The energy costs of transporting large quantities of fresh produce, even across great distances, are typically less than those required to process, package, and distribute the same baby carrots or lima beans in a can or freezer bag.

Most fruits and vegetables must be cooked or blanched before canning or freezing. These processes not only deplete otherwise nutritious foods of vitamins and minerals but also require substantial energy. For canned goods, most of the invested energy is consumed in the packaging process—manufacturing the steel can and then sterilizing, filling, and sealing it. For frozen foods, most of the energy is used in freezing the product and then keeping it at that temperature from the factory to the freezer section of the grocery store. For both canned and frozen foods, the majority of that energy is supplied by fossil fuels.

Although the long-distance transport of fresh fruits and vegetables also consumes fossil-fuel resources, the lack of processing or packaging means that the quantity of fossil-fuel energy invested in a pound of fresh produce is typically less than the amount invested in a pound of canned or frozen food.

For example, researchers have assessed the average energy required to produce fresh, frozen, and canned corn. The production of one pound of fresh corn requires less than one-sixth the energy necessary to produce a pound of canned corn; fresh requires less than one-eighth the energy needed to produce and store a pound of frozen corn. Based on estimated transport energy, fresh corn would need to be transported nearly 4,000 miles in order to approach the energy consumed in the canning or freezing process. (Shipping an orange coast-to coast from Fresno, CA, to Bangor, ME, is still just 3,340 miles.)

When finally ready to be eaten, canned and frozen vegetables (just like fresh ones) must be cooked. And although any food waste can be composted, the steel can and plastic packaging require yet more energy to transport them to recycling facilities or landfills.

Admittedly, fresh products will always have shorter shelf lives, while canned and frozen goods can be conveniently stored and ignored for months at a time—a godsend for those of us who lack the time for daily market runs or the inclination to cultivate our inner Julia Child. It's still best to buy fresh fruits and vegetables locally when they're available. If this causes you to make more frequent shopping trips, you can conserve transportation energy by combining multiple errands or shopping on the way home from work. And don't forget to bring your own bags to avoid putting more plastic into the landfill.