"If you stop being hungry for too long, you stop being able to tolerate it," he explains. It's one reason. It used to be very nearly the reason. "Being really satiated can be hard to come down from. I like not having to think from here all the time." He points to his stomach--which isn't what he means, but it will do for a metaphor.
"Besides," he adds sniffily, "mazoku who let themselves be gluttons end up with no table manners, ne." Stupid creatures, eating everyone in sight with blood all over the walls and no one to entertain them from one week to the next, never able to feed off the same village twice in a decade, getting exorcised and mobbed with pitchforks all the time. Bo-ring.