In 2003, 41% of family food budgets in the USA were spent eating out.1
Fast food sales, which comprise more than 41% of restaurant sales, have increased from $16.1 billion in 1975 to $123.9 billion in 2003,1
and because consumption of fast food is associated with higher body mass index (BMI) in adults and children,2–4
there has been recent interest in understanding whether fast food consumption is causally related to the US obesity epidemic.2–7
It is unclear whether proximity to fast food outlets can explain the higher prevalence of obesity in low-income minority populations. Studies examining the location of outlets in relation to at-risk populations in Europe and the USA have yielded mixed results8–14,37,41–43
; furthermore, the association between access to fast food restaurants and obesity has also been mixed.5,7,15–17,37–40
Mehta and Chang5
found an association between higher US county concentration of fast food restaurants and increased BMI; they also found that higher county concentration of full-service restaurants and total restaurants (fast food
full service restaurants) were associated with lower BMI. In another US study, Chou et al.7
found that higher concentration of total restaurants at the state level made the largest contribution to increasing weight. All the other cited studies showed no association between obesity and geographic access to fast food restaurants.
One reason for the mixed results in fast food studies may be due to how access and proximity are measured. Studies have used distance to the nearest fast food site15
and number of fast food outlets per 1,000 people16,17
to measure fast food exposure. Distance to the closest fast food site may be insensitive in measuring spatial accessibility in congested urban areas where one may find many fast food outlet options at similar distance from any reference point. Additionally, fast food per population measure is a supply ratio that grossly compares supply of fast food between different areas, which may misrepresent access because it does not incorporate any measure of distance or travel impedance.18
Concentration of fast food outlets as measured by locations per roadway mile may be a more appropriate measure of fast food access in modern urban environments because it accounts for spatial dispersion,19,20
which captures not only the fast food environment but its interaction with people.21
This may be particularly relevant in cities where individuals traverse the city and access fast food outlets along major and minor arterial roadways. Studies of alcohol outlet density measures have used alcohol outlet stores per roadway miles to show an association with violent assaults and with alcohol-related motor vehicle accidents.22,23
Related to this issue, fast food associations with BMI may not have been seen if factors, such as car ownership, that reduce barriers to alternative healthier food choices were not taken into account. Early studies have shown that neighborhood associations with health outcomes are stronger in individuals who do not own cars.27,44
No study has yet examined the role of car ownership in the association between access to fast food and obesity.
In this multilevel study, we examined whether fast food and general restaurant access, defined as the number of fast food outlets (or restaurants) per roadway miles per residential census tract, is associated with neighborhood socioeconomic levels and the BMI of its residents and whether this association is moderated by car ownership.