When your body needs energy, it can use glycogen reserves. The glucose molecules in the food you eat are mainly stored in the liver and muscles. From these reserves, your body can quickly mobilize glycogen when it needs fuel.

What you eat, how often you eat, and your activity level all affect how the body stores and uses glycogen. Low-carb and ketogenic diets, as well as intense exercise, deplete glycogen stores, forcing the body to burn fat for energy.