Well, if you are doing WW, try not to go under your daily points. Flex points are up to you. Once and while is no big deal. But you can actually stop losing or even have a gain if you don't get enough points. Think of your metabolism like a fire, if you don't give it fuel(wood), it's going to stop burning eventually. The more you eat while losing, the more you can eat while maintaining. You have to eat to keep your metabolism burning. Good luck!