A series of interactive computer exercises designed to encourage healthy eating and physical activity didn't help keep middle school students from gaining extra weight, according to a study in the Netherlands.

The study, which involved close to 900 students and was published in the Archives of Pediatrics & Adolescent Medicine, said the program did lead to short-term improvements in the number of sugary drinks and snacks the children consumed, but was probably too brief to change habits over the long run.

"The ... intervention was associated with positive short-term effects on diet but with no effects or unfavorable effects on physical activity and sedentary behavior," wrote Nicole Ezendam, who was with the Erasmus University Medical Center in Rotterdam when the study was conducted.

The study, conducted at 20 schools in the Netherlands, had half of the roughly 900 12- and 13-year-olds involved act as a comparison group, while the rest completed eight computer sessions over a few months.

Each session was on a different health topic, including sugary drinks, fruits and vegetables and sports participation. They taught the children about the benefits of eating better and exercising more, and included a survey on their own health habits and whether or not they wanted to improve them.

The program then helped them create a plan on how they would make positive changes and who would support them.

After four months, children who had gone through the program reported drinking fewer sugary drinks and eating fewer snacks, and slightly more vegetables, than children who didn't. But in general, there was little difference in how much exercise students got after completing the web exercises.

Two years later, a similar number of children in both groups, between 16 to 18 percent, were overweight or obese. There was also no difference in their average body mass index, a measure of weight in relation to height, or the size of their waists.

Ezendam said that the students didn't have additional reminders of the information they learned in each session and might not have had a supportive environment in which to make healthy changes, such as more school gym classes or better cafeteria food.

Other experts agreed that while the concept of web-based programs had potential, it alone was not enough—and may need to last longer.

"I think to increase the efficacy of these types of interventions it's important to continue to be engaged in it beyond eight (sessions), so you learn the skills and techniques and stay motivated," said Mia Lustria, who studies web interventions at Florida State University in Tallahassee but wasn't involved in the study.

"The results are quite encouraging. Health behaviors to begin with are very hard to change."

Another approach may be to develop mobile apps that give children up-to-the-minute feedback on what they're eating and how much they're exercising, said Gary Bennett, who studies obesity prevention at Duke University.

"Engagement is really the name of the game," he added.