In-class exercise programs may not be helping children to shed excess pounds but the activities still carry health benefits, say researchers who weighed the evidence.

In Tuesday's Canadian Medical Association Journal, researchers with the BC Children's Hospital and Vancouver General Hospital analyzed 18 previous trials involving 18,141 children who either received a school-based physical activity program or were in a control group that did not.

Dr. Kevin Harris and his colleagues found no reduction in body mass index, one measure of obesity, among children in the activity programs.

"They're unlikely to have a significant effect on the obesity epidemic that we're seeing in children today," Harris said.

In the 1970s, in a classroom with 20 students, one child would be overweight or obese, but today there are five.

The exercise programs are meant to get students moving in class.

"It is 20 minutes of sustained activity, meaning that you need to be able to raise the heart rate for the kids," said Martin Buschbeck, a Grade 6 teacher at Ormiston Public School in Whitby, Ont.

The studies had some limitations, since the researchers didn't measure how much activity the children got, and there is disagreement over whether BMI is the best way to measure obesity.

Broaden approach to tackle child obesity

The causes of obesity are complex, and it's an oversimplification to say it's caused by too little exercise or poor diet alone, Harris said.

The researchers don't want the study to discourage school activity programs.

"I think it's extremely important to note that school-based physical activity has a number of beneficial health effects including improved cardiovascular health and improved bone health, and it should be promoted for these reasons," Harris said.

In a commentary that appears in the same issue, Louise Baur, who specializes in children's health at the University of Sydney in Australia, said reversing trends in child obesity requires a broader, long-term approach that includes:

• Healthier school meals.
• Subsidies on fruits and vegetables for schools and daycares.
• Changes in urban planning so cities encourage more physical activity.

School-based physical activity also reduces blood pressure, increases lean muscle mass, and improves flexibility, the researchers said.

Children gain other benefits, too, said Antony Card of Memorial University's School of Kinetics and Recreation in St. John's.

"They change their aerobic capacity, their flexibility, and just general health and of course there's an impact on learning as well."

Fighting obesity also involves nutrition and psychological help, Card said.

Buschbeck said that he's noticed that in his class, the exercises have helped the health, learning, and behaviour of students.