For greater accuracy, ERS researchers used the survey-based benchmark input-output accounts from 1997 and 2002, rather than the 2007 projections, to discern the largest or fastest growing users of energy and the factors that sparked increased food-related energy use. Between 1997 and 2002, energy use in the U.S. food system grew from 11.5 quadrillion Btu (qBtu) to 14.1 qBtu (British thermal unit—a standard measure of thermal (heat) energy). This 2.6-qBtu increase accounted for over 80 percent of the rise in total U.S. energy use between 1997 and 2002.

Three factors were responsible for the jump in food-related energy use:

Population growth accounted for 25 percent of the higher food-related energy use in 2002 versus 1997. The U.S. population grew by more than 14 million (5.1 percent) over the 5-year period. More mouths to feed means increased production of food and food-related items, ranging from fertilizers to frying pans, pushing energy used by the food system up by 0.64 qBtu.

Higher food expenditures also boosted U.S. food system energy use by 25 percent. The amount of food marketed to U.S. consumers, measured in real (adjusted for inflation) dollars, increased 6.6 percent per capita between 1997 and 2002, according to BEA data.  In 2002, the mix of commodities marketed to U.S. consumers included a greater proportion (in real dollar terms) of foods that used less energy, such as fresh produce and fish, and a smaller proportion of more energy-intensive commodities, like processed fruit and vegetables, pork, and beef.  This changing mix, however, was accompanied by the substantial increase in food marketed per capita to U.S. consumers, resulting in a net increase in total food-system energy use of 0.65 qBtu.

The use of more energy-intensive technologies accounted for about half of the 1997-2002 food-related energy increase. Businesses and households look for efficiency gains, so the relative costs and substitutability of energy and labor are major determinants of the amount of energy used by the U.S. food system. Between 1997 and 2002, businesses faced increasing labor costs, while energy prices were lower and far less volatile than they have been since 2002. A shift from human labor to energy-using equipment occurred for all food and food-related commodity groups, except pork.

The egg industry illustrates the long-term trend of substituting energy-intensive technology for labor. High-technology, energy-intensive hen houses, and more use of liquid, frozen, and dried egg products (instead of whole eggs) increased energy use per egg by 40 percent in 1997-2002. Processed egg products are widely used by the foodservice industry and by processors as ingredients in other foods, such as mayonnaise and baked goods.

The story is much the same in kitchens across the country. Consumers are relying on blenders and food processors instead of knives and chopping blocks, and self-cleaning ovens have replaced EASY-OFF and elbow grease. Modern appliances, while sometimes more energy efficient, still require energy to manufacture and operate. ERS estimates that food-related home energy use increased by 3.9 percent per meal between 1997 and 2002.