system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that if I'm hungry right before going to bed, I'm not longer hungry when I wake up in the morning?

The other night, I was going to bed and felt pretty hungry, but I just went to bed. I woke up, expecting to be somewhat hungry but the feeling of hunger was gone. Does anyone have a nice quick explanation?
gpt
Very concise answer: The loss of hunger when you wake up is due to excess glucose in your system caused by the breakdown of glycogen from your liver while you're asleep.

Explanation: Glucose is the main source of energy that your cells use to generate ATP, which powers many processes in the cell. When you eat, the glucose in your food, in the form of sugar and carbs, is absorbed into your system and spread to your tissues. Any excess glucose that you eat is stored in the cells in your liver in these giant chains called glycogen. These glycogen chains serve as a way to save the excess glucose for when your body needs it, much like how you store excess fats and lipids in your fat cells.

The prime example of when the body needs these stores is when you're asleep. Think about it. The average person sleeps for 7-8 hours. For that same amount of time during the day, you can easily fit in two full meals, so your body needs some way to keep all of your organs supplied with glucose when you have no ability to get it from food yourself. That's when these glycogen molecules come into play. As your body falls asleep, the liver starts breaking down these long chains of glucose and releasing the individual glucose molecules into your system. This makes sure that all of your organs (especially your brain) is supplied with glucose throughout the entire night. This breakdown occurs for the entire time you're asleep and stops when you wake up (and shifts back into storage mode). But right when you wake up, the glucose in your blood is still high from the overnight glycogen breakdown process, and there still may be some residual breaking down as your body shifts back into an awake state. The higher level of glucose in your system tells your brain that "you're full' even though you may have not eaten anything for 12 hours by that point.

You may have noticed that you got REALLY hungry within a couple hours after waking up. That's your body realizing that you haven't eaten anything in 12 hours AND you have the ability to do something about it.