You're the boss: no one can stop you from having a piece of birthday cake or a slice of pizza if you choose to enjoy, celebrate, or take a break. One meal - or even one day of meals - won't make or break your overall success. On the other hand, if your "cheat day" turns into a "cheat week" , or if you're having "cheat days" on the regular, you probably won't see the kind of results that you were hoping for when you started following a low carb diet. If you're having a hard time sticking to a low carb diet, it might be a sign that you need to try a different approach too.