Impact of the external school food environment on the associations of internal school food environment with high schoolers' diet and BMI

Objective: To examine associations of school food availability with student intake frequency and BMI, and whether the number of neighbourhood food outlets modifies these associations. Design: Baseline assessment of a nationally representative cohort study of US 10th graders. Students reported intake frequency of fruits and vegetables (FV), snacks and soda. BMI was calculated from measured height and weight. Administrators of seventy-two high schools reported the frequency of school availability of FV, snacks and soda. The number of food outlets within 1 km and 5 km were linked with geocoded school addresses. Data were analysed using adjusted linear and logistic mixed models with multiple imputation for missing data. Setting: US 2009-2010. Participants: Totally, 2263 US 10th graders from the Next Generation Health Study (NEXT). Results: Greater school FV availability was positively associated with student FV intake. Food outlets within 5 km of schools (but not 1 km) attenuated the association of school FV availability with student intake; this was no longer significant at schools with > 58 food outlets within 5 km. School food availability was not associated with student BMI or student snack or soda intake. Conclusions: School food availability was associated with student intake of FV, but not with snacks, soda or BMI. Attenuation of the observed associations by the school neighbourhood food environment indicates a need to find ways to support healthy student eating behaviours in neighbourhoods with higher food outlet density.