One of the policy responses to the growing trend in childhood obesity has been to try to reduce children’s opportunities to purchase competitive foods in schools or improve the nutritional quality of foods sold. Yet it has remained unclear what impact, if any, these efforts are likely to have on children’s weight. The research presented here uses longitudinal data to assess the association of the introduction of and exposure to competitive foods with weight gain among children in middle school. The results suggest that the sale of competitive foods in school is unassociated with weight gain among middle-school children. The estimated effect was small and statistically insignificant regardless of how we measured competitive food sales or weight status or which statistical modeling technique we used. Moreover, this basic conclusion did not vary by children’s gender, race/ethnicity, or family SES.
This finding should be interpreted within the context of the study’s limitations. First, although we go beyond other research by following children’s weight and exposure to school environments over time for a nationally-representative sample, our study is observational and therefore does not provide true causal estimates such as can be obtained from random-controlled experimental designs. Second, our results do not preclude the possibility that specific school food policies are associated with weight gain among children, such as aggressive advertising efforts or school activities and schedules that actively encourage children to purchase soda, juice, or candy from vending machines. Furthermore, we do not explore variations in this effect with respect to the amount and cost of food and drinks being sold and consumed in schools. In recent years, school districts have restricted the types of foods and beverages sold in vending machines and snack bars, so it would be interesting to assess whether these policy changes have altered food consumption patterns and reduced the risk of obesity among students, as suggested would be the case by a recent study (Schwartz, Novak, and Fiore 2009
). Third, it is important that our findings not be generalized to older children. The effects may be greater for high school students (as found by Anderson and Butcher, 2006
) because older adolescents have less rigid school schedules and more freedom and money to purchase competitive foods than the middle school children in our study. Finally, it is important to understand that we estimate average population–level effects. It remains possible that some individual children may gain weight when given opportunities to purchase competitive foods because they tend to select higher-calorie foods or purchase a lot of food.
Despite these limitations, our study of the average effects of competitive food sales lends support to a growing body of evidence (Datar and Nicosia 2009
; von Hippel et al. 2007
; Fletcher, Frisvold and Tefft 2010
) that competitive food sales in elementary and middle schools should not be blamed for the growing obesity epidemic or disparities in childhood obesity at the population level. This conclusion seems inconsistent with the external
perspective on children’s susceptibility to food cues in school environments. Given the limitations of our study and the strength of prior research, we do not take issue with the basic conclusion about the unhealthy effects of consuming high-calorie food and beverages of low nutritional value, or with the idea that easy access to food increases intake. However, we do suggest that cross-sectional studies may be flawed because they do not account for how heavy children were before they attended schools that sell competitive foods. As suggested by the developmental perspective, children’s dietary patterns, food preferences, and therefore their weight trajectories, may be firmly established by the time they reach middle school. Additionally, as suggested by von Hippel and his colleagues (2007)
, children may face greater risks for obesity at home than at school, even if their school sells competitive foods. Schools are highly structured, hierarchical, and effective at organizing students’ time, and structure like this may reduce the time children spend snacking. More research is necessary to assess this idea.
To the extent that the findings reported here are robust to their limitations, they may prove disappointing for those seeking to design school-based interventions to improve children’s health. Schools seem to be natural places in which to enact cost-effective interventions. Because students are captive audiences, schools can communicate and interact with millions of children for extended periods of time. Schools also have the institutional capacity to coordinate and deliver consistent and well-defined interventions through an army of teachers and administrators. Yet, schools may not be good at addressing the root causes of childhood obesity that originate in children’s homes and communities. Not only do we find that competitive food sales within schools are, on average, unrelated to obesity, but other research suggests that school-based interventions to reduce childhood obesity are often unsuccessful (Sharma 2006
; Kropski et al. 2008
). Overall, schools may help promote better eating and provide opportunities for physical activity, but they do not seem to be effective at changing a student’s weight. The challenge is to develop interventions that reach into the home and community. Perhaps those interventions can start with schools, but they probably need to reach beyond them to be effective.