Jan. 18, 2012 -- Junk food sales in schools, long blamed for contributing to childhood obesity, do not make a difference overall in the weight of middle school students, according to a new study.
The researchers followed more than 19,000 students from grades five through eight in 1,000 private and public schools.
"What we found basically is, there is no relationship between going to a middle school that sells junk food and gaining weight," says researcher Jennifer Van Hook, PhD, professor of sociology and demography at Penn State University.
The message, she stresses, is not that junk food is OK, but that schools are probably not the main source of kids' junk food intake. The study is published in the Sociology of Education.
However, obesity experts who reviewed the findings for WebMD say that kids need a consistent message about healthy eating.
Junk Food in Schools: A Short History
Public health experts have been concerned about junk food in schools for many years. Obesity now affects 17% of U.S. children and teens ages 2-19, according to the CDC. Advocacy groups have directed efforts at getting junk food out of schools. Some previous studies have found a link between junk food sales in schools and children's weight, although Van Hook says the studies were small and not conclusive.
One scientifically sound study, she says, did show a link between the availability of junk food in school and weight gain in high school students.
Van Hook’s study was what’s called an observational study, which means it cannot prove cause and effect, but only a link or association. Still, she expected to find a link, she says, but did not.
Junk Food in Schools: Focusing on Middle Schoolers
Van Hook and her colleagues looked at data on almost 20,000 children from the National Center for Education Statistics.
It was collected from the 1998-1999 school year, when the students were in kindergarten, until they were in eighth grade in 2006-2007.
The researchers looked at the children's body mass index, or BMI, at the beginning of the fifth grade and again in the eighth grade.
They considered whether the schools offered what Van Hook calls "competitive" food in addition to school-served food. These foods run the gamut from candy and ice cream to low-fat yogurt.
At the fifth-grade mark, 59% of the schools offered junk food. At theeighth-grade mark, 86% did.
The researchers considered race and ethnicity, socioeconomic status, and other factors that might affect unhealthy weight gain.
Children in schools with junk food sales did weigh a bit more by eighth grade than the kids in schools without. However, the difference was slight and not significant from a statistical point of view, Van Hook says.
In the eighth grade, 35.5% of kids in schools with junk food were overweight, while 34.8% of those in schools without it were.