It seems that the increase in the number of fast food restaurants when compared to full service restaurants has contributed to the raise in obesity.
The findings are based on data from 5 years of the Behavioural Risk Factor Surveillance System (BRFSS), an annual telephone health survey of the American adult population and the 2002 U.S. Economic Census.
The researchers examined the link between restaurant availability and weight status in 544 US counties. This resulted in over 700,000 BRFSS respondents, representative of approximately 75 percent of the 2002 US population.
They found that a higher total restaurant density is significantly associated with lower weight status.
However, when the restaurants are split into components: fast food and full service, a higher full-service restaurant density is significantly linked to lower weight status while a higher fast-food density is linked to higher weight status.
Neil Mehta, MSc, Population Studies Center, University of Pennsylvania and Virginia W. Chang, MD, PhD, University of Pennsylvania School of Medicine, said: "The results reported here demonstrate that the restaurant environment is associated with weight status net of individual- and county-level factors.
"The relationship is complex, suggesting that the restaurant environment's influence goes well beyond a simple positive association between restaurant density and weight status. Rather, different components of the restaurant environment exhibit differential associations with weight status.
"Individuals residing in areas with a high density of total and full-service restaurants exhibit lower weight status, possibly indicating that these areas possess a more advantageous eating environment. Those who reside in areas possessing a higher relative number of fast food to full-service restaurants have a higher weight status.
"Hence, the relative availability of alternative types of away-from-home eating establishments may most accurately capture the set of food choices available to individuals and may be salient in determining eating behaviours and ultimately weight status.
The findings therefore support the notion that fast-food restaurants are a contributor to obesogenic environments.
The study is published in the February 2008 issue of the American Journal of Preventive Medicine.