Why Does a Body Need Glycogen?

Glycogen is the body's stored energy, with the biggest storage site in the liver and the balance in the muscles. For normal movement and brain functioning in a healthy and well-nourished body, energy is pulled first from the glucose contained in the bloodstream. Once that is depleted the body pulls its needed energy, in the form of glycogen, from its storage sites.

Features

• 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. When you begin to workout the body uses it glycogen stores, but the body is smart. It knows it cannot fully deplete its glycogen stores or it will have nothing to use for quick energy (imagine not being able to walk or run because your body has no energy to move).
  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.

Function

• 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. Anorexics are in danger of this. The cardiac muscle is very rich in glycogen and for daily functioning receives approximately 25 percent of its fuel from glucose. Without the consumption of enough glucose-containing foods, the heart will suffer. For this reason, many anorexics and bulimics damage their heart.

Considerations

• If the body has too much glucose and all its glycogen storage sites are full, it begin to convert glucose to fat. It is, therefore, very important to watch your diet carefully and not to over consume sugary foods and foods whose carbohydrates can be converted to glucose. Once excess sugar is stored as fat, it will take much longer to burn it off, as the formula below will demonstrate.

Misconceptions

• After about 20 minutes of exercise, your body switches to fat for its energy source. Hence, in order to begin to burn fat off in your workout, you must work out for at least 20 minutes. At this interval, about 20 percent of your energy begins to come from fat. As the liver stores approximately 4 hours of glycogen before significant fat is used for fuel (about 95 percent), you would need 4 hours of almost constant activity before your body would switch to fat as its almost exclusive source of energy. People in jobs that require constant movement are fortunate that their bodies have trained themselves to turn to fat sooner than a "weekend warrior" who is locked into the above formula.

Expert Insight

• 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.