The junk food sold at schools does not appear to contribute to middle schoolers' weight gains, a new study says.

In the study, no link was found between children's weight gain and the amount of time between fifth and eighth grade they attended schools that sold junk food, the researchers said. Even transferring from a school that did not sell junk food to one that did did not increase a child's likelihood of gaining weight.

The findings suggest that efforts to combat childhood obesity might best be aimed at parents and the foods available at home and outside of school.

“If we really want to address the child obesity epidemic, we can't solely focus on schools,” said study researcher Jennifer Van Hook, a professor of sociology and demography at Pennsylvania State University. “Schools only represent a small portion of children’s food environment,” Van Hook said.

However, experts say the study does not provide the final word on school junk food and obesity. And regardless of their ultimate impact, the food sold in schools should reinforce the messages of healthy eating that kids are learning in the classroom, said Nancy Copperman, director of public health initiatives at the North Shore-Long Island Jewish Health System in Great Neck, N.Y.

“You'd want to have an environment that was supportive of what they were learning” about healthy eating, Copperman said.

Junk food for sale

While previous studies have looked at the link between food sold in school and childhood weight gain, the new study is the first that includes a nationally representative sample of kids and follows them over time.

The study followed 19,450 children in the United States as they progressed from fifth to eight grade. Children could change schools while in the study, but their new school had to be in the same county.

Administrators at the schools provided researchers with information on whether “competitive foods,” or foods that are sold in competition with the National School Lunch Program, were available at the school through vending machines, snack bars or a la carte. Such foods included junk food, such as soda and candy bars, as well as healthy food, such as nonfat yogurt and bottled water.

Between fifth and eighth grade, the percentage of students who attended schools that offered competitive foods increased from 59.2 percent to 86.3 percent.

Children who moved into middle schools that offered competitive foods were no more likely to gain or lose weight than children who attended schools that did not offer competitive foods. In addition, children who moved out of schools that sold competitive food were no more likely to gain or lose weight than children who remained at schools that sold competitive foods.

The findings held even after the researchers took into account factors that could affect the results, including the students' age, gender, ethnicity, family-income level and the schools' revenue.

The biggest factor influencing children's weight in middle school was how much they weighed when they were younger, according to the study.

Comprehensive nutrition

While the study was rigorous, it did not look at what the children were actually choosing to eat at the schools, Copperman said. Future studies should assess whether the introduction of vending machines at schools changes kids' eating habits, Copperman said.

In addition, while a single factor, such as getting rid of competitive foods at schools, might not make a big difference in terms of a child's weight, it might have a greater influence when added as part of a larger nutrition education program, Copperman said.

“A lot of times when you just take one thing by itself and you don’t put it in to a comprehensive program, you don’t find a lot of effects,” Copperman said.

The new study is published in the January issue of Sociology of Education.

Pass it on: Getting rid of junk food at schools might not have an impact on children's waistlines.

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