one big energy usage is maintaining a resting membrane potential of 70 mV across the cell membrane. All cells in the body have a sodium/potassium pump that moves a single positive ion up the gradient across the cell membrane for each cycle of the molecular pump.

each pump moves about 100 ions per second. How much energy does it take to move that many ions up the cells membrane potential in (eV)

on average each cell in the body expresses about 4 million pumps similar to this, and the average body has about 10 trillion cells. How much power (watts) does it take to run all these pumps

connecting to food, use that power that we found about to find how many kilocalories of energy this corresponds to in a single day