This is the correct answer. There's no such thing as conservation of mass, mass and energy are convertible into each other. But in the real of chemistry that c

This is the correct answer. There's no such thing as conservation of mass, mass and energy are convertible into each other. But in the real of chemistry that conversion happens on a ratio of at most 1e-7, so when it comes to the human body we might as well say that the weight that goes in must equal what comes out, and that's close enough.