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When you go to the store and pick up a fresh bunch of "organic" asparagus, and the tag on the asparagus says it's from Chile, are you operating under the assumption that your eating habits are sustainable? If so, let me recommend "The Omnivore's Dilemma" to disavow you of that notion forthwith. "Organic" does not = sustainable. It just means they're not pumping synthetic and harmful pesticides into the soil and water. It doesn't mean they're not expending a huge amount of fossil fuel both to plant and harvest the produce and get it to your local store.
The only way you could possibly eat sustainably is to grow all your fruits, vegetables, starches and proteins in your backyard--and even then, I'd be curious how many trips you'd have to make to the gardening store to buy fertilizer and "soil amendments" (which of course come encased in plastic bags). I'm trying it myself and, even with my own compost heap, I still have to buy a number of things (chief among them, the plants and seeds, although hopefully that's just a one-time expense).
The idea of a self-sustaining garden that produces all the calories and nutrients needed by a human being is explored in detail in the books available off of these two websites, and I highly recommend them to anyone interested in sustainable food production--but even these folks don't claim to have achieved 100% sustainability:
http://www.edibleforestgardens.com
http://www.growbiointensive.org
Also--any of you vegans happen to own or maintain grass lawns? Because those are bad, bad, bad. Check out the Edible Forest Gardens book. I mean, what's next, you're going to tell me you mow it with a gas-powered mower? Heaven forfend.