The glycemic index or GI is a measure of the increase in blood sugar levels after a meal.
Carbohydrates that are rapidly broken down during digestion and release their glucose quickly into the bloodstream have a high glycemic index. Foods with a low GI do not cause a blood sugar levels to rise and therefore cause no insulin peak.
Insulin makes you hungry. When eating foods with a high GI, insulin production quickly increases. The released sugar is quickly transported to the cells where it is absorbed. The sugar has been absorbed, but is there still insulin in the blood? The result is that the cells are fed, yet the sugar concentration in the blood rapidly decreases, which you experience as a hunger craving.