The 100 Mile Diet movement claims that eating only food produced within 100 miles of your home will make you happier, healthier and a better environmentalist (or something like that). Of course, the inventors of this fad live in Vancouver, where it is easy to grow many kinds of food for most of the year. Since I live in Edmonton, I couldn't eat anything produced further south than Red Deer (no more Taber corn). Some people also question whether it is better to eat local produce that requires special growing conditions (local hothouse tomatoes, for example) than just to ship in produce from regions where it will grow easily (field tomatoes from BC). Apparently the local produce can actually require more energy to get to your table.
While this movement probably seems overly restrictive to many northern gardeners, you can still feel smug about saving the environment if you try the Zero Mile Diet. Getting as much of your food as possible from your own backyard (or apartment patio, or windowsill) is probably better for the environment than anywhere else. This type of small-scale food production makes it much easier to avoid toxic pesticides, the pest and disease problems associated with monocropping, and the consumption of fuel in cultivation and shipping. A small garden can also use less water and fertilizers than large farms to produce the same amount of produce, and as demand for farmed produce does not increase, less wildlife habitat needs to be converted to farmland. Growing your own food also provides the freshest food possible, meaning it is healthier and tastier, as well as allowing you to try hard-to-find varieties and foods, and maybe even save money while improving your quality of life.
So grow as much of your food as you can (or feel like), but I think it's okay to indulge yourself in a banana once in a while.