The human body has an efficient and complex system of storing and preserving energy. Glucose is a type of sugar that the body uses for energy. Glucose is the product of breaking down carbohydrates into their simplest form. Carbohydrates should make up approximately 45 to 65 percent of your daily caloric intake, according to MayoClinic.com.
Food Sources of Glucose
Glucose is a simple sugar found in carbohydrates. When more complex carbohydrates such as polysaccharides and disaccharides are broken down in the stomach, they break down into the monosaccharide glucose. Carbohydrates serve as the primary energy source for working muscles, help brain and nervous system functioning and help the body use fat more efficiently.
Function of Glucose
Once carbohydrates are absorbed from food, they are carried to the liver for processing. In the liver, fructose and galactose, the other forms of sugar, are converted into glucose. Some glucose gets sent to the bloodstream while the rest is stored for later energy use.
Once glucose is inside the liver, glucose is phosphorylated into glucose-6-phosphate, or G6P. G6P is further metabolized into triglycerides, fatty acids, glycogen or energy. Glycogen is the form in which the body stores glucose. The liver can only store about 100 g of glucose in the form of glycogen. The muscles also store glycogen. Muscles can store approximately 500 g of glycogen. Because of the limited storage areas, any carbohydrates that are consumed beyond the storage capacity are converted to and stored as fat. There is practically no limit on how many calories the body can store as fat.
The glucose stored in the liver serves as a buffer for blood glucose levels. Therefore, if the blood glucose levels start to get low because you have not consumed food for a period of time, the liver is able to release glucose into the bloodstream to maintain healthy levels. Blood glucose levels are tightly regulated because glucose is the primary energy source for the central nervous system. Blood glucose also is important for sustaining brain functioning. If the body reserves of glucose deplete, a process called gluconeogenesis will take place. During gluconeogenesis, glucose is synthesized from molecules that are not carbohydrates. Often, this means the body will break down muscle fibers to obtain the molecules to produce glucose.
Muscle glycogen reserves are stored energy for the muscles. The glycogen is able to be broken back down into glucose when the muscle contracts and requires energy. The body is able to store 500 g of glycogen, roughly equivalent to 2,000 calories, in the muscles. Therefore, if you did not eat for a day, you will have drastically depleted these stores. After an intense workout, when these glycogen stores have been tapped into, consuming carbohydrates will replenish these reserves.
- "Pocket Atlas of Nutrition"; Hans Konrad Biesalski, Peter Grimm; 2005
- Mayo Clinic: Healthy Diet: End the Guesswork