Your body is beyond clever—that we knew—but ever wondered how it knows when you’re full? How it knows not to eat all the double-stuffed oreos? The little worker in charge of all that hunger-regulation: leptin. A protein secreted by stored fat, leptin is a hormone that tells your body you’ve had enough and triggers your metabolism. Interestingly, it causes decreased appetites in rats, but in humans it only causes weight loss and hunger control to a point—a surge of pleasure chemicals (hello, oreos) can overrule leptin’s powers at times. The bottom line: When you start to feel like you’re full, but you keep eating anyway because you, love, your, dessert? Unfortunately, that one’s on you.

GALLERY: Outsmart Your Eating Instincts