As stated in Chapter 603, Zetsu tease him that they were no need to;
eat food, no need to go toilet or poo.
So, now Obito - half human, half parasite?
Interesting....
Well the Zetsu are said to be artificial humans though sometimes they get the parasite aspect, dunno what they´d leech from when not from the statue. Let´s just say half-real and half-artificial