Breakfast is Probably the most necessary meal off the whole day. After 6 to 10 hours of fasting that’s what exactly it’s name says. It is supposed to break the fast. Your body moves on energy. This energy comes from glucose. Without glucose your body will start trying to find it and will use up any energy it had from the previous meals to do exactly this. So what you will feel is that your brain cannot focus, you will feel tired and even sleeping. This is because he is saving the reserve has until it finds new glucose. Same with the muscles are muscles are designed to move with the glucose. If they don’t have glucose you will feel like you don’t even wanna get out of bed or get up from your chair and again it will start entering a state of sleepiness until it finds the glucose it needs. Now if you actually fill this need with very sugary high carb food You are now going to spike up the glucose and when it drops you will feel go back to feeling sleepy again, like a roller coaster.