Hunger is an unpleasant feeling caused by the body’s need for food. Hunger is associated with various sensations in the stomach, as well as with weakness or faintness. The severe hunger pains called stomach cramps are produced by strong contractions of the stomach muscles. Many experts believe that hundreds of millions of children and adults around the world suffer from long-term hunger.
Certain chemicals produced in the brain and in other organs and tissues play an important role in regulating the awareness of hunger in human beings. An imbalance of these chemicals can increase or decrease hunger. The amounts of certain substances in the blood, such as the hormones cholecystokinin, insulin, and leptin, affect hunger. Cholecystokinin, made by the small intestine, reduces hunger for short periods. Insulin from the pancreas and leptin, made by fat cells, influence food intake and energy levels over longer periods.
The amount of glucose, a sugar, in the blood also affects hunger. People may become hungry if their bodies have less than a normal amount of glucose. But people need many substances besides glucose to avoid being hungry and for growth and good health. These substances include fats, vitamins, minerals, and amino acids.
Sensitive receivers called internal chemoreceptors respond to the amount of available glucose and other nutrients in the body (see Senses). These receptors, which are in the brain, liver, digestive tract, and elsewhere in the body, also respond to hormones that control metabolism. The receptors send nerve impulses to an area of the brain stem called the hypothalamus. The hypothalamus analyzes the impulses to determine a person’s level of hunger. This analysis may motivate a person to eat foods that contain substances that he or she is lacking.
Habits also affect hunger and eating. People eat at certain times, and they usually eat only certain foods. Social factors—for example, the presence of other people—can influence the quantity and kinds of food a person eats.
Hunger is one of the world’s main social problems. In both developing and developed countries, millions of people are too poor to raise or buy enough food. Furthermore, the world’s growing population creates a greater demand for food every year. But droughts, floods, or other natural disasters destroy many food crops annually. Many developing countries lack the expertise and equipment needed to produce adequate food supplies for their people. Hunger differs from famine, which is a prolonged food shortage in a certain geographic area (see Famine).
