Why am I not Fat?

I don't eat all that healthy. And I eat a lot. I was just getting done with my breakfast the other day. (2 doughnuts, 3 mini-muffins, a cup of yogurt, and an ensure breakfast shake) I was putting the some stuff away, and I happened to look down at the nutrition label for the mini-muffins. I saw that each muffin had 100 calories, 26 carbs, and a couple of grams of protien. These things are small, they are litterally bite size. I was stuned. So I looked up the rest of the nutrition facts for that meal. All in all, there were about 1200 calories, 400 carbs, and like 40 grams of protien.

That's insane. There are some people that don't get that in a day, and I ate it in a single meal. Now that meal was a little on the high side of things, but it's not to far from what I get in nutrition in every meal. I just don't understand why I can't gain weight. Yeah I understand I have a high metabolism, and yeah I exercise, but that's just rediculous. But man it tastes good!!!