When you're sleep deprived, you reach for doughnuts and pizza. A new study has figured out why you crave more calorie-dense, high-fat foods after a sleepless night. Blame it on your sleepy nose -- or olfactory system. First, it goes into hyperdrive, sharpening the food odors for the brain. But then there is a breakdown in communication with brain areas that receive food signals. Then decisions about what to eat change.

Source: Why we crave junk food after a sleepless night