Compliance with nutrition standards in Mexican schools and their effectiveness: a repeated cross-sectional study

BACKGROUND: Mexico approved mandatory nutrient-based standards for foods sold in schools in 2011. The aim of this study was to analyse the association between compliance with nutrition standards for foods sold in schools and children’s school snacks. METHODS: Data came from three surveys representative of Mexican elementary schools in 13 states and their students (2012, 2013 and 2015); n = 645 children from N = 99 different schools. Information on foods sold in schools and snacks consumed by children was collected through direct observation. Compliance with the standards was defined as the proportion of foods sold in school which met nutrition criteria established by the standards. Snacks were classified as healthy if they contained at least one fruit or vegetable and had no sugar-sweetened beverages. Robust logistic regression models for cross-sectional and repeated surveys aggregated at the school-level were fitted to quantify the association between school compliance with standards and healthy snacks. RESULTS: On average across waves 27% of foods sold complied with nutrition standards; 18% of children consumed a healthy snack. For snacks purchased in school, a 10% increase in school compliance with the standards was associated with a 32% increase in the odds of a healthy snack (OR = 1.32; 95%CI 1.09,1.61); no association was observed for snacks brought from home. The odds of a healthy snack increased over time in schools where compliance with the standards improved (OR = 3.89; 95%CI 1.47,10.31) but not in those where compliance remained constant or decreased. CONCLUSIONS: Only a small proportion of children are eating healthy snacks in school. School compliance with standards increases the likelihood of a healthy snack if it is bought at school. Our findings support better implementation of the standards and additional strategies to enhance the policy to achieve its aim of reducing childhood obesity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12889-018-6330-8) contains supplementary material, which is available to authorized users.