The data from this study describe three important patterns of in-store food availability in the USA. First, there were large variations among different store types and much smaller variations within individual store types in the absolute and relative shelf length of healthy and unhealthy food items. Second, while convenience stores, liquor stores, and small food stores offer the least healthy mix of items, stores of all types devote more shelf space to unhealthy than to healthy items. And third, it appears that the “food environment” may be different in different regions in the USA, with stores in Louisiana offering a less healthy mix of foods than stores in Los Angeles. The measurements and ratios obtained in this study can be used for further research into the impact of the food environment on consumption and to develop simple criteria for the “healthfulness” of stores.
Several other research groups have assessed the availability of various foods in different types of food stores.22–27
In these studies, nearly all supermarkets contain some fresh fruits and vegetables, 24,26,27
but only approximately one fourth to one third of small stores or convenience stores contained any fresh fruits or vegetables.25,27
Block et al. in suburban Chicago and Connell et al. in the lower Mississippi delta enumerated the items that were available from a standard “market basket” and found that supermarkets contained nearly 100% of the fresh fruits and vegetables, but small independent groceries contained 29–45% and convenience stores contained only 8–28% of these items.24,28
In contrast, both Block and Connell found that supermarkets contained nearly 100%, independent smaller groceries contained 60–71%, and convenience stores contained 48–68% of the fats, oils, sugars, and sweets in their market baskets—indicating that customers have more extensive choices in calorie-dense items than fruits and vegetables in smaller stores.24,28
To our knowledge, this is the first study that has measured the length of shelf space allotted to these items in the USA. In addition, very few studies have considered liquor stores and drug stores as sources of food, even though these stores may be important sources of food for families that do not own cars or live in neighborhoods that are distant from supermarkets. We found that these stores are very similar to convenience stores in the small amount of shelf space used for healthy foods and overabundance of unhealthy foods.
Studies of food availability are hampered by variation between studies on how food stores are defined. In this study, we categorized stores not based on Standard Industry Classification (SIC) or North American Industry Classification System (NAICS) codes but rather based on their size, number of cash registers, primary products, and whether they were independent or part of a chain. SIC and NAICS codes are widely available but do not differentiate between supermarkets, medium-sized food stores, and small food stores, which differ markedly in their mix of foods sold. Our classification is more consistent with the functions these stores serve to their customers, but cannot be readily determined from widely available datasets. To advance this research, it would be helpful to develop a better classification system for food stores and include this in large datasets.
Limitations of this study include the fact that the only stores observed were those that sold alcohol. Based on subsequent store observations in Louisiana, we estimate that approximately 85% of food stores, 75% of convenience stores, and 40% of drug stores sell some type of alcoholic beverages. Differences in food availability in those stores that do and do not sell alcohol in these subsequent observations did not seem large, but more data are needed on this. Thus there is a potential bias in an unknown direction introduced into our study by limiting the store observations to those that sell alcohol. In addition, our store measurements did not collect information about other in-store factors that might influence sales, such as the height of shelves, number of shelves, or whether the items were displayed on the sides or ends of aisles. While this simplification approximates a measure of likelihood that a random shopper would “bump into” an item type, it is an incomplete measure of the prominence of the item type. Food stores are extremely complex environments to measure, and even if every item could be measured, experts would have difficulty agreeing on which items should be classified as “healthy” or “unhealthy”. To avoid being overwhelmed with this complexity, we chose to restrict our measurements to a very limited number of items for which there would be a general consensus regarding their value to health. Our study also was conducted only in two geographic areas, and we do not know the degree to which the stores in these areas are representative of those in the rest of the country. In spite of these limitations, this study provides new and useful information about the environment that customers encounter inside stores.
Our findings have implications for both researchers and policymakers. Researchers conducting studies on the relationship between the food environment and diet or health can often obtain databases that characterize food stores by type, but they rarely have information about the foods available in those stores. Our measurements indicate that store type is a reasonable proxy measure for store contents. At the same time, they also indicate that a full measurement of the food environment must take into account all of these store types, including liquor stores and drug stores, rather than only stores that present themselves as primarily selling food. If these other sources are missed, the studies will underestimate the abundance of unhealthy food available in many communities.
Policymakers seeking to improve health through dietary change or to reverse the obesity epidemic have an interest in increasing access to fruits and vegetables. While this may be translated into a desire to increase the number of food stores in low-income neighborhoods, a policy to accomplish this could have unintended adverse effects if it further increases the overabundance of unhealthy snack foods. Focusing only on increasing the number of supermarkets could have this effect because supermarkets offer more shelf space for unhealthy than healthy items. A better policy approach may be to increase the number of food stores of any size that meet criteria for the healthfulness of their mix of items. Our measurements suggest that a simple ratio of the shelf length of healthy items to the shelf length of unhealthy items easily summarizes store contents and distinguishes store types. The ratio used in this study should be refined to take into account other important items (particularly non-carbonated sweetened beverages), but a very similar ratio could easily be developed and used in policymaking.