The role of insulin i sto allow the entrance of glucose into cells where will be burned to the energy which is absolutely necessari to survive.  However we have already seen that in the diabetic individual insulin is absolutely absent (type 1 diabetes) or partially absent and or not working (type 2 diabets) and  thus the glucose is left outside the cells: because of this we can realize that diabetes is a “glucose deficient state” or at least a a disease characterized by maldistribution of glucose since this substance builds up outside the cell to create damage, but does not enter the cell that is left in a state of poor nutrition. 
 A consequence of this is that the body cannot utilize the glucose and utilizes the proteins instead, and this contributes to the chronic fatigue of the uncompensated diabetes.