are significantly higher than those of other European countries - signal the authors - and the number of obese boys was higher than that of obese girls.

Cardiorespiratory fitness was assessed in all the children, employing a validated running test, and the exercising level executed over a period of four days was investigated on 152. Boys were found to exercise hard twice more than girls. On average, boys spent more than an hour daily for vigorous exercising while girls spent just over half an hour each day. Vigorous exercising was considered running at 9 km per hour or similar energetic effort.

On average, those children who were found to present good levels of cardiorespiratory fitness were significantly leaner and had thinner waists than those whose fitness levels were poor.

The researchers signal that waist size is an important signaling factor because midrift fat is linked to specific metabolic changes, connected to poorer cardiovascular health.

Boys were more likely to be more physically-fit than girls. But the team noticed that hard exercise taken regularly influenced directly only the boys' weight.

And unlike the girls, the boys which exercised the least were the fattest and displayed the thickest waists.

The team also points out the fact that the current measure of body mass index (BMI) could not be used by itself, to determine the extent of cardiovascular risk in children and adolescents of both sexes.