Linking fast food proximity to obesity
| 04 March 2009
BERKELEY — Location is everything - and that goes for fast food as well as for real estate.
California's nearly 3 million 9th graders are at least 5.2 percent more likely to be obese if there is a fast food restaurant within a tenth of a mile of their school, according to a new study by University of California, Berkeley, economists who calculated that these students eat 30 to 100 more calories per school day than their non-obese counterparts.
But they found no connection between fast food and obesity if the outlets are a quarter-mile to half a mile from high schools, and no correlation between obesity and the presence of non-fast-food restaurants near a school, indicating their findings reflect more than simple increases in local demand for restaurants in general. Their accompanying analysis of weight gain by pregnant mothers and their proximity to fast food outlets showed a much smaller impact for the moms than for the students.
"Our results imply that policies restricting access to fast food near schools could have significant effects on obesity among school children, but similar policies restricting the availability of fast food in residential areas are unlikely to have large effects on adults," their report concluded, noting that transportation limits on youths may be a factor.
Obesity among children ages 6-19 in the United States increased from about 5 percent in the early 1970s to a whopping16 percent in 1999-2002, and the number of fast food restaurants doubled in the same period.
Economists Stefano DellaVigna and Enrico Moretti of UC Berkeley, economist Janet Currie of Columbia University and economist Vikram Pathania, who recently earned his Ph.D. from UC Berkeley - say their work may help guide cities interested in fighting obesity to establish zoning regulations that control how close fast food outlets are placed to schools.
"If you look out the window from your classroom and see a fast food place, it's kind of tempting to go over there," said DellaVigna.
In "The Effect of Fast Food Restaurants on Obesity," just published by the National Bureau of Economic Research (NBER), the economists serve up evidence of the link between fast food availability and obesity. To date, that link has been a matter of speculation, estimation and studies using data sets too small in scale to provide much validity or precision.
They also found that while just 7 percent of California's high schools have a fast food restaurant within a tenth of a mile, 65 percent have one within half a mile. Schools within a tenth of a mile of a fast food restaurant have more Hispanic students, slightly more students eligible for free lunches, lower test scores, tend to be in poorer and urban neighborhoods - and have a higher than average incidence of obesity among their students, according to the study.
"This is a step in the direction of understanding the puzzle of obesity," said DellaVigna.
"The results ... are consistent with a model in which access to fast foods increases obesity by lowering food prices or by tempting consumers with self-control problems," the report said.
And while the current weak economy may slow the near-term expansion of fast food operations, many experts expect most fast food firms will follow McDonald's, reporting hefty earnings as cash-strapped consumers seek out cheap eats.
The economists in the NBER study used a detailed dataset showing the exact geographic location of restaurants belonging to the top 10 fast food chains, independent pizza and burger restaurants and non-fast food outlets.
They also examined records of California's 9th graders for nearly a decade (1999 and 2001-2007), tapping into a wealth of fitness facts about the students who - like their counterparts in 5th and 7th grade - must take a physical exam in the spring. Ninth graders are tested for acceptable levels of aerobic capacity and upper body and abdominal strength, and undergo body fat measurements that indicate obesity.
That information was merged with data such a school's racial mix and the percentage of its students who qualify for free lunches collected by the National Center for Education Statistics and 2000 Census data about family earnings, education and employment. This data helped control for special characteristics of schools and neighborhoods, such as the higher rates of obesity for Hispanic and black youths.
As another control, the economists used 15 years of information from the U.S. National Vital Statistics from Michigan, Texas and New Jersey recording weight gains during pregnancy for more than 1 million women with at least two children.
They found a 2.5 percent increase in obesity rates for these women - especially African Americans and those with a high school education - when fast food was available within half a mile of their homes, but there was no significant difference in rates when the outlets were a tenth of a mile or half a mile away.
Their report can be found online at: http://www.econ.berkeley.edu/~sdellavi/wp/fastfoodJan09.pdf.