Supermarket access, transport mode and BMI: the potential for urban design and planning policy across socio-economic areas

Objective: To investigate dietary intake, BMI and supermarket access at varying geographic scales and transport modes across areas of socio-economic disadvantage, and to evaluate the implementation of an urban planning policy that provides guidance on spatial access to supermarkets. Design: Cross-sectional study used generalised estimating equations to investigate associations between supermarket density and proximity, vegetable and fruit intake and BMI at five geographic scales representing distances people travel to purchase food by varying transport modes. A stratified analysis by area-level disadvantage was conducted to detect optimal distances to supermarkets across socio-economic areas. Spatial distribution of supermarket and transport access was analysed using a geographic information system. Setting: Melbourne, Australia. Subjects: Adults (n 3128) from twelve local government areas (LGA) across Melbourne. Results: Supermarket access was protective of BMI for participants in high disadvantaged areas within 800m (P=0.040) and 1000m (P=0.032) road network buffers around the household but not for participants in less disadvantaged areas. In urban growth area LGA, only 26% of dwellings were within 1 km of a supermarket, far less than 80-90% of dwellings suggested in the local urban planning policy. Low public transport access compounded disadvantage. Conclusions: Rapid urbanisation is a global health challenge linked to increases in dietary risk factors and BMI. Our findings highlight the importance of identifying the most appropriate geographic scale to inform urban planning policy for optimal health outcomes across socio-economic strata. Urban planning policy implementation in disadvantaged areas within cities has potential for reducing health inequities.