Our study provides some evidence to support an association between the food environment and fast food purchasing. In areas that that were in the highest tertile of the healthy FES, both infrequent and frequent fast food purchasing was less likely though this was only the case for infrequent purchasing after including the unhealthy FES in the analytical models. Surprisingly, frequent purchase of fast food was also less likely in those areas that were in the highest tertile of the unhealthy food scores, however this relationship did not remain significant after adjustment for the healthy FES. It is possible that because 73% of those in the highest healthy FES tertile also lived in the highest unhealthy FES tertile that it was difficult to distinguish the independent effect of the healthy and unhealthy FES. However, we did find that those living in areas that had a higher unhealthy FES than healthy FES were more likely to purchase fast food infrequently (compared with never), although there was no evidence to support an association for frequent purchasing.
The novel approach we used to create the FES allowed us to weight all food stores by their potential contribution to either healthy or unhealthy dietary behaviours rather than providing a simple count of stores. This is an important distinction as, for example, smaller grocers are unlikely to have the equivocal positive influences on food purchasing behaviours as large chain supermarkets. Some researchers commented on the rationale for the weightings they used. For example, it was commented on by one participant that supermarkets were not considered the healthiest food stores to have access to because of the large amount of unhealthy food items they also stocked (for example, crisps, confectionery, soft drinks). This is an important consideration to make, as large supermarkets are often only recognised for stocking large amounts of fresh produce and other healthy foods such as low-fat alternatives and have longer opening hours than other store types thus making them more accessible to people with time constraints. Recent evidence on the high amounts of unhealthy snack food items present in Melbourne supermarkets supports this approach.18
Fast food purchasing as a function of the whole food environment is a largely unexplored topic and few examples exist of studies that have attempted to include multiple food store types, irrespective of the behavioural or health outcome of interest. Our classification of stores is largely consistent with a prior study conducted by Rundle et al.9
In their study, they classified both supermarkets and fruit and vegetable stores as healthy food stores, whereas fast food outlets and convenience stores (our equivalent being ‘convenience food store non-fresh') were considered unhealthy. Importantly, they also categorised a multitude of other food store types in their exposure measure (natural/health food stores, other (non-fast-food) restaurants, medium-sized grocery stores, fish markets, specialty food stores, pizza restaurants, bodegas, bakeries, candy and nut store, meat markets), although no weightings were applied.
The presence of healthy food outlets9
and chain supermarkets10
were previously found to be associated with a lower BMI and lower prevalence of obesity. Although those studies did not explore dietary outcomes, the findings suggest improving healthy food access may be as important as limiting unhealthy options. Additionally, prior research has also shown that having greater access to unhealthy food stores in the form of fast food outlets and convenience stores was associated with a lower consumption of fruits and vegetables among children.19
In this instance, the environment creates more opportunity to engage in unhealthy eating behaviours and therefore consumption of fruits and vegetable may suffer as a result. Although it is plausible to also suggest that when people are given healthy alternatives they may be more willing to make the healthier choice or that the opportunities to purchase healthy foods may mean a lower reliance on the convenience that unhealthy fast foods offer, our study provides only limited evidence to support this.
A major strength of this analysis is the inclusion of a comprehensive list of both healthy and unhealthy food stores to represent the full range of food choices available to local residents. Importantly, we also created a system whereby stores were weighted by their potential contribution to healthy and unhealthy dietary behaviours (based on the opinions of experts in the field) and not simply counted. This means of representation is more indicative of the true amount of healthy and unhealthy foods they have access to than a measure that simply considers the presence of either a fruit and vegetable store or a bakery as providing an equal contribution to food choices. Furthermore, we were able to differentiate between larger and smaller supermarkets based on the number of cash registers within a store; a method that has been used by others to define store size.20
However, we acknowledge that the analysis contained some limitations that must be considered. First, although our approach to creating the scores based on the ratings of experts is a novel approach, the number of researchers involved in this process was small. Second, a more objective score could be created using within-store audits. Third, the current scoring method does not provide any flexibility to provide different scores to stores within the same category (that is, all large supermarkets are scored the same despite previous evidence demonstrating differences within supermarket environments).18, 21, 22
Our outcome measure only included fast food consumed at home, which is likely to be an underestimate of total consumption. The fact that we only explored the food environment around home underestimates exposure to the range of environments an individual would interact with. Although we do not capture all consumption and exposures, prior research has shown that over a week, 62% participants in a US study reported eating fast food within 1 mile of their home within a week,23
thus it is plausible our measure captures a reasonable proportion of total fast food consumption and food store exposures. Further, given our outcome measure is based on fast food consumed at home, we believe this increases the likelihood that it was purchased nearby to their household location.
Future studies could explore how the role of food environment, as measured by the FES, impacts on a wider range of dietary outcomes, such as fruit and vegetable consumption, or on the consumption of more nutritious low-fat/high-fibre alternatives of core food products, such as bread and milk, compared with the regular options. It is also important to note that the choice of stores used for this Melbourne-based study may not be applicable to other contexts. This may have contributed to the large s.d. for some store types where researchers from different nations viewed the role of these stores differently. Further research is needed to quantify the potential dietary impact of different store types and this approach would benefit from objective measures on the within-store environment.