My first comment: maybe this thread should have a discussion of what is or is not a "Fast".  Personally, I would not consider what you are doing as a "fast". However, if you take a looser definition, a fast is anytime you don't eat.  So, I guess if you go 4 hours without eating, that is a "Fast" However, I think most individuals would say more like 16 hours - or longer - without food to have a Fast that is consequential.

My second comment: I wonder if the potatoes in your diet are undoing what you are trying to achieve.  Think about taking them out and substituting another food item. 

My thoughts. And I am by no means an "expert" in this subject.