Researchers were so surprised by this finding that they held it out of publication for two years, but it turns out that access to junk food in middle schools didn't affect the weight levels of students.
Jennifer Van Hook and colleagues at Penn St. University used an existing federal dataset that tracked the behaviors of nearly 20,000 children from kindergarten in 1998 to eighth grade in 2006. The data showed an increase from fifth grade to eighth grade in the share of students who attended schools that sold junk food. But over the same timeframe, the share of students who were overweight or obese actually declined from 39.1 percent to 35.4 percent.
“We were really surprised by that result and, in fact, we held back from publishing our study for roughly two years because we kept looking for a connection that just wasn’t there,” Van Hook said. The study was published in the January issue of Sociology of Education.
The study presents a paradox for school and public health officials. In Minnesota, millions in state public health grants have been spent on reducing junk food consumption in schools and increasing access to fresh produce and healthy snacks and meals. (However, it should be noted that the emphasis of these Statewide Health Improvement Grants wasn't to eliminate junk food, but rather to expand access to healthier options through farm-to-school lunch programs and other strategies.)
The Minnesota Beverage Association responded to public pressure with a campaign to reduce high-calorie options from school vending machines. A 2008-2009 report from the trade group stated that the association had removed full-calorie soft drinks from all schools and reduced calories in school vending machine beverages by 85 percent.
The Penn St. researchers offered several theories for their results -- including the fact that eating patterns are set more by meals at home than by vending machine offerings at school. The researchers noted that middle-schoolers have such structured, busy schedules that they might not have time to pause for an unhealthy treat. According to Van Hook:
“Schools only represent a small portion of children’s food environment. They can get food at home, they can get food in their neighborhoods, and they can go across the street from the school to buy food. Additionally, kids are actually very busy at school. When they’re not in class, they have to get from one class to another and they have certain fixed times when they can eat. So, there really isn’t a lot of opportunity for children to eat while they’re in school, or at least eat endlessly, compared to when they’re at home. As a result, whether or not junk food is available to them at school may not have much bearing on how much junk food they eat.”
The researchers also noted that the results are specific to middle school students. It's possible that junk food restrictions at pre-schools and elementary schools might be more meaningful, because food tastes and habits are set at earlier ages.