Preserve Muscle
Glycogen storage is one of the various ways your body ensures it has sufficient glucose for all of its working. When glucose from carbohydrates is not sufficient, the muscle can also be broken down into amino acids and then converts into glucose or other substances to make energy. This isn’t an ideal situation, since muscle cells are critical for body movement. Extreme losses of muscle mass are associated with poor health and the risk of death also increases.
https://www.everydayhealth.com/carbohydrates/guide/
https://www.reidhealth.org/blog/carbohydrates-101-the-benefits-of-carbohydrates