When a big public policy issue emerges, commentary tends toward solutions. Advocates for different solutions make all sorts of causal claims about why the problem has occurred and what could fix it. Often, though, it turns out there was never any problem to begin with.

Is “food deserts” one of these cases? A recent New York Times article suggests yes.

It has become an article of faith among some policy makers and advocates, including Michelle Obama, that poor urban neighborhoods are food deserts, bereft of fresh fruits and vegetables.

But two new studies have found something unexpected. Such neighborhoods not only have more fast food restaurants and convenience stores than more affluent ones, but more grocery stores, supermarkets and full-service restaurants, too. And there is no relationship between the type of food being sold in a neighborhood and obesity among its children and adolescents.

Within a couple of miles of almost any urban neighborhood, “you can get basically any type of food,” said Roland Sturm of the RAND Corporation, lead author of one of the studies. “Maybe we should call it a food swamp rather than a desert,” he said.

I have to admit I’m biased toward believing these studies, because the idea of contradicting an “article of faith” embraced by celebrities appeals to me. But was there ever any empirical evidence of food deserts to begin with?

It is unclear how the idea took hold that poor urban neighborhoods were food deserts but it had immediate appeal. There is even an Agriculture Department “food desert locator” and a “National Food Desert Awareness Month” supported by the National Center for Public Research, a charitable foundation.

But, Dr. Lee said, studies lending support to the idea tended to be limited by methodological difficulties.

For example, some researchers looked at neighborhood food outlets but did not have data on how fat residents were. Others examined small areas, like part of a single city and extrapolated to the entire nation. Others had a different problem. They looked at much bigger areas like ZIP codes, which include people of diverse incomes, making it hard to know what happened in pockets of poverty within those regions.

Some researchers counted only fast food restaurants and large supermarkets, missing small grocers who sold produce. Some tallied food outlets per 1,000 residents, which made densely populated urban areas appear to have fewer places per person to buy food. A more meaningful measure, Dr. Lee said, is the distance to the nearest stores.