You know chocolate has caffeine, but you may be surprised to hear that some of the darker bars can have as much as 80 milligrams—the amount in a can of Red Bull. As a general rule, the darker the chocolate, the stronger the stimulant.
A better sleep snack: Save the chocolate for breakfast (Really! Research shows it can help you maintain a healthy weight), and at night, snack on trail mix with walnuts, almonds and dried tart cherries. All three are good food sources of melatonin, a hormone that promotes a more restful sleep.