At the end of the study, researchers found that the then-eighth-grade students in intervention schools who had been overweight or obese in sixth grade had a 21 percent lower rate of obesity than their counterparts in comparison schools. Students at intervention schools also had lower average levels of fasting insulin and smaller average waist circumferences.

Surprisingly, the number of overweight and obese students declined in both intervention and comparison schools. Additionally, the study groups did not differ in mean glucose levels or the percentage of students with elevated fasting glucose in the overweight category.

"Although more research is needed to better understand why all schools showed improvement, a possible explanation is that comparison school parents were informed of their children's risk and may have made healthy changes on their own," Cooper said. "Plus, comparison schools volunteering to be in the study did so out of concern for the health of their student body and may have later made independent changes in the school environment."

Over the course of the study, intervention schools provided students with low-fat, high-fiber foods and more fruits and vegetables, with an emphasis on water, low-fat milk and drinks with no added sugar. These students also had longer, more intense periods of physical activity - defined as achieving a heart rate of at least 140 beats per minute, with a target of 150 minutes or more of such activity every 10 days. And they were involved in highly interactive, small-group classroom activities and awareness campaigns promoting long-term healthy behaviors.

Source: University of California - Irvine