If food isn't available, I can have a very small appetite. I can go days with eating just a loaf of bread and a few thin slices of cheese.
But when there's food, I eat a lot, because I consume a lot of energy during the day. I can take out a large box of pizza during lunchtime, and then devour another large box at supper because the previous energy that I took in is already gone - for reasons that can't be explained. I tend to eat fast so the 'full stomach' effect won't get on me before I finish a meal. I used to eat much less as a little kid, but people keep saying that I'm getting skinnier as I'm growing older, despite the fact that I keep eating more and more. I usually skip breakfast & lunch, though.
My appetite isn't the largest of all, I'm sure of that.