SUNDAY, June 27 (HealthDay News) -- School-based efforts at better nutrition, more exercise and improved education about healthy living can help kids who are most at risk for obesity keep the weight off, compared to children in schools without such programs, a new study suggests.

But the program failed to reduce the overall numbers of overweight and obese schoolchildren -- those numbers fell by 4 percent over three years whether the 42 middle schools in the study had such initiatives or not, the researchers report.

"The intervention, surprisingly, did not result in a [population-wide] reduction in overweight or obesity," said lead researcher Gary D. Foster, a professor of medicine and public health and director of the Center for Obesity Research and Education at Temple University, Philadelphia. "What's surprising is that the control group improved as well," he said.

The school-based initiative didn't seem to have much of an impact on children who were not already overweight or obese by sixth grade, the team found, but it did impact children who were already having weight troubles by that grade level.

For those kids, "there were small [weight-loss] effects of about 3 percent. Although that's small, it's enormous given the rates of obesity in this country," Foster said. "This was an unexpected but fortunate finding -- that we are actually impacting the kids at the greatest risk."

The findings are slated to be presented Sunday at the annual meeting of the American Diabetes Association in Orlando, and they are also being simultaneously published online in the New England Journal of Medicine.

For the study, Foster's team randomly assigned more than 4,600 students from the 42 schools to a diet, exercise and information program, or to a program where only their weight and height was assessed. The study targeted schools with high levels of minority children, because studies have shown that they are at especially high risk for obesity.

Children in the program were offered healthier food choices throughout the school: in the cafeteria, at snack bars and in vending machines, and during class events. These included: lower-fat, higher-fiber foods; more fruits and vegetables; and an emphasis on water, low-fat milk and drinks with no added sugars.

In addition, there were longer, more intense periods of physical activity for the schoolchildren, and activities and awareness campaigns to promote healthy living.

The researchers found that children who were already obese at the start of the program lost a significant amount of weight, as indicated by reductions in waist size, compared with other children.

In fact, children in program schools who were either overweight or obese in the sixth grade had 21 percent lower odds of being obese by the end of eighth grade, compared with students in schools without such initiatives. The program also lowered levels of fasting insulin, a key indicator for diabetes risk, the researchers found.

However, children from both types of schools had the same average blood sugar levels and the same percentage of students with elevated blood sugar, the study authors noted.

Foster said that it is intriguing that the rate of overweight and obesity dropped by 4 percent regardless of whether the school had an anti-obesity program in place or not. "This is potentially good news -- that the rates of childhood obesity appear to be declining [naturally]," he said.

Several factors may be at work in this decrease in overweight and obesity even among those children, Foster noted, including children putting more attention on their weight. Just the fact that the researchers were measuring children's height and weight might have made the youngsters more weight conscious, he added.

"Something has changed and we've got to figure out what that something is," Foster said.

Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine said that "the results of this study are open to interpretation, and thus conclusions are apt to reside in the eyes of the beholder."

People who don't put much stock in school-based interventions will point to the lack of an effect overall, he said. "However, those who perceive value in school-based interventions -- and I am among these -- will focus on the obvious pattern in an array of secondary outcomes, including reductions in body fat and insulin levels, which in turn would be expected to reduce diabetes risk," Katz said.

And the program's effect on obese children is important, Foster said.

"There is a strong signal here that this [program] can make a difference," Foster said. "If we can reduce the risk of type 2 diabetes in children by reducing the rates of obesity and reducing waist circumference, that's an important outcome," he said.

More information

There's more on childhood obesity at the U.S. National Library of Medicine.