my stomach lets me know in quite a noisy fashion when its time to eat.
Also i agree with jayell about the apple
i often have to ask myself, am i really hungry, or am i just trying to convince myself (and my fiance) that i am, so i have an excuse to eat fast food.
often times i will tell my fiance im hungry, and he will say "there is food in the kitchen"
and ill tell him i dont want to cook, or there isnt anything to eat or blah blah blah *insert some believable excuse here*
Thats when i know im not hungry and i just want to eat crap i shouldnt eat lol