The answer is Glycogenolysis
When we are hungry or skipped a meal our glucagon, an hormones that regulates blood-sugar levels, is released to avoid glucose levels in the blood to decrease to a risky value.
Glucagon makes the liver, but also the muscle, to breakdown accumulated glucose called glycogen into glucose to increase blood-sugar levels. This process is called Glycogenolysis and can also be stimulated by an increase in epinephrine during fight-or-flight responses.
