What is Glycogen?
The body cannot store carbohydrates/ sugar. It is converted by the liver and stored as glycogen. The liver produces glycogen from carbohydrates you eat. That is the simple explanation. But the liver will ONLY produce glycogen IF your storage has been depleted or is empty. The rest of the carbs you have just eaten will be stored as fat (triglycerides).
In your daily life of constant eating - breakfast, lunch and dinner as well as a number of snacks a day, simply because the bag of crisps is at hand - you will use some of the "food" as instant energy (as long as you are not insulin resistant), the rest will be stored. That's why we have an obesity epidemic today.
How much glycogen can be stored?
It is very different depending on the person. But let's take an average person weighing 70Kg. The liver can store approx 100-120 grams of glycogen. This can be accessed easily in order to give you needed energy. The skeletal muscles can store a bit more approx 400 grams of glycogen. However once you have depleted the glycogen stored in your liver, what is stored in the liver CANNOT be accessed by the body, only your muscles.
So if you don't move around a lot your body is crying out for energy and tells you to eat ASAP. If that meal takes a long time, and your body is desperate for energy it needs a quick fix, the body will initially use your muscles and convert them into glucose. When you sleep at night (and activity is low) and your body runs out of energy in the liver, it will actually use fatty acids/ triglycerides as energy and covert them into ketones. Yes you are in ketosis almost every night, depending on how much you had to eat before bed. As soon as you have your bread/ cereal and orange juice you revert back to living of carbohydrates.
This is a roller coaster and you will often experience hunger, brain fog and you can easily become lethargic.
This is TOTALLY AVOIDED on a Ketogen Diet where you will NEVER run out of energy.