Hello ouka,
It is excreted in sweat, and defication. It is also lost in other ways as well. Remember the mass is essentially broken into much smaller peices that can be lost in all sorts of ways when it is 'burned' for energy. This means that the energy is transfered as heat out of the system and your left with lots of smaller more managable pieces. The mass isn't just globbs that have to leave the system.
I hope this was at least a bit helpful,
sorry for the delay