Food And Protocols

Can you clarify how much we are meant to eat when doing a fasting protocol. One video said do not restrict calories or under eating and eat a the same amount of food just in the smaller eating window but if you say skip breakfast and ‘eat in’ you are getting that ‘food’ off your body, then why do you need to eat it later in the eating window? I know we aren’t meant to focus on calories but if you did only eat the two remaining meals (if you did skip breakfast for example) you would be under eating?