Here's the thing, technacally zombies do not need to feed/eat period, they are essentally immortal, and usually won't die of natural causes. The reason zombies feed is because in the lore the zombie virus generally strips down their intelligence to their base instincts, and one of those is to feed, its also how the virus spreads itself. Zombies don't actually have any need of food or water. Thats the usual zombie lore in general. Virus/infection basically strips their mind of everything but the need to feed.