Overall, about 15% OF U.S. energy goes to supplying Americans with food, split roughly equally between the production of crops and livestock, and food processing and packaging. David Pimentel, a professor of ecology and agricultural science at Cornell University, has estimated that if all humanity ate the way Americans eat, we would exhaust all known fossil fuel reserves in just seven years.

The implications of agricultural energy use for the environment are disturbing. According to the Intergovernmental Panel on Climate Change, agriculture contributes over 20% of human-caused greenhouse gas emissions, including more than 20% CO2, 55% of methane and 65% of nitrous oxide. In addition, our energy-intensive agriculture industry contributes substantially to soil erosion, loss of wildlife habitat, degradation of water quality from chemical runoff and causes other adverse environmental impacts.

Much of the energy embedded in our food comes from growing grains that require further processing to be eaten. Producing a 2-pound box of breakfast cereal, for example, requires the equivalent of burning half a gallon of gasoline.

Eating high on the food chain is even worse. Eating a carrot or an apple gives the diner all the caloric energy in those foods, but feeding these foods to a pig reduces the energy available by a factor of 10. That's because the pig uses most of the energy just staying alive, and stores only a fraction of the energy in the parts we eat. All told, it takes 68 calories of fossil fuel to produce one calorie of pork, and 35 calories of fuel to make one calorie of beef.

Interestingly, the path to reducing the energy intensity of the food system dovetails nicely with the path to a healthy and nutritious diet. It can be summarized in three simple suggestions.

First, eat lower on the food chain. That means more fruits and vegetables, and fewer meats and fish. Meats, poultry and fish contain necessary proteins, but most American diets contain too much protein - about twice the recommended amount. Since 80% of the grains go to feeding livestock, the amount of energy used indirectly to support our diet of double bacon cheeseburgers is staggering. And, if you do eat meat, then try to avoid animals grown in feedlots or factory pens. They take far more energy calories to raise than free-range, grassfed critters, which have only about a third of the embedded energy.

Second, eat more fresh foods and fewer processed foods. Fruits and vegetables again, but also whole grains, legumes and other less-processed foods, have much less embedded energy. In general, the more packaging, the more processing - and the more energy associated with its production.

Third, buy local. Incredibly, the food items on U.S. grocery store shelves have traveled an average of 1,500 miles. And some foods are much worse. Table grapes grown in Chile, transported by ship to California and shipped by truck to Iowa have traveled over 4,200 miles. In response, some agricultural scientists have proposed ecolabeling programs based on CO2 rankings or broader lifecycle assessments.

These analyses provide better information than just miles traveled. For instance, because they travel by air rather than by ship, Hawaiian pineapples are among the most carbon intensive of foods, contributing about 40 pounds of CO2 per pound of pineapple. That is about 10 times the next highest figure among the foods studied.

In my hometown of Portland, Oregon, individuals and businesses alike are starting to recognize and respond to the public's concerns about fossil food. Grocery stores featuring locally grown and organic products are common. Farm stands, farmer's markets and community-supported agriculture operations are thriving. Here, even fast food restaurants are using local and organic ingredients.

For instance, Burgerville is a local chain that buys exclusively Oregon Country Beef, the branded product of 40 family ranches in the region that produce an all-natural product made without hormones, genetically modified grain or any animal byproducts. Burgerville promotes the fact that customers can trace the source of their food from ranch to table - and play a role in sustaining the local agricultural economy. Another local company, Hot Lips Pizza, worked with a group of Northwest farmers to create a Food Alliance-certified local market for organic wheat and flour, providing customers with pizza that is sustainably grown. It also is really, really tasty.

After all, you are what you eat.

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Thomas Starrs is Chair of the American Solar Energy Society. Contact him: chair@ases.org