School Junk Food Ban Study Loaded With Empty Calories

A study showing that California high school students consume fewer calories on campus than teenagers in other states following a state ban on junk food sales has been greeted with a small burst of excitement. But there is no evidence that the ban actually influenced teen eating habits.

First the good news: Unlike the subjects in some previous studies, these kids are not snorting Doritos at home and making up the difference. They are generally eating fewer calories per day than students in states that don't ban junk food at school. Nanny state nutritionists are salivating over the findings. 

The study, by the University of Illinois, involved 680 students in 15 states — 114 in California — during a four-month period in 2010. The students reported their eating habits, and researchers compared California high school students' intake with those in other states. They determined California teens were consuming about 160 fewer calories per day than students in other states, and the decrease was taking place at school. The California teens consumed less fat, sugar, and salt at school, but they also consumed fewer vitamins and minerals. The teens just ate less of everything at school in California, getting only 21 percent of their daily calories while at school compared to 28 percent for teens in other states. California teens made up some of the difference elsewhere, but when all the numbers were crunched, they were still eating less overall.

But the study leaves plenty of unanswered questions. First, we have no idea what the California teens' eating habits were prior to the junk food ban (passed in 2007). We don't know if California students are eating less than they used to, which you'd think would be important data if you're calculating the success of a school junk food ban. (There is a brief reference to another study relevant to the matter, with the results vaguely described as "cautiously optimistic")

Second, more than half the students on the non-California side of the study attended school in Southern states. This is relevant, because while California's teen obesity rate is high, it is not as high as the obesity rate in the South. Again, because the study only measures intake post-ban, for all we know the California students had already been consuming fewer calories than their peers in this study.

Finally, researchers note that even allowing for the cutting out of fat and sugar, students' food consumption at school wasn't really healthier, per se. "The nutritional composition of California students' in-school diet was similar," the study states.  (The study seems to assume here that more nutritional choices aren't being offered, rather than that students are declining to eat them.) In the comments section, the researchers offer all sorts of caveats about the inbalance in representation of the subjects, the problems of asking teens to accurately report their own eating habits, and the possibility of self-selection bias.

The study's authors concede that they cannot conclude California's laws were the cause of any differences in intake. That uncertainty doesn't stop them from proposing even more policy changes.

But the students in California feel like they're eating healthier, and isn't that what matters? Here's what an Elk Grove High School Student told San Francisco's ABC affiliate: "This would be a large size, these shorts, this shirt. I do feel like I would be heavier." He feels like he would weigh more if junk food hadn't been banned.

California Assemblyman Richard Pan, D-Sacramento, a pediatrician, weighs in: "We've just shown that in the school, we've created an environment where kids will take fewer calories. We can now use this as information to talk to parents about, 'How do we create the environment at home?'"

Elsewhere: Reuters argues that our mocking of fat people is discouraging them from losing weight, so knock it off. Also, it's all the fault of advertisements and restaurants.