Sugar levels in blood fall to indicate hunger. The brain is dependent on Sugar as its primary energy producing substance. Low Blood Sugar indicates to the brain that there is need for food intake and this triggers sensations of hunger. Sugar is absorbed from the intestines and via blood stream it reaches the liver and various body cells to provide the primary source of energy for body's cells. Sugar levels rise after meals for an hour or two by a few grams and are usually lowest in the morning, before the first meal of the day. The morning levels are the lowest since it follows around 6 to 8 hours of fasting throughout the night.