Glycogen is a form of glucose, a main source of energy that your body stores primarily in your liver and muscles. Your body needs carbohydrates from the food you eat to form glucose and glycogen.

What is glycogen?
Glycogen is the stored form of glucose that’s made up of many connected glucose molecules. Glucose (sugar) is your body’s main source of energy. It comes from carbohydrates (a macronutrient) in certain foods and fluids you consume. When your body doesn’t immediately need glucose from the food you eat for energy, it stores glucose primarily in your muscles and liver as glycogen for later use. Your body creates glycogen from glucose through a process called glycogenesis. Your body breaks down glycogen for use through a process called glycogenolysis. Several different enzymes are responsible for these two processes. An enzyme is a type of protein in a cell that acts as a catalyst and allows certain bodily processes to happen. There are thousands of enzymes throughout your body that have important functions.

What’s the difference between glycogen, glucose and glucagon?
Glycogen, glucose and glucagon are all related to how your body uses its main source of energy from carbohydrates, but they all have different functions. You get glucose from carbohydrates in the food you eat. Blood glucose (blood sugar) is the main sugar found in your blood. This sugar is an important source of energy and provides nutrients to your body’s organs, muscles and nervous system. Glucose is very important because it’s the primary source of energy for your brain. In fact, your brain’s constant requirement for glucose is the primary reason why the current recommended dietary allowance (RDA) for carbohydrates for all adults is at least 130 grams per day.
When your body doesn’t need glucose right away, it stores it as what is glycogen in your liver and muscles. Glucagon is a hormone your pancreas makes that triggers glycogen to convert back into glucose and to enter your bloodstream so your body can use it for energy. Glucagon and insulin are the primary natural hormones that regulate your body’s blood glucose levels.

Where is glycogen stored?
Your body mainly stores glycogen in your liver and skeletal muscles (the muscles attached to your bones and tendons), with small amounts in your brain. Although your liver stores a greater ratio of what is glycogen than your skeletal muscle, since your total muscle mass is greater than that of your liver, about three-quarters of your body’s total glycogen is in your muscles. During intense and prolonged exercise, the glycogen in your active muscle cells can substantially reduce.