Obesity among black women in food deserts: An "omnibus" test of differential risk.

The "omnibus" hypothesis, as forwarded by Ford and Dzewaltowski (2008), asserts that poor-quality food environments differentially affect low- and high-socioeconomic status (SES) populations. Accordingly, we examine, in a large sample of non-Hispanic (NH) black women, whether low access to healthy food corresponds with increased risk of obesity among residents of low- and high-poverty neighborhoods. In addition, we analyze whether any discovered association between low-food access and obesity appears stronger in neighborhoods with a high proportion of black residents. We retrieved body mass index (BMI) data for 97,366 NH black women residing in 6258 neighborhoods from the California Department of Public Health birth files for years 2007-2010. We linked BMI data with census tract-level data on neighborhood food access from the 2010 Food Access Research Atlas and neighborhood poverty and black composition from the 2006-2010 American Community Survey 5-year estimates. We applied generalized estimating equation methods that permit analysis of clustered data within neighborhoods. Methods also controlled for individual-level characteristics which might confound the relation between food access and obesity, including health insurance status, age, education, and parity. Results indicate that low-food access does not impact risk of obesity among NH black women residing in low-poverty neighborhoods. However, low-food access varies positively with risk of obesity in high-poverty neighborhoods. Moreover, the association between low-food access and obesity appears stronger in high-poverty, high-black composition neighborhoods, relative to high-poverty, low-black composition neighborhoods. Our findings support the omnibus hypothesis and indicate a potential interaction between factors in the local food and social environments on an individual's risk of obesity.