Don't beat yourself up about a dessert! It takes a lot of calories—3,500—to gain a pound of body fat. A one day treat doesn't usually result in any significant weight gain, it’s what you do the next day and the day after that's really important—so don't stay off-track. So be sure to whittle away at those extra calories over the next day or two, preferably by boosting exercise rather than eating too little. Starvation is not the healthy answer!