When your body needs something it is represented by hunger or craving. For example in female pregnancy "cravings" alot of times are the body saying you need something. Your sodium might be low if you are craving salty things or potassium if you want bananas etc. When you are eating more often and that hunger comes on really strong and quickly like it should be after you have a heavy workout. That's when I no longer have to plan eating every few hours it has become natural. There are metobolic tests available through specialists but if you just learn to listen to your body and control cravings for sweets and bad stuff you will do fine.