It gets 'deconstructed', the body keeps any bits that are useful (minerals, various wanted compounds, etc), any rubbish (excess usable/unusable compounds, exces

It gets 'deconstructed', the body keeps any bits that are useful (minerals, various wanted compounds, etc), any rubbish (excess usable/unusable compounds, excess minerals) gets disposed of, the rest gets burned for energy and finally gets to release CO2 and water vapor into the atmosphere. Think of a building being demolished. A lot of the material can be reused, a lot of it thrown away, and some of it sold to recoup some costs.