It's always going to have *some* effect but the severity of the "offense" and what kind of damage control you do will determine how much backlash you get. If it's only once in along while and you pick up where you left off (with diet and exercise) right away, then the damage should be negligible. Remember that there is about 3,500 calories in a pound of fat, so that's how much excess you have to eat in order to gain just one pound of fat back. Just remember how quickly that stuff adds up. And how hard it is to get it back off.