Glutton zombie courtesy Return of the Living Dead

It may seem hard to believe now, but zombies didn't always eat brains.  In fact, they didn't eat anything.  First they were dead and then they were alive and that was that. Ah, the simpler times...

"It was wrong of you to lock me up. I had to hurt myself to get out. And I know you're in here, because I can smell your brains." -- Freddy, Return of the Living Dead (1985)

But nowadays, these newfangled zombies want more.  It's not enough to just moan and shamble along.  Gluttony zombies are hungry.  All the time.

Gluttony, from the Latin word gluttire ("to gulp") has been on the rise in the world of sin, if only because the citizens of industrialized countries are no longer running for their lives from lions and tigers and bears. Instead, they're sitting on the couch eating cream-cheesed slathered Twinkies while watching the latest reality show. This is especially true in America, where people are getting fatter by the second.

The trend of the gluttonous becoming glutton zombies might lead one to believe that all glutton zombies are big fat guys.  This isn't necessarily true.  Gluttony is a tricky sin; it's not just the consumption of food, it's the overconsumption of anything to the point of waste. So there are most certainly skinny, rich gluttony zombies and thin gluttony zombies who never recycled.

Point being that where they overconsumed in life, glutton zombies can never get enough in death. Sloth zombies may wander around in a daze, but glutton zombies are perpetually driven by an all-consuming hunger that can never be satiated.  Their stomachs have long since stopped working, so they're just going through the motions, chewing on the brains of others.

It begs the question: why brains?  Not all glutton zombies are necessarily after brains -- some are more properly ghouls, intent on just consuming their prey. One theory is that the zombies who hunger for brains are actually trying to regain a tiny bit of the thought process that led to their demise; others postulate it helps ease the hunger.  There's even the theory that zombie hunger is so unbearable they instinctively want to stop others from experiencing it, and the quickest way to do that is to go for the brain. 

But eating a person's stomach might make a lot more sense.