Correlation/causation misfire? Sure, unless you want to believe that the government should put up a fresh food stand within a half mile of your house to keep you from becoming obese.
John Spence from the University of Alberta, Canada, worked with a team of researchers to study associations between the 'Retail Food Environment Index' (RFEI) and levels of obesity. He said, "The RFEI is based upon a ratio of the number of fast-food restaurants and convenience stores to supermarkets and specialty food stores in a given radius around a person's house. We've shown that it correlates very well with the odds that that person may be obese."
The availability of fast food and scarcity of outlets for natural ingredients within a half mile of a person's home was shown to be associated with weight, while the RFEI within a one mile radius did not have the same effect. The researchers claim that this demonstrates that the proximity of the unhealthy environment is an important risk factor for obesity.
According to Spence, "These findings may help explain the observation that geographic concentration of fast-food restaurants is associated with mortality and hospital admissions for acute coronary events in Canada".
Fast-food is cheaper and more energy-dense per measure of weight than other healthier foods such as fruits and vegetables that are purchased in a grocery store. If governments want to reduce people's intake of these energy-efficient, but ultimately unhealthy 'meals', the authors recommend that they intervene to limit the creation of areas where tempting junk-food outlets are so much more prevalent than other shops.
They write, "A plausible policy option for decreasing the prevalence of obesity among adults is improving the retail food environment, possibly through zoning by-laws".
Article: 'Relation between local food environments and obesity among adults', John C Spence, Nicoleta Cutumisu, Joy Edwards, Kim D Raine and Karen Smoyer-Tomic, BMC Public Health (in press)