Are you referring to the energy in chemicals expelled from the body? Once through the digestive system (absorbed in the intestine) there are actually remarkably few ways for chemicals to exit the body. The main route is through respiration, through which CO2 is released. Urine expels liquid-soluble wastes. The energy contained in these wastes (that is, the free energy available from reacting with oxygen) is very low, so it's usually ignored. There are other minor routes (such as sweat and milk), which, aside from special circumstances (lactation) don't expel much energy either.