Glycogen is the body’s stored energy, with the biggest storage site in the liver and the balance in the muscles. When broken down in the body, glycogen is transformed into glucose. A great deal of research has been done on glycogen and its role in the body ever since it was recognized as a critical part of the body’s energy storage system.
Glycogen is stored glucose. After eating, the body takes the glucose it needs to function for movement and brain power and stores the rest as glycogen in the liver and muscles, to be used at a time when it is needed. This is called glycogenesis. In humans, the body can store around 2,000 kilocalories of glycogen at any given time. When people eat, levels are refreshed, with the body working to keep levels as stable as possible so that there is a steady supply of energy.
After a few hours without refueling by food consumption, the body’s glycogen stores are exhausted and yet the nervous system continues to demand it. Lower glycogen stores result in sluggish mental and physical reactions, making it difficult to concentrate and respond to emergencies.
When blood sugar goes down, glucagon (a hormone) is secreted which turns glycogen into a fuel source (blood sugar), called glycogenolysis. When muscles contract, glycogen is broken down into glucose and the glucose is used as energy. After exercise, the body will replace its glycogen stores as soon as you eat something. If glycogen and fat reserves are depleted, the body begins to break down protein and use it as a fuel source.
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.
Twenty-five percent of the body’s glycogen is stored in the liver, with 75 percent in the skeletal muscles and trace amounts in the heart and other tissues. Care must be taken not to undereat the foods needed in order to synthesize glycogen in the body and also not to overeat sugary food, as excess glycogen and glucose will be stored as fat. Balancing out complex carbohydrates that have a low glycemic index to simple carbohydrates is an important consideration when planning meals.
If you begin to get the mid-afternoon slumps, try eating a piece of cheese, a few grapes and whole wheat crackers. The fiber will be good for you and the fruit will give you that little bit of a glucose boost that you need.