What Is Glycogen?

Glycogen Structure

The principle form of carbohydrate energy (glucose) stored within the body’s liver, muscle and fat cells.

Glycogen is the main way the body stores glucose for later use. It is a large molecule produced in the liver, although it is also stored in the muscle and fat cells. After carbohydrate ingestion, more glycogen will be produced, and then released as blood glucose levels fall. Low-carb diets initially deplete glycogen storage, although to some extent any weight loss diet has the same effect. Since glycogen molecules have quite a bit of water attached, some “water weight” is lost at the beginning of any weight loss diet. The glycogen stores are partially replaced subsequently.

Athletes can experience a situation in which their glycogen reserves are depleted. This occurs in endurance activities, in which the body slowly uses up its supplies over the course of an event like a marathon. When this point is reached, it is sometimes referred to as “hitting the wall,” thanks to the strain it puts on the body. The athlete's size and condition have an effect on when she or he will hit the wall. Athletes attempt to avoid this by carb loading before events, and they also eat quickly after events to rebuild their reserves.