If you're fasting, you can't eat. But you still need to hit your macronutrients. The good news is that it's pretty easy. When people say, "you can eat whatever you want," they're only partially right. You can eat whatever you want… as long as it fits within your macros. Macros are protein, carbs, and fat. They're the three things your body needs in order to function properly, and they're not created equal. Different foods provide different amounts of each macro in varying combinations; for example, chicken breast has more protein than fat or carbs, whereas brown rice has a lot more carbs than protein or fat.