PHILADELPHIA -- In a two-year study involving five Philadelphia elementary schools that replaced sodas with fruit juice and reduced the amount of snacks and candy available in vending machines and the cafeteria, the number of students who gained weight in those schools was half the number of students who gained weight in schools that made no changes in their vending machines and cafeterias.

The study also showed that more than 7 percent of the kids in the five schools became overweight compared to the 15 percent in the schools that did not make any dietary changes.

“That signals to me that we have lots more work to do,” says Gary Foster, director of the Center for Obesity Research and Education at Temple University. Foster also is the lead author of the study, which is published in the April issue of Pediatrics.

The Philadelphia study put to the test a program developed by the Food Trust, a nonprofit organization that works to improve access to affordable, healthy food. Ten schools enrolled in the government-funded study in 2002, and half made the changes.

The study consisted of 1,349 students in grades four through six. About 40 percent of the students were overweight or obese at the beginning of the study. Several of them received free or subsidized meals.

In addition to the changes in schools’ vending machines, students who ate healthy snacks got raffle tickets to win prizes such as bikes and jump ropes.

After two years, the number of overweight students at the five schools dropped 10 to 15 percent, while the number of overweight students at the no-change schools rose a quarter to 20 percent. There was no difference between school groups in new obese students (6 percent) or the overall number of obese students (25 percent).