When a carbohydrate is high on the glycaemic index, it refers to the speed and quantity with which it is digested and transported into the blood as glucose. Their energy supply is instantaneous. They pass directly from the intestine into the blood.
They are carbohydrates that are rapidly assimilated, they do not require large or heavy digestion in order to be used. Those with a value greater than 70 are considered to have a high glycaemic index.