Portions -- not fast food -- may lead to wider waistline, study shows

February 2, 2009 By Mike Hughlett

With all the finger-pointing at fast food as a factor in America's obesity epidemic, you'd think people would be fatter where the supply of restaurants is greater--that is, neighborhoods teeming with burger joints, chicken shacks and so on.

But according to Northwestern University finance professor David Matsa, you would be wrong - and that has implications for government policy.

Matsa, along with Michael Anderson at the University of California-Berkeley, this month unveiled a study, "Are Restaurants Really Supersizing America?" - a nod to "Super Size Me," a 2004 documentary about a man who ate only McDonald's food for a month.

Matsa and Anderson acknowledge there's a well-known body of research showing that the frequency of eating at restaurants is correlated with greater accumulations of body fat. But is an abundant supply of restaurants actually causing fat levels to mushroom?

To answer that, the professors measured the restaurant habits and obesity levels of people who live near interstate highway exits and entrances in rural areas. Here, in order to serve travelers, restaurant supply often greatly outstrips local demand.

Matsa and Anderson compared restaurant consumers who lived zero to 5 miles from an interstate to those who lived 5 to 10 miles away.

They found that people who lived right off the interstate indeed ate much more often at restaurants than those who lived farther away. But using a battery of databases, Matsa and Anderson concluded that denizens of interstate towns were no fatter than folks who lived just a few miles away.

For obesity data, the professors turned to an ongoing, large-scale telephone survey of health behavior conducted by the Centers for Disease Control.

Matsa said the findings indicate government policies aimed at restricting restaurants - a ban on new fast-food outlets in a portion of Los Angeles, for example - may not work.

People who eat more at restaurants simply may eat more generally, including at home, Matsa and Anderson said. If costs are added to restaurant meals through restrictions like putting extra taxes on fattening food or making diners drive farther to find a fast-food joint, restaurant patrons may simply shift to sources of cheap calories elsewhere, they said.

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