The trend toward local, seasonal eating is certainly great news for local farmers and the environment. But depending on where you live and the time of year, a strictly local diet might not always be the best health or financial choice, since limited availability makes a healthy, varied, and affordable diet tough.
Eating locally can ensure quality and cleanliness of food, and it usually means that the food is organically grown. When you eat locally, whether from a farmer's market or direct from the farm, you also created a partnership with the farmer. You can visit the farm, ask questions about growing and harvesting practices, and in some cases even be part of the seasonal production. You can also opt to join a local CSA (Community Sponsored/Supported Agriculture), a fairly new model of food production, sales and distribution that delivers a weekly basket brimming with fruit, vegetables, flowers, and herbs. Most CSA farms partner with bread, cheese, egg and meat producers, as well. Check out www.localharvest.org to find your nearest CSA.
But back to your question. The real data behind whether locally grown, organic produce is better in strictly nutritional terms is more difficult to find. To our knowledge, it has not been definitively proven either way. Not even the USDA, which certifies food as organic, claims that it is more nutritious. Produce, however, definitely changes once it is picked. Temperature variations, transport time, and exposure to light all expedite deterioration, which means changes in water content, texture, color, microbial content, and ultimately, nutrient quality and content. Simply stated, the closer you live to where it was grown, the better it will most likely be for you.