With the idea that medical science has brought us so far, and i am about to mix fact with fantasy and a kitten might die some where because of it i would like to say this:
You COULD treat the Zombie-ism as almost like a Vampirism.
In the sense that when one first has contracted the Zombie virus, they are still mostly human, maybe with a few little resistances added on or maybe a natural armor bonus because their skins hardening, what have you. Eating Corpsuse sustains the hunger and they are allowed to live their "life" as "normal", but if they dont feed, the virus spreads...
This comes from the fact that when people first die the body dosent decompose instantly, and in all fact, the body still functions for a few hours after "death" ( of course this does depend on the death in question, bullet to the brain, yeah, having a 300K metal beam fall on you, not so much)
So, in theory, if you "replenish" the blood and dying tissue with "fresh" tissue, you would stay at the state you were when you "died". This is like the theory behind Vampires, they're dead and they need fresh blood to keep their bodies functioning.(old mythological idea there) The Zombie Virus could act the same way, either provide more fresh flesh for it to consume or its going to consume yours.
This could have Pros and cons depending on how you go about it.
On the one hand if you cant find any food for a while for what ever reason ( maybe you in prison or trapped in a cave) you get the properties of the undead, and getting a lot of advantages for it, like being immune to certain attacks or abilities.
On the other hand, because your body has decomposed so much, you have to consume X amount of bodies now to get back to your normal state, and you cant really tell who's friend or foe anymore, and might require a WILL save in order to not eat them( you are so far gone at this point every thing looks tasty, like a stereotypical zombie) but you have JUST enough intelligence left to be able to think... even if its at about the same level as a dog or house cat.
... Too much?