The scripture tells us that the blood of Able cried out to God from the ground. St. Paul in Hebrews 12:24 tells us that the Blood of Jesus speaks better than the blood of Able. Following this same line, St. Gregroy Palamas says that when we fast the members of our body suffer and this very suffering is prayer: prayer that is added to our prayer. That is, fasting increases our prayer because our weak and suffering body is also crying out to God with our mind.
So when you hear the tummy growl or feel a little pinch of hunger, understand that it is the feeling of your body praying. Your body is praying with you, adding to your prayers, like the blood of Able crying out to God.