Mapping the Cost of a Balanced Diet, as a Function of Travel Time and Food Price

We present a new method for analyzing spatial variation in the cost of a balanced diet, as an alternative to food desert classification. Our specific hypothesis is that the cost of a balanced diet varies according to where one lives, as a function of travel and food item costs. We collected price data for the USDA Thrifty Food Plan from approximately 30 percent of food retail outlets of various kinds in the three Gulf Coast counties of Mississippi, and these prices were extrapolated to the remaining stores. Transportation costs were calculated for both driving by automobile and the combination of walking and public transportation by bus, accounting for both the shoppers' time and the cost of automobile mileage. We developed a "traveling purchaser problem" algorithm to estimate the lowest-cost combination of travel and food costs for purchasing all items in the Thrifty Food Plan for each residential parcel in the study area, and mapped the resulting costs and examined their variation. Estimated costs varied more because of transportation costs than food prices, and ranged from US$109 to US$215 for automobile travel and from US$111 to US$439 for a combination of walking and public transportation. In general, costs were lowest in the more populated areas near the coast and higher in more rural areas further inland. Results of this analysis demonstrate that the cost of acquiring a balanced diet varies considerably and more or less continuously. Food is not equally cheap for all; it depends on where one lives. For any given location, an estimate of the cost of a balanced diet, including both food price and transportation, is more useful than a classification as food desert or not in understanding access issues and needs. Furthermore, policy alternatives that are intended to influence access should be evaluated based on how much they influence costs, and for whom, depending on where people live.