Depends on the person, their genetic disposition so I don't think it's a question that has a comprehensive answer to. Each to his own, breakfast means to break the fast which has occurred during eating and drinking nowt whilst asleep. If it suits you to eat then do so and think about how you spend your morning as to whether it's going to burn off the calories or not. Go with the flow is my opinion, just eat as healthily as you can 'no kerapp' food and let nature take its course.