The studies led by Dr. Catherine Davis, clinical health psychologist at the Medical College of Georgia, were conducted on about 200 overweight, inactive children in the age group of 7-11years.
In the study all the participants learned about healthy nutrition and the benefits of physical activity.
Out of all the participants, one-third exercised 20 minutes after school and another third exercised for 40 minutes. Children played hard, with running games, hula-hoops and jump ropes, which raised their heart rates to 79 percent of maximum, which is considered vigorous.
The analysis also showed that a regular exercise program reduced body fat and improved bone density in the kids.
"Is exercise a magic wand that turns them into lean, healthy kids? No. They are still overweight but less so, with less fat, a healthier metabolism and an improved ability to handle life," Dr. Davis said.
The working of the brain shown by Functional magnetic resonance imaging studies, were performed on a percentage of children in each group.
The analyses found that those who exercised had different patterns of brain activity during an executive function task.
"Look what good it does when they exercise. This is an important public health issue we need to look at as a nation to help our children learn and keep them well," Dr. Davis said.
"Regular exercise may be a simple, important method of enhancing children's cognitive and academic development. These results may persuade educators to implement vigorous physical activity curricula during a childhood obesity epidemic," researchers said.
"Aerobic exercise training showed dose-response benefits on executive function (decision-making) and possibly math achievement, in overweight children," they added.
By observing the children's insulin resistance, a precursor of type 2 diabetes in which it takes more insulin to convert glucose into energy, it was found that levels dropped 15 percent in the 20-minute exercise group and 21 percent in the 40-minute group.
However, the control group stayed about the same.
"Increasing volume of regular aerobic exercise shows increased benefits on insulin resistance in overweight children, indicating reduced risk of type 2 diabetes, regardless of sex or race," researchers said.
To quantify bone, tissue and fat, DEXA scanning was used to accurately assess body composition using a small amount of radiation.
"If physical education were ideal, which it's not - it's not daily and it's not active - then children could achieve this within the school day," Dr. Davis said.