It's a matter of greed, really. "Oh just one more-- just one more-- just one more--" leads to obesity just because they don't know when to put the burger down.
GLUTTONY is the overbearing want for food or even as far as hording things to a mass extent. Usually food though. Greed is the want and hording of material wealth. I'm greedy, but I'm sure as hell not fat. Why not? Fast food's to expensive, I won't be wasting my money on that! PFFT.
Meh. You know what I meant. It's the same concept.