Why does Marijuana suppress my appetite?

Everyone knows MJ is supposed to stimulate the appetite (i.e. the munchies) which is something i experience when i'm actually stoned. However, when i'm not stoned, by the time lunch and dinner come around, i'm not the least bit hungry or interested in eating. I generally just smoke before i go to bed, so 80% of the daylight hours when i'm awake and not high - eating is uninteresting.