Sparing Protein
In a condition where there is not sufficient glucose to meet the requirement of the body, glucose does the process of synthesis from amino acids. Because there is no amino acid storage molecule, this procedure needs the destruction of proteins, significantly from muscle tissue. The presence of enough glucose spares the breakdown of proteins from using to make glucose required by the body.
https://www.healthline.com/nutrition/carbohydrate-functions#TOC_TITLE_HDR_5