Has it ever occurred to you that the vegetables you put in your basket at the supermarket have done more traveling in the last week than you've done in the last year? The next time you go shopping, take a close look at the tiny little labels on each item before you peel them off. It's probably not a surprise that those ripe fragrant nectarines rolled in from California, maybe on the same truck as that mix of tender baby lettuces, and the carrots and broccoli in adjoining bins. Over there, that crisp cabbage started life in Texas. Baby red potatoes and ears of corn? They're from Florida. But wait, try an international flavor: tomatoes on the vine from Canada, onions and mangoes from Mexico. Too North American? How about tangy kiwi fruits from Chile, butternut squash from Guatemala, or apples from China?

As recently as 1970, most of the food we bought at the market came from local growers. In the last 30 years, advances in food distribution and transportation, and consolidation in farm ownership have overridden the constraints of seasonality and local availability. Now, we think of the supermarket as the place where we go to get just about anything. That's because our food comes from just about everywhere.

This new world of universal food availability opens up the possibilities in your kitchen. But if you want guava in your fruit salad, there are some things to consider.

These days, according to the World Watch Institute, food in the United States typically travels between 1,500 and 2,500 miles from farm to plate. That can encompass a trip from the farm to a broker, then to a regional distribution facility and on to the supermarket. Not only is shipping a cost factor, both in dollars and environmental impact, but where food comes from also has an effect on its nutritional value and how it tastes. Research shows that vegetables begin losing nutritional value as soon as they are picked, so the shorter the time from field to meal, the more beneficial they are for you to eat.

Often, when vegetables finally make it to the bins in your supermarket, they have been on the road for as many as 14 days, especially if they've come from another country. That's not to say that the items will necessarily show any wear and tear from all this travel. Supermarket chains with large-scale distribution systems tend to buy produce that has been selected not primarily for its flavor or nutritional value, but for its ability to withstand the handling involved in mechanical harvesting, packing and shipping. Tender fruit that bruises easily, regardless of how fabulous it tastes, won't appeal to a produce manager at Wal-Mart. If it's not going to arrive at the store looking good, that manager won't buy it. As many as half of all tomatoes in the United States are harvested green for shipping, then artificially ripened when they arrive at the supermarket. Studies have found that green harvested tomatoes contain substantially less vitamin C than those that are ready to go into your salad when harvested. Not to mention the fact that recently harvested food is more flavorful than its industrially produced counterparts.

Supermarkets are, first and foremost, massive retailers of a wide range of products, most of which don't stay on the shelf for very long. They require a sophisticated supply system that supports large volume and standardization to assure a steady flow to the shelves. They have complicated pricing models to drive sales of high-profit items. In fact, supermarkets will sell some items at or below cost (commercially raised chicken parts, or in-season corn, for example) to attract shoppers who will also purchase high-profit-margin goods once they are there. Stable costs and reliable supplies are keystones for these big stores.

"It's a challenge for large markets to work with local farmers," explains Judith LaBelle, president of the Glynwood Center, a nonprofit research center based in Cold Spring, that's dedicated to helping Hudson Valley communities resolve the tensions that can arise when rural communities undergo development. "They [supermarkets] are used to getting everything from a relatively small number of suppliers; they're not used to dealing with the vagaries of local weather, etc."