Turn your cheat day around Feeling guilty about that giant ice cream sundae you enjoyed at your nieces birthday party? Dont beat yourself up! It takes a lot of calories—3,500—to gain a pound of body fat. "So really, that one off day doesnt usually result in any significant weight gain," says Newgent. Its about what you do the next day and the day after thats really important—so dont 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!