In a study of young girls residing in California, living in close proximity to convenience stores, and to a lesser extent, drug stores, was positively related to overweight or obesity and BMI z-score after 3 years of follow-up. The availability of produce vendors/farmer’s markets was associated with a lower risk of overweight or obesity over time. These associations are consistent with previous studies conducted among adolescents and adults residing in Midwestern and southern states6,9,20
, and suggest that relationships may apply to girls before adolescence.
The observed associations with BMI z-score may be mediated by unhealthy dietary behaviors. Past studies among young children have found that living within close proximity to convenience stores was associated with higher consumption of potato chips, chocolate and white bread49
, and lower consumption of fruits50
. Conversely, there were no significant associations between the availability of fast-food restaurants, supermarkets, or other food stores within a 0.25-mile network buffer and girls’ overweight or BMI z-scores.
A comparison of neighborhood food store availability within two neighborhood boundaries demonstrates the importance of walkability. When the boundary was expanded to a 1.0-mile network buffer, previous associations were attenuated; however, a protective association was observed between the availability of produce vendors/farmer’s markets and risk of overweight or obesity. Given that a 1.0-mile network buffer may be too large for children to navigate, it is likely the parents/caregivers who are purchasing fresh produce for their households. The dose–response relationship between produce vendors/farmer’s markets and the reduced risk of overweight or obesity also bears important implications. Increasing the accessibility of fruits and vegetables to parents/caregivers may improve the diets of young children, and help to protect against the development of overweight or obesity over time.
A key strength of the study is the longitudinal nature of the data. Because repeated measurements of height and weight were collected from the study participants, it was possible to examine how neighborhood food stores affect weight change over time. Modeling both outcomes of overweight status and BMI z-score allows for the estimation of the relative risk of overweight or obesity as well as the magnitude of change in BMI z-score over 3 years.
This study is limited by a relatively small sample size. For example, “Asian/Mixed/Other” was combined into one race/ethnicity category because only 7.7% of girls identified as Asian and 9.9% of girls identified as mixed or other race/ethnicity. This may have resulted in residual confounding by race/ethnicity. Excluding girls who changed residences after the first year of follow-up may have further limited the ability to determine how changes in the neighborhood food environment affect changes in girls’ weights over time. Previous research has suggested that the effects of the neighborhood environment on children’s health outcomes are small. However, the literature describing the neighborhood food environment in relation to children’s weight is still growing, and these findings corroborate previous studies that have also observed similar associations with neighborhood food stores and BMI.51,52
Second, there is potential for misclassification of the neighborhood food environment. Because neighborhood assessments were conducted at baseline, this study assumes the food environment has not changed during follow-up. However, most food establishments are relatively stable and it is unlikely that substantial changes to the neighborhood occurred within a few years. Individual food store types were also examined independently of other food stores in analytic models. There may be multiplicative effects in neighborhood food stores on girls’ BMI z-scores over time. Future studies might consider utilizing indices that capture the diversity of the neighborhood food environment, or examine potential effect modification by other food stores on these associations.53-55
In addition, information was not collected on where the girls’ parents shopped for food, or the food items sold in various stores. Although it was hypothesized that produce stores/farmer’s markets, small grocery stores, specialty stores and supermarkets sold mostly healthy food items, and that convenience stores, fast-food restaurants, and full-service restaurants, sold mostly unhealthy food items, the validity of these hypotheses are dependent on the availability of foods within individual stores. Thus, not all supermarket foods fit within the healthy food groups of fruits, vegetables, and whole grains, and similarly, not all foods served in fast-food or full-service restaurants might contribute to obesity, or necessarily be high in saturated fat, sodium, and added sugars.54,56-59
It remains unknown how the stores nearest girls’ homes actually influenced their dietary consumption.
Parental beliefs and neighborhood income may act as unmeasured confounders. Parents residing in higher-income neighborhoods may have easier access to large supermarkets and farmer’s markets, and limited access to convenience stores or fast-food restaurants. In addition, these parents are generally more health-conscious and more likely to promote healthy eating and physical activity among their children. While it was possible to statistically adjust for parent’s/caregiver’s education level and household income, residual confounding may still exist. The dichotomy of household income at $100,000 helped to ensure an equal number of study participants above and below the cut-off; however, a household income <$100,000 does not translate into low-income. Future studies should collect more detailed information on parental beliefs and behaviors, in a more income-diverse population to better handle confounding. This study also did not correct for multiple comparisons of neighborhood food store types, and should be considered exploratory.