According to a life cycle analysis of the u. s. food system conducted by the university of michigan, the u. s. consumes 13.9 quads of mostly fossil fuel energy to produce 1.75 quads of food energy annually. a quad is a unit of energy equal to 1 quadrillion (1015) british thermal units (btus). one quad is equal to the energy of 183 million barrels of petroleum. here is how energy consumption breaks down by component in the u. s. food system: