Starch, as in white flour, is not too bad, since it depolymerizes into glucose which is readily used by the body or converted to fat.
Sucrose (cane sugar) is bad, because it is a disaccharide that consists of one molecule of glucose and one molecule of fructose, i.e. it is 50% fructose. The fructose has to be metabolized in the liver, sort of like ethanol.
Glucose is exactly what becomes “blood sugar.”
That is exactly what diabetics are having a direct problem with, each day, and the only thing insulin tries to work against.