Evidence From a Natural Experiment
ResearchPosted on rand.org Mar 11, 2021Published in: Journal of Adolescent Health, Volume 67, Issue 6, pages 804–813 (December 2020). doi: 10.1016/j.jadohealth.2020.03.004
Existing evidence on relationships between school food environments and children's in-school purchases, dietary behaviors, and body composition is based on observational studies that are vulnerable to residential selection bias.
This study leveraged exogenous variation in school environments generated by the natural experiment due to military parents' assignment to installations. We analyzed 1,010 child-wave observations from the Military Teenagers Environments, Exercise, and Nutrition Study collected during 2013–2015. Using multiple linear and logistic regression, we examined whether the number of competitive food and beverage (CF&B) items available for purchase in school, overall and by type (unhealthy, healthy, neutral), was associated with in-school food purchases, dietary behaviors, and body mass index (BMI) outcomes. Covariates included child and family characteristics and the healthiness of the home food environment.
Unhealthy item availability was positively associated with purchasing any sweets (adjusted odds ratio [AOR], 1.30; p < .01), snacks (AOR, 1.23; p < .01), and sugar-sweetened beverages (AOR, 1.19; p = .01). However, there were no significant associations with overall food and beverage intake (e.g., sweets, soda) nor BMI outcomes. The home food environment was significantly associated with all outcomes.
Access to unhealthy CF&B items may influence in-school purchases but does not appear to influence overall dietary behaviors and BMI outcomes. Substitution of caloric intake across locations within versus outside of school may play a role in explaining why purchases were associated with unhealthy CF&B availability but overall diet and downstream BMI were not.
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