Many food-policy advocates point to a lack of access to healthy food as a singular cause of obesity. Food deserts, defined "as urban neighborhoods and rural towns without ready access to fresh, healthy, and affordable food," are often painted as the root cause.

The USDA uses census-tract data, including a requirement that residents fall below certain minimum figures for income and access to food, to determine if an area qualifies as a food desert. Low-income areas must have either a high poverty rate or low median family income to qualify, while lack of access means "that at least 500 persons and/or at least 33 percent of [an urban] census tract's population live more than one mile from a supermarket or large grocery store[.]" Federal government policies then make aid available to try encourage more food availability.

While that's the federal government's goal, not everyone is on board. In recent years, discussions pertaining to food deserts have become increasingly contentious. Some studies contend food deserts don't exist.

Others studies acknowledge they may exist, but have questioned their link to obesity.

"Getting fresh fruits and vegetables into low-income neighborhoods doesn't make poor people healthier," wrote Heather Tirado Gilligan in a Slate piece earlier this year.

Still more research has declared the impact of food deserts on the health of residents to be nearly irrelevant. A 2013 RAND study, for example, revealed that low-income urban 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," according to a New York Times report. "And there is no relationship between the type of food being sold in a neighborhood and obesity among its children and adolescents."

A Gallup report on the RAND study notes "a lack of access to food in and of itself doesn't matter when it comes to obesity, it only matters if Americans are also low-income."

And then there's the radical notion that the food people ultimately choose to eat—even when faced with nearby healthy food options—"could also be due to people's shopping and eating habits."

Even the USDA itself, in a 2010 report on food deserts it delivered to Congress, admits policy impacts have proven "modest." The report acknowledges "many other factors… contribute to obesity and… increased consumption of healthy foods may not lead to weight loss."

But many advocates seem unfazed by the research.

Meanwhle, the Obama administration's own centerpiece program, the Healthy Food Financing Initiative, "has distributed more than $500 million to increase fresh food access" in food deserts across the country, notes Gilligan.

It's part of Michelle Obama's "ambitious" plan, which she launched in 2010, "to eliminate food deserts in America completely in seven years."

The HFFI program awards tax credits, grants, and technical assistance in order to eliminate all of America's food deserts by 2017.

Has all that funding and attention gotten results? Apparently not.

"Unfortunately, more fresh food closer to home likely does nothing for folks at the bottom of the socioeconomic ladder," writes Gilligan.

While the debate over the existence and impact of food deserts continues, I've long wanted to look critically at a food desert. While I've been to many urban and rural areas classified as food deserts over the years—and actually did my grocery shopping at a Walmart located inside a Fayetteville, Arkansas-area food desert—I've never sought to assess just what food offerings are available inside a food desert.

Seeking to address that deficit, earlier this week I took a group of students enrolled in my American University food policy course to the area around Washington DC's Catholic University. According to the USDA's food desert locator tool, the university's campus lies smack in the middle of a food desert. While this brief field trip could hardly be considered rigorous scholarly research—or a statement on anything but the space I visited—the trip did reveal to me some notable facts.

The first thing I noted in looking at maps before the trip is that the tract is virtually enveloped by government-owned property. Just west of the tract sits the U.S. Armed Forces Retirement Home. To the north sit two parks and a military cemetery. To the east lies rail and subway tracks. Even if a private developer wanted to purchase land—say, to build a grocery store—none appears to be available.

The university brags that students "never go hungry," thanks to a host of convenient options, which include a dining hall, two cafes, a food court, and a small market. The market—in the same building as a Starbucks and the dining hall—sells produce, including fruits like grapes, pomegranates, and Asian pears.

Catholic requires all freshmen and sophomores both to live on campus and to purchase a school meal plan. Meanwhile, the university doesn't guarantee on-campus housing for upperclassmen. In fact, the university has a lottery in place for the limited number of spots available to upperclassmen. Taken as a whole, this means that younger students eat most of their meals on campus, and upperclassmen likely eat most of their meals away from campus. And none of the Catholic students have much of a need for a grocery store in the area.

Off campus, one needn't look too hard—or travel too far—to find groceries. The Yes Organic Market, about a ten-minute walk from campus—just outside the food desert tract—features a wealth of organic produce and other food options. (It's worth noting that the local Yes market chain appears to have taken advantage of HFFI grants to open in some underserved areas.) But those options—like the produce sold on campus—were expensive. About half of my students said they'd be willing to walk to the organic market to shop for groceries. Others said they wouldn't make the trek and would prefer to eat on campus.

A sign just off campus also noted the presence of a local weekend farmers market. Other nearby grocery options include a Walmart grocery store, located two miles from campus. Meanwhile, grocery delivery services like Peapod are available to bring food to those who prefer to order online—and who can't or won't go to the grocery store.

If those options don't suffice, the fact the area is also located next to two subway stops and at least one bus line means people in the area are mobile. One set of Catholic students, in fact, told my students that they often travel by subway to the Whole Foods at George Washington University to buy their groceries.

Together, I found these facts illuminating. The census tract surrounding and including Catholic University may be a food desert by USDA definitions. But students and residents off campus alike have a host of options for buying fresh produce.

The minimum USDA income and access requirements for residents in this food desert seem problematic. College students tend not to be earners. Mandatory meal plans, easy transportation, and online buying options make the term "access" seem largely irrelevant.

People who live in areas that don't have grocery stores may have to work harder to eat healthier. People who live in areas with more choices have (unsurprisingly) more choices. The term "food desert" may be useful for classifying generally the food offerings available in an urban or rural environment. But—at least in the case of the food desert I visited this week—the term isn't terribly useful when it comes to describing a specific tract.