Hunger can be defined as starvation a physiological drive to find and eat food a sensation caused by distension of the stomach and small intestine a psychological desire to eat

Hunger is a physiological drive to find and eat food.
Hunger is influenced by hormones, there are two major hormones that tip the balance between hunger and fullness; these are leptin and ghrelin. Leptin is released from the body's long term fat stores, and suppresses hunger while gherlin causes the stomach rumblings as a physical reminder to eat, which brings the drive to want to find and eat food. 

Molecules called lipids have long hydrocarbon chains that determine the way they act. they can be fats, oils, or hormones, and even exist in our cell membranes