Objective Individual-level determinants of diets are well known. Recently, physical proximity to neighborhood supermarkets has been proposed as an environmental determinant of access to healthy foods, diets and health. The present study hypothesized that supermarket choice, conceptualized as the proxy for underlying personal factors, would better predict supermarket accessibility and diet quality than mere physical proximity. Methods The Seattle Obesity Study geocoded respondents’ home addresses and locations of their primary supermarkets. Primary supermarkets were stratified into low-, medium- and high- cost according to the market basket cost of 100 foods. Data on fruit and vegetable consumption were obtained through telephone surveys. Linear regressions examined associations between physical proximity to primary supermarkets, supermarket choice, and fruit and vegetable consumption. Descriptive analyses examined whether supermarket choice outweighed physical proximity among lower-income and vulnerable groups. Results Only one-third of respondents shopped at their nearest supermarket for their primary food supply. Those who shopped at low-cost supermarkets were more likely to travel beyond their nearest supermarket. Fruit and vegetable consumption was not associated with physical distance but, with supermarket choice, after adjusting for covariates. Conclusions Mere physical distance may not be the most salient variable to reflect access to supermarkets, particularly among those who shop by car. Studies on food environments need to focus beyond neighborhood geographic boundaries to capture actual food shopping behaviors.

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Objectives This study introduced new concepts and measures to identify food deserts. Methods Physical and economic access to supermarkets were estimated for five low-income groups in Seattle-King County. Physical access was measured using GIS to delineate service areas around each supermarket based on a 10-minute travel duration by four modes: walking, bicycling, riding transit, or driving. Economic access was assessed by stratifying supermarkets into low-, medium-, and high-cost types. Combining income and access criteria generated multiple ways to estimate food deserts. Results The five low-income group definitions yielded total vulnerable populations ranging from 4 to 33% of the County’s population. Almost all of the vulnerable populations lived within a 10-minute drive or bus ride of a low- or medium-cost supermarket. Yet a high of only 34% of the vulnerable populations had the option of walking to any supermarket, and a low of 3% did so to a low-cost supermarket. Conclusions The criteria used to define low-income status and access to supermarkets greatly affect estimates of populations living in food deserts. Measures of access to food must include travel duration and mode, and supermarket food costs.