Linking fast-food proximity to obesity

Location is everything ­— a truism that goes for fast food as well as real estate

| 12 March 2009

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 Berkeley economists who calculated that students with temptation that close at hand 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 somewhat farther away from their schools — a quarter-mile to half a mile —and no correlation between obesity and the presence of non-fast-food restaurants near a school, indicating that their findings reflect more than increases in local demand for restaurants in general.

While only 7 percent of Calif-ornia's high schools have a fast-food restaurant within a tenth of a mile, 65 percent have one within half a mile. Schools in the first grouping tend to be in poorer or urban neighborhoods, have more Hispanic students, slightly more students eligible for free lunches, and lower test scores — and also have a higher-than-average incidence of obesity among their students, according to the study, "The Effect of Fast Food Restaurants on Obesity," just published by the National Bureau of Economic Research (NBER).

The researchers — Berkeley economists Stefano DellaVigna and Enrico Moretti, economist Janet Currie of Columbia University, and economist Vikram Pathania, who recently earned his Ph.D. from 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.

"Our results imply that policies restricting access to fast food near schools could have significant effects on obesity among schoolchildren, but similar policies restricting the availability of fast food in residential areas are unlikely to have large effects on adults," their report concludes.
Obesity among children ages 6-19 in the United States increased from about 5 percent in the early 1970s to a whopping 16 percent in 1999-2002 — a period during which the number of fast-food restaurants doubled.

Access to transportation for young people — more specifically, the schoolday lack thereof — may play a role in their dietary choices. "If you look out the window from your classroom and see a fast-food place," says DellaVigna, "it's kind of tempting to go over there."

Fitness facts and a fast-food map

The economists in the NBER study used a detailed dataset showing the exact location of restaurants belonging to the top 10 fast-food chains, independent pizza and burger restaurants, and non-fast-food outlets.

They also examined a decade's worth of records of California's 9th graders, tapping into a wealth of fitness facts about the students who — like their counterparts in 5th and 7th grades — must take a physical exam in the spring. Ninth-graders are tested for their aerobic capacity and upper-body and abdominal strength, and undergo body-fat measurements that indicate obesity.

That information was merged with data collected by the National Center for Education Statistics — such as a school's racial mix and the percentage of its students who qualify for free lunches — and with 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.

The NBER study bolsters support for the notion of a 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.

"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 that most in the industry will follow McDonald's, reporting hefty earnings as cash-strapped consumers seek out cheap eats.