I love the farmers' market. A victim of my own post-yuppie childless female demographic, I can't help but cherish a vision of myself in a summer dress, basket tucked in the crook of my elbow, sashaying between stalls of heirloom tomatoes, wildflowers, and artisanal pork products. In this fantasy it is 7:30 on a brilliantly sunny Sunday morning, and all the grizzled farmers and jolly butchers know me by name.

This is, of course, an absurd delusion. What really happens most weeks is that I sleep in, then pick up a shrink-wrapped bundle of green beans and an equally shrink-wrapped Tyson chicken at the Safeway.

While I weep for the lost aesthetic experience, I'm not worried about endangering my own virtue, my health, or the health of the planet if I'm a little hung over from Saturday night's festivities or if it happens to be raining when I wake up. Because there simply isn't anything like conclusive evidence that shopping at the farmers' market will save me (or the environment) from such heartaches.

I'm sure you've heard: Killer tomatoes are attacking America as we speak. The New York Times editorialized that we "should not have to wait until the next food scare before Washington comes to the rescue." The Food and Drug Administration (FDA) is doggedly eliminating possible culprits state by state. But not all tomatoes are equally terrifying, the FDA has been careful to point out. Cherry or grape tomatoes are fine, as are homegrown tomatoes.

This last bit has the "eat local" crowd crowing. Locavore (word of the year 2007!) logic goes like this: Those big factory farms are awash in God knows what kind of creepy-crawlies. Tomatoes are picked in one place, washed in another, packed elsewhere, and shipped hundreds or even thousands of miles. Of course they're going to get dirty! Far better, say the locavores, to eat food that is grown within a small radius, say 100 miles of your home. Buy at farms and farmers markets. Get to know your local producers and only shop with the ones you trust. Grow your own! An appealing prospect, to be sure. But the gap between homegrown and farmer's market may be larger than the gap between farmer's market and supermarket.

"As a scientist, I cannot say smaller is better. It's just not that simple," Martha Robert, a microbiologist at the University of Florida Institute of Food and Agricultural Sciences and a safety adviser to the Florida Tomato Growers Exchange, told Newsweek. "The large packers we have are extremely stringent with sanitizing techniques and measures to prevent cross-contamination, but if someone makes a mistake when they're mixing or dicing large quantities, the problem is going to be larger too," she explains. "But sometimes a small grower has been doing something for years, and [they] don't know they're putting themselves at risk."

Put another way, anyone who has ever been in one of New York's independent corner greengrocers, or an unaffiliated rural grocery store knows that small and local are no guarantee of higher hygiene standards. Some big operations are squeaky clean, others breed disease. Likewise with the little guys. As I write, the feds are fingering a couple of growers and maybe a restaurant chain as the culprits after clearing thousands of tomato producers.

Small can be beautiful, but it's no guarantee of better hygiene or virtue. Accidents happen. Sometimes pigs shit in inconvenient places or someone fails to wash his hands on little farms, too.

Because advocates of local eating conflate health and environmental issues on a regular basis, allow me to briefly do so as well. Much of the warm glow of farmers' market virtue comes from a growing concern about something called "food miles"—when a box of grape tomatoes has to travel hundreds of miles to get to your plate, surely the number of carbon-belching, petroleum-powered vehicles involved becomes unacceptable. So even if you still might end up calling Ralph on the big white phone thanks to some tainted tomatoes, at least you'll be able to tell him you weren't contributing to global warming, right?

Just in time for summer, a new study finds a serious hole in the food miles concept: In terms of total carbon output, what you eat matters a lot more than where it came from. Swapping out chicken for red meat every now and then can eliminate just as much carbon as eating entirely local. Going further still, several studies have come up with variations on this somewhat counterintuitive conclusion: shipping spring lamb on the slow boat from New Zealand may actually produce less carbon than hopping in the minivan for a family trip to pick up some locally-raised lamb shanks from the farmer outside of town, or a drive to the farmers' market.

Because I'm a late sleeper, I often manage to emerge, unshowered and basketless, just as they're shutting down the farmers' market in my neighborhood. The site is no longer a magical, vegetable version of Willy Wonka's Chocolate Factory. It's just a parking lot with a burst glass container of fresh-from-the-cow (potentially unpasteurized) milk, a Port-a-Potty in the corner, and nowhere to wash your hands. The snarl of shoppers' cars and farmers' old diesel trucks that chokes the neighborhood on market days is just clearing up. The farmers' market is marvelous enough without all the trappings—while I'm sad that once again this week I won't befriend a jolly butcher, I remain unconcerned about my gastronomic virtue or the relative threats to my guts.

Katherine Mangu-Ward is a reason associate editor.