Why do people always feel hungry?

Human physiological activity energy directly comes from blood sugar, blood sugar comes from the small intestine and other digestive organs from food nutrients. Hunger is caused by the blood sugar concentration in the decrease, and then there will be normal physiological reaction. This time should supplement food (that is, eat), if this time do not immediately supplement food, a little longer, physiological reaction will promote the decomposition of liver glycogen, this time people will feel hungry past, but not hungry.