Depending on your own lifestyle and health, when you hear the word "carbohydrate," you might immediately think of a diet limiting your favorite high-carb foods. You may also think about limiting carbs to control diabetes. Carbs are actually an essential nutrient that creates a form of energy called glucose, which Harvard School of Public Health describes as "a universal energy source."

Primary Function

The primary function of carbs is to supply energy to the body. Carbs in combination with proteins, fats, vitamins and minerals make up the essential nutritional components needed for life. While carbs provide adequate caloric value to maintain the body's vital functions and are the body's preferred source of energy, they cannot supply all of the nourishment needed to maintain adequate health for an extended period of time.

Digestion

Once a carb has been consumed, it immediately enters the digestive process in the mouth. Once the carb has been chewed, it enters the stomach, where it is broken down into smaller parts, which are forms of sugar. This sugar is absorbed into the small intestine and transported to the bloodstream. After glucose enters the bloodstream, it is transported throughout the body to various organs to be used for energy. In addition to the body's organs, muscles and the brain benefit from the energy provided by glucose, also known as blood sugar.

Weight Gain

The body does not always need all of the energy provided by the glucose in the bloodstream. Extra glucose is then taken to the liver and skeletal muscles for storage in the form of glycogen, which is ready for use when the body's energy needs exceed the amount of glucose available. The body can only store a limited amount of glycogen, so any extra glucose is stored in the body as fat. This extra fat leads to weight gain.

Protein as Fuel

Protein is an essential nutrient. Its primary role is the development of tissue and muscle. Protein is available as a source of energy when carb intake is not adequate. When carbs are not readily available for energy, protein is broken down for energy. This breakdown can put added stress on the kidneys, with protein byproducts being excreted in urine. According to Iowa State University, "Carbohydrate spares the use of protein as an energy source."

Brain Function

The brain and central nervous system rely on glucose for their primary source of energy. Without adequate carb intake and glucose levels, you might begin to feel tired, dizzy and weak. Athletes need adequate amounts of carbs prior to a competition for optimal physical and mental results.

Fiber Source

Indigestible carbs exist as dietary fiber. The body needs fiber for two primary functions. Insoluble fiber is needed to increase the bulk of the stool and assist in regularity of bowel movements. Whole wheat bread, grains, fruits and vegetables are good sources of insoluble fiber. Soluble fiber -- found in oats, beans and barley -- is believed to help lower cholesterol and decrease glucose levels.