In this study of Atlantans, the lowest average distance traveled to a food establishment was greater than 4.5 miles. This is a much longer distance than the 1-km to 1-mile buffers around homes that are often constructed in studies of physical activity environments [23
]. Therefore we have to be cautious about interpreting the relationship between obesity if it is assumed that an individual’s food environment is constituted only or mostly within these buffers.
Although many food trips are currently outside of the residential neighborhood, a 1-km buffer is still a good indicator of food access that may be related to shorter journeys, more walking for transportation and greater support of local food sources. Participants travelled furthest to larger superstores for food, as might be expected based on variety and cost considerations. The implications for greenhouse gas emissions and air pollution for longer trips to superstores should be evaluated relative to potential efficiencies if fewer trips to obtain food overall are made. Travel for food or food miles
is becoming a central focus of strategies to reduce greenhouse gas emissions [36
Food trips were longer when people started from a non-home location or lived in suburban type location without connected streets, mixed land uses or high residential density. Non-white, those without a degree, and lower-income subgroups travelled longer distances for food, suggesting local food sources may be unavailable and travel to food may be an additional hardship for the underserved. Increased time spent in cars may also be related to obesity [23
]. In one study, supermarkets were on average 1.15 miles further away for residents of black compared with white neighborhoods [37
]. In another study, researchers estimated that residents of low-income neighborhoods would have to travel more than 2 miles to have access to the same number of supermarkets as residents of higher-income areas [32
]. Our findings for actual travel distances for food indicated that local access to foods around the home is less frequent than access to foods along routes that occur as part of people’s everyday lives. This may be the result of home environments devoid of local food outlets. Examining accessibility along common routes requires a completely different measurement strategy than focusing only on residential neighborhoods and could include use of GPS devices which track individuals across multiple locations and routes [38
]. This is consistent with current tour based approaches to modeling and predicting travel behavior where food outlet visits are often a mid tour stop [20
Origin and destination environment, type of tour, day of week, age, gender, income, ethnicity, vehicle access and obesity status were all related to visiting a grocery store. Home environment, day of week, type of tour, gender, income, education level, age, and obesity status were all related to likelihood of visiting a fastfood outlet. Many of the same results were seen for the grocery store but operating in the opposite direction. For example men were more likely to visit a fastfood outlet and less likely to visit a grocery store, and older adults were more likely to visit a grocery store than a fastfood location. Fastfood outlet visitation (and dining out overall) may represent a less healthy lifestyle with mostly high fat processed foods available, and grocery store visits may represent a healthier lifestyle because fresh fruits and vegetables are available.
More trips were taken to fastfood on working days than non working days (and vice versa for grocery stores). In particular, a break during the work day was likely to include a fastfood trip, as was the journey to work at the start of the day. This suggests that when participants are pressed for time they resort to stopping for fastfood. Interventions could target these particular trip habits and suggest preparing a healthy breakfast and lunch at home and taking it to work to avoid such unhealthy stops or alternately the provision of healthful food options by employers.
While it is now possible to order healthier options at fastfood outlets, the relationship between obesity and fastfood outlet visitation suggests that patrons are still purchasing high fat foods. Continuing to work on programs to provide healthier options where stops are made is important. One study found that visiting a fast food restaurant was a significant predictor of higher BMI and visiting a grocery store a significant predictor of lower BMI in women [39
Those starting a trip in a neighborhood with few destinations were less likely to travel to a grocery store, but those traveling to a medium accessible environment were more likely to visit a grocery store. This may reflect the availability of parking at many grocery stores, which although surrounded by other destinations, would contribute to the grocery store being in a moderately accessible community. Some unexpected results were found for grocery store visits, including low income participants, non whites and those without a vehicle visiting a grocery store more often than other types of stores. Perhaps those without a car cannot carry as much food with them in a single journey and are more likely to make smaller, frequent trips to the grocery store.
The present study clearly shows that people get food from a variety of locations, many of which are outside of their local community. Therefore, examining the residential food environment alone is insufficient. Many trips to purchase food begin at locations other than home. This suggests studying locations that individuals frequent may be more useful than estimating access to food only around the home; many people spend as much or even more of their waking hours at work. One study found that fast foods restaurants tended to cluster around schools [40
]. To date, few studies have investigated whether the availability of healthy or unhealthy foods outside of the residential environment, along the routes or ‘activity space’ of an individual, is related to diet or obesity [38
]. One small study of migrants did collect a travel and food diary over a week period to assess access to foods locally. [41
]. A recent review also emphasizes the need to study locations other than home neighborhoods and food environments associated with commuting behaviors [42
]. Fruitful locations may be around workplaces or along frequently traveled routes.
Although the literature has documented some disparities in obesity related to differences in healthy food access (6 out of 10 studies) [43
], these studies have not directly assessed where food was purchased. Our study indicated that income, ethnicity, and education was related to distance travelled. Studies suggests that food deserts may be racially driven, not just income related [44
]. Another explanation comes from studies that have also shown that some population groups spend large amounts of time traveling outside of their home environments due to work and care commitments [23
]. Assessing food purchasing patterns outside of home neighborhoods may be particularly important for this group.
The strengths of this study were the large and diverse sample as well as specific measures of places where individuals purchased food. The limitations included use of an activity-based travel survey that relied upon self-report of trips and activities, and limiting the environment to an urban/suburban sample. One study indicated that distances to food stores may be even greater in rural areas [22
]. A two-day travel diary may not be representative or inclusive of the habitual food outlet visitation for an individual or a household. The response rate was lower than for a typical survey study, but the respondent burden for the present study was higher, and there was no information collected about non-respondents. The study did not examine the possible food stores that were available to travel to (and/or their quality), making it difficult to determine whether respondents were making trade-offs regarding distance to/from food outlets and quality; i.e., traveling further to get better quality or cheaper food, or simply choosing to purchase food while on a trip. More complex food tours should be analyzed in future studies, and new techniques from transportation research may be enlightening, such as employing mental mapping of daily travel behavior [45
]. Food trips were not compared to trips for other purposes.
Enumerating food locations accurately [46
] and conducting quality audits [29
] are both labor-intensive processes that would be prohibitive for the 13-county Atlanta region. This study would be strengthened by specific food intake data or food purchasing receipts to confirm what food locations were most impacting participants’ diet and weight. A recent study in the Waterloo Region of Ontario Canada known as “NEWPATH” was patterned after the Atlanta SMARTRAQ study but also included dietary data collection if a location was visited that involved a food purchase [47
]. Exclusion of convenience stores due to the unclear activity criteria was a study weakness as these are common locations for food purchasing. Additional food locations should be considered beyond the five primary ones in the current analyses and inclusion of food locations where food can be grown not just purchased may be informative.
The present study demonstrated that people travelled sizeable distances for food and this distance is related with urban form. Results strongly suggest that researchers need to employ different methods to characterize food environments than have been used to operationalize built environment in studies of physical activity. Further, food is most often purchased while traveling from locations other than home, so future studies should assess the food environment around work, school or other frequently visited destinations, as well as along frequently traveled routes. Increasing our understanding of travel patterns to purchase food is important for improving our health and the health of our environment.