What is the primary fuel for the body?

carbohydrates

lipids

protein

glycogen

It's the glycogen.

Glycogen is a complex molecule made from glucose, it's a ramification of about 12 to 18 molecules of glucose, and it's the metabolic energy reserve.

When we need energy, the first to get metabolized is glycogen.

You can find most of the glycogen in the liver and a bit in muscles.