The major role of carbohydrates in the human diet is to provide the body with energy. The body can also store it to provide fuel, especially for high-intensity exercise.
Glucose travels through the bloodstream to fuel the contractions of the muscles. Glucose also powers biological processes like digestion, metabolic reactions, and glandular secretion.
Glycogen: The Body’s Main Storage of Glucose
After eating a meal, the carbohydrates are broken down into monosaccharides (single sugars). Some of the glucose is transported to the bloodstream. The other sugars travel to the liver for further processing.
The liver metabolizes much of the fructose and galactose for energy. What happens to the other sugars depends on the body’s energy needs.
The glucose is transported in the blood to reach the various tissues of the body. The glucose is regulated to only about 70-100 mg per 100ml of blood.
The brain cells and the blood cells rely on glucose as a primary energy source. Hence, an adequate amount of glucose is important for brain and blood function.
If blood glucose rises above normal, the pancreas secretes insulin. This hormone causes the liver cells to condense the excess glucose into a storage form called glycogen.
When the glucose levels fall below normal, the liver cells breakdown the glycogen and release the glucose into the bloodstream. The glucose becomes available to supply the brain and body tissues with energy.
Skeletal muscle cells also store excess glucose as glycogen. However, the muscles only store it for themselves and use it during exercise and other physical activities.
Glycogen holds water and is bulky. Hence, the body only stores enough of it to last for a short time. You can use it up in approximately two hours of continuous exercise or 18-24 hours when the body is at rest.
When you use all your glycogen stores, your body turns to its long-term water-free fuel source: fat. During prolonged fasting or starvation, the body starts to metabolize fat for energy because of the absence of glucose.
What Happens When Carbohydrates Are Depleted?
Several body tissues, like red blood cells, only use glucose for energy. Certain parts of the brain and the central nervous system also rely primarily on glucose to function. What happens when there is none?
During the absence of glucose, the liver starts to partially breakdown fat into ketone bodies to supply the brain and other tissues with energy. This process is called ketogenesis.
The muscle cells can also rely on fat for energy. However, if you overexercise or undergo prolonged starvation, your proteins will become a source of fuel as well.
The liver and the skeletal muscles store just enough glycogen to provide energy for a few hours. To keep providing the body with enough glucose for fuel, you need to consume dietary carbohydrates frequently.
If you fail to supply your body with sufficient carbohydrates in your diet, your body will draw energy from fat and protein. If you want to spare your protein from being used as energy, you have to eat enough carbohydrates.
During prolonged starvation, the proteins from the muscles and vital organs will continue to withdraw. This withdrawal, if continued, will result in weakness and poor bodily function.
The major role of carbohydrates in the human diet is to provide energy. Glucose is a crucial fuel source for the brain, red blood cells, and other tissues of the body. Hence, you have to eat sufficient amounts of this macronutrient, especially if you want to engage in rigorous exercises and other physically-demanding activities.