Neighbourhood food environments and body mass index among New York City adults.

BACKGROUND
Studies evaluating the impact of the neighbourhood food environment on obesity have summarised the density or proximity of individual food outlets. Though informative, there is a need to consider the role of the entire food environment; however, few measures of whole system attributes have been developed. New variables measuring the food environment were derived and used to study the association with body mass index (BMI).

METHODS
Individual data on BMI and sociodemographic characteristics were collected from 48 482 respondents of the 2002-2006 community health survey in New York City and linked to residential zip code-level characteristics. The food environment of each zip code was described in terms of the diversity of outlets (number of types of outlets present in a zip code), the density of outlets (outlets/km²) and the proportion of outlets classified as BMI-unhealthy (eg, fast food, bodegas).

RESULTS
Results of the cross-sectional, multilevel analyses revealed an inverse association between BMI and food outlet density (-0.32 BMI units across the IQR, 95% CI -0.45 to -0.20), a positive association between BMI and the proportion of BMI-unhealthy food outlets (0.26 BMI units per IQR, 95% CI 0.09 to 0.43) and no association with outlet diversity. The association between BMI and the proportion of BMI-unhealthy food outlets was stronger in lower (<median for % poverty) poverty zip codes than in high-poverty zip codes.

CONCLUSIONS
These results support a more nuanced assessment of the impact of the food environment and its association with obesity.