Earlier research indicates that the types of food stores and food availability in neighborhoods are associated with neighborhood characteristics (Morland, Wing et al. 2002
; Zenk, Schulz et al. 2005
; Block and Kouba 2006
; Moore and Diez Roux 2006
; Powell, Slater et al. 2007
), dietary intake (Morland, Wing et al. 2002
; Franco, Diez-Roux et al. 2009
), and obesity (Green, Hoppa et al. 2003
; Larson, Story et al. 2008
; Li, Harmer et al. 2008
; Morland and Evenson 2008
). Few studies have examined these associations stratified by neighborhood race and SES.
Contrary to the study hypothesis, greater healthy food availability was associated with higher BMI among individuals living in predominately white neighborhoods after adjustment for demographic variables and dietary intake. One explanation for this unexpected finding is that individuals living in neighborhoods with low healthy food availability choose to travel outside their neighborhood to obtain healthy food. Indeed, individuals residing in neighborhoods with low healthy food availability reported more often using a car as the main mode of transportation (83%) and reported virtually no walking (1%) compared to individuals in this subgroup residing in medium and high healthy food availability neighborhoods (55%, 60% for car use and 7%, 8% for walking, respectively; p<0.001). Furthermore, individuals in low healthy food availability neighborhoods had better dietary intake (mean HEI=50) compared to their counterparts residing in medium and high healthy food availability areas (mean HEI=47, HEI=48 respectively; p<0.001). Thus, in this urban, predominately white population, higher neighborhood healthy food availability was not a marker for either healthier dietary intake or body weight.
Few studies have empirically assessed healthy food availability and the association with health outcomes. A cross-sectional study in 12 suburban/urban communities measured the availability of low-fat and high-fiber products and found positive, significant correlations between neighborhood availability of these products and self-reported healthfulness of individual diet (Cheadle, Psaty et al. 1991
). In another cross-sectional study, lower healthy food availability, measured by the NEMS-S, was significantly associated with poorer dietary patterns (fat and processed meats pattern) in urban and suburban Baltimore (Franco, Diez-Roux et al. 2009
). The association became insignificant when adjusted for race; higher neighborhood healthy food availability was not significantly associated with better dietary patterns (whole grains and fruit pattern). The authors noted that healthy food availability might be a proxy for neighborhood racial composition, given the strong correlation that was documented between the two factors (Franco, Diez Roux et al. 2008
). Thus, the association between healthy food availability and diet quality would be masked after controlling for race. With the exception of individuals in predominately white HANDLS neighborhoods, unadjusted results were insignificant for BMI. This suggests that neighborhood healthy food availability, as assessed in the current study, may not be an accurate measure to capture food consumption patterns in this population. Information on the use of restaurants and the location of where participants most frequently shop for food may begin to clarify the influence the neighborhood food environment has on health.
There may be several explanations for the lack of significant results among individuals living in predominately black or low-SES neighborhoods. Recent literature has documented important implications and considerations for measuring food availability in minority and low-income neighborhoods (Gittelsohn and Sharma 2009
; Odoms-Young, Zenk et al. 2009
). Social constructs likely play an important role for understanding neighborhood disorder and safety concerns that may impede the use of local food stores, regardless of availability (Odoms-Young, Zenk et al. 2009
). Thus, the availability of healthy foods would have little impact on health outcomes in low-income, minority neighborhoods. In predominately black and low-SES HANDLS neighborhoods, individuals residing in medium or high healthy food availability neighborhoods more often reported seeing serious crime as a common occurrence compared to their counterparts residing in low healthy food availability neighborhoods (p<0.001, data not shown). Second, immigrant groups, particularly Asian Americans in Baltimore City, have operated businesses in low-income, black neighborhoods for a number of years (Gittelsohn and Sharma 2009
; Odoms-Young, Zenk et al. 2009
). There may be language and cultural barriers and feelings of discrimination by local food store owners that reduce the use these neighborhood establishments. Third, consumer interests need consideration when assessing the effects of neighborhood food availability. Although foods of cultural preference would be expected to be available in a neighborhood, these foods may be inadequately captured on standard surveys (e.g., NEM-S). Thus, if measures of the food availability do not capture food relevant for the population, the power to detect neighborhood effects is reduced. Finally, consumers residing in low-income, minority neighborhoods, may often have concerns that food quality, fresh or otherwise, is poor and choose to purchase foods outside their neighborhood (Gittelsohn and Sharma 2009
This study has several strengths. First, BMI was objectively measured; this method, rather than self-report, are preferred for large epidemiologic studies. Second, a systematic assessment of food stores was conducted in Baltimore City. Since national business data may inaccurately classify food stores (Cates S. 2000
), this method was a significant improvement from previous studies. Finally, the stratified sampling design allowed for associations to be compared by neighborhood characteristics.
Nevertheless, this study has some limitations. First, the study was cross-sectional which limited the ability to make causal statements about observed associations. Second, census tract boundaries were used to approximate neighborhoods, which created the potential for measurement error when determining neighborhood food availability. If measurement error were present, it would be expected to be non-differential; thus, results would be biased towards the null. Third, no information was available on where participants shopped. It was assumed that the neighborhood environment was most influential on food procurement behaviors. Fourth, food store data was collected in 2006–2007 while individual baseline data was collected from 2004–2008. The current analysis assumes that neighborhood characteristics and individual behaviors and health outcomes were relatively stable during this time period. The time-point in this study represents the mid-point of the baseline data collection years, which minimizes the magnitude of this potential bias. Finally, healthy food availability scores were imputed based on a previous study implemented in Baltimore. Given that the characterization of food stores was completed using the same procedures and in the same geographic location as the current study, it is assumed that these imputed values are solid estimates of the true HFAI. Furthermore, a prior study suggests that healthy food availability may be a proxy for neighborhood racial composition (Franco, Diez Roux et al. 2008
); stratification by neighborhood characteristics was a strategy used to circumvent this issue and attempt to observe the independent effect of healthy food availability.
Neighborhood food availability is only one part of the built environment that may facilitate or provide the opportunity for individuals to make healthier choices and ultimately reduce BMI. Taken together with previous work, it is likely that the influence of the food environment operates differently across neighborhoods of varying characteristics. The mechanisms for these associations deserve future investigation since neighborhood food availability may partially account for racial and SES disparities in obesity and dietary intake. The potentially large public health impact that could be gained from further investigation warrants continued exploration.