The U.S. local food movement -- which used to be elite, expensive and mostly coastal -- has gone mainstream, with a boost from environmentalists who reckon that eating what grows nearby cuts down on global warming.

But do food miles -- the distance edibles travel from farm to plate -- give an accurate gauge of environmental impact, especially where greenhouse gas emissions are concerned?

"Food-miles are a great metaphor for looking at the localness of food, the contrast between local and global food, a way people can get an idea of where their food is coming from," said Rich Pirog, associate director of the Leopold Center for Sustainable Agriculture at Iowa State University.

"They are not a reliable indicator of environmental impact," Pirog said in a telephone interview. "What one would want to do is look at your carbon footprint across a whole food supply chain."

The problem with food-miles is that they don't take into account the mode of transport, methods of production or the way things are packaged, and all of these have their own distinct impact on emissions of carbon dioxide, a climate-warming gas.

Take the case of the well-traveled Idaho potato and its closer-to-home cousin from Maine. For a consumer on the U.S. East Coast, the Maine potato seems the winner in the local food derby.

But Maine potatoes get to market by long-haul truck while Idahos go by train, a more energy-efficient mode of transportation, so they have a smaller carbon footprint even with a larger number of food-miles.

The example is easily transposed to Europe, Pirog said, noting the relative environmental impacts for a Stockholm consumer in tomatoes grown in a Swedish greenhouse compared with field-ripened tomatoes imported by ship from Spain. The Spanish tomatoes are more Earth-friendly.

FOOD, FUEL AND FREEWAYS

The idea of food-miles, or more properly food-kilometers, began in Sweden and Britain, but Pirog and others at the Leopold Center started looking into the matter in the United States in 2001 in a paper called "Food, Fuel and Freeways," available online at http://www.leopold.iastate.edu/pubs/staff/ppp/index.htm.

It is now so commonplace for Americans to opt for local versus regional or national food supplies that sophisticates feel free to make fun of the movement, as The New Yorker did in its October 8 edition.

"We think it's terribly important that you meet the people responsible for the food you're eating tonight," reads the caption on a cartoon showing a pair of wary-looking diners, surrounded by a smiling waitress and basket-bearing farm-folk with their produce and livestock.

The United States came late to the local food movement, except for high-end eateries that featured their offerings' provenance as a selling point in the 1970s. Until then, imported food was considered a status symbol, no matter what condition it was in when it finally arrived at the table.

Before that, most Americans unthinkingly ate local food out of simple necessity. If your great-grandmother wanted a tomato in winter, she probably opened a home-canned jar rather than picking an Israeli-raised specimen at the supermarket.

Another difficulty with the food-miles measurement is that the most accurate versions of this calculation deal only with produce, not with prepared foods that contain many ingredients from many sources.

NOT JUST FOR GRANOLA BAR FOLKS

This is changing, Pirog said, reached outside a conference on this issue in Portland, Oregon. Researchers in Europe and Japan are leading the way in figuring out how to make these complex calculations, and Pirog noted that Europe and Japan are parties to the Kyoto Protocol which mandates reductions in greenhouse gases. The United States is not.

The calculus is not always environmental; most locavores say taste comes first, while some maintain locally produced products are safer or more nutritious.

Others, like restaurateur Barry Eastman, say local provisions make economic sense for the businesses that use them and the farmers that raise them.

As the owner of Rudy's Tacos in Waterloo, Iowa, Eastman has been seeking out local suppliers for a decade, with 70 percent of his food produced in Iowa. This is not as obvious as it may seem: while Iowa is dense with farm fields, most are planted with commodity crops like soybeans and feed corn -- a circumstance that makes parts of the state food deserts. Corn, corn everywhere, but not an ear to eat, if you're a human.

"You'd be surprised at how many people want to know where their food is coming from," Eastman said by telephone. "It's not just the granola bar folks, everybody's starting to get into it."

In his case, the primary driver was flavor, and he found that local chickens made for a better-tasting taco than those trucked in from Alabama in the same load with paper towels and other restaurant staples. The Iowa poultry cost more per bird but less overall because they were meatier, Eastman said.

Tim Schlitzer, executive director of the Food Routes Network, which promotes a national "Buy Fresh, Buy Local" consumer campaign, noted long-term reasons to encourage the locavore movement.

As commodity farming increases in the United States, some regions can lose the ability to feed themselves, Schlitzer said in a telephone interview from Arnot, Pennsylvania.

"Right now, there's a national and international food system," Schlitzer said. "Ten years, 20 years from now, will that still be the case?"

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