01/18/2012 12:12 pm ET

School Vending Machines, Weight Gain Link Disputed By New Study

The explosion of obesity and unhealthy eating among children in recent years is deadly serious. It's already increased the prevalence of things like diabetes and hypertension in those under 18 -- and it bodes very ill for the long-term health of a generation. It's one thing for a person to gradually gain weight over the course of his or her life, becoming portly by middle age. It's quite another to already be obese by the time you're in high school.

That's why, over the past several decades, public health experts have been tearing out their hair looking for solutions to childhood obesity. Because almost every child attends school, that environment has naturally become target number one in the fight. Many school districts have made inroads overhauling school lunch and breakfast menus to be emphasize healthy meals -- but that's a major commitment, and not always a popular move. The difficulty of addressing central nutrition has led many educational advocates -- including President Obama himself -- to shift their focus to vending machines in schools. They're easy targets: not many people are going to disagree with the idea that it's probably not smart to sell Fritos and Sprite in middle schools while you're trying to fight childhood obesity.

But a new study from two researchers at Penn State, published this month in Sociology of Education, argues that school vending machines don't actually lead to weight gain among adolescents.

The study's authors, Jennifer Van Hook and Claire E. Altman, have said that they had expected to find a link between the presence of vending machines and weight gain, both because vending machines advertise unhealthy foods and because they allow students to eat unhealthy snacks throughout the school day. But after a systematic review of health data on thousands of middle school students from across the country, they found that students at schools with access to "competitive foods" -- those sold above and beyond normal meals, as in vending machines and snack bars -- gained no more weight than those at schools without competitive foods.

Van Hook and Altman checked their findings by looking at students who were in different schools for different lengths of time -- say, students who stayed in elementary school through sixth grade and those went to middle school in sixth grade. This led, in some cases, to students who had one fewer year than others in an environment with vending machines. If vending machines lead to weight gain, such students would gain less weight than their peers -- but the study found no such correlation.

Indeed, there was no population for whom vending machines led to any serious difference in weight outcomes: not girls or boys, not Hispanics or Asians, not students from rich families or poor families.

Van Hook and Altman suggest two central explanations for their findings. They suggest that the structured environment of middle schools makes it hard for students to buy very much food throughout the day; it's hard to find enough time while ducking out of Algebra to wolf down a whole bag of M&Ms.

That leaves advertising as the most potentially powerful agent of change. And the researchers speculate that, for the most part, adolescents have already developed their dietary habits by the time they get to middle school. The presence of a Coca-Cola logo on campus isn't going to change minds that have already established preferences.

Indeed, the study suggests, tantalizingly, that there's very little that can be done to influence weight outcomes by the time a child reaches middle school. "We found strong associations between children's eight-grade weight and factors like family SES [social economic status], indicators of school SES, race/ethnicity, maternal employment, and parental nativity," it reads. "However none of these factors explain weight gain among young adolescents. Overall, the results suggest that weight during early adolescence [...] is strongly shaped by how heavy children were when they were young."

It's hard to think of many benefits inherent in installing vending machines in schools (aside from revenue, which is not inconsequential). So we might decide that they're worth removing, just on the principle that our schools should encourage healthy lifestyles whenever possible. But by the same token, this study helps prove that removing vending machines isn't going to do much to change childhood health across the country.