When we look at the evolution of human beings, in years gone by, when we lived in caves we would get the signal of hunger.  It could have been a rumbling stomach, feeling listless, jelly legs and even hangry.

This signal of hunger alerted us to go scavenge and forage for food, we went hunting and gathering the food to eat.  It could be a few hours or longer before we had any food to eat. This was the normal purpose of hunger signals back then. When food was plentiful, depending on the season, we ate well and put on weight in the form of fat.  This fat was important as it provided the fuel we needed to survive in the winter months or times when food was scarce.