Hunger is a feeling experienced when the glycogen level of the liver falls below a threshold, usually followed by a desire to eat. The usually unpleasant feeling originates in the hypothalamus and is released through receptors in the liver. Although an average nourished human can survive weeks without food intake, the sensation of hunger typically begins after several hours without eating.
Hunger can also be applied metaphorically to cravings of other sorts, e.g. "hungry for victory."
When hunger contractions occur in the stomach, the person sometimes experiences mild pain in the pit of the stomach, called hunger pangs. Hunger pangs usually do not begin until 12 to 24 hours after the last ingestion of food, in starvation. A single hunger contraction lasts about 30 seconds, and pangs continue for around 30-45 minutes, then hunger subsides for around 30-150 minutes. Individual contractions are separated at first, but are almost continuous after a time. Emotional states (anger, joy etc.) may inhibit hunger contractions. Levels of hunger are increased by lower blood sugar levels, and are higher in diabetics. They reach their greatest intensity in 3 to 4 days and may weaken in the succeeding days, though hunger never disappears. Hunger contractions are most intense in young, healthy people who have high degrees of gastrointestinal tonus. Periods between contractions increase with old age.
Satiety, or the feeling of fullness, is the disappearance of hunger after a meal. It is a process mediated by the ventromedial nucleus in the hypothalamus. It is therefore the "satiety center."
Therefore, satiety refers to the psychological feeling of "fullness" or satisfaction rather than to the physical feeling of being engorged, i.e. the feeling of physical fullness after eating a very large meal. Satiety directly influences feelings of appetite that are generated in the limbic system, and hunger that is controlled by neurohormones, especially serotonin in the lateral hypothalamus.lll
Hunger appears to increase activity and movement in many animals - for example an experiment on spiders showed increased activity and predation in starved spiders, resulting in larger weight gain. This pattern is seen in many animals, including humans while sleeping. It even occurs in rats with their cerebral cortex or stomachs completely removed. Increased activity on hamster wheels occurred when rats were deprived not only of food, but also water or B vitamins such as thiamine This response may increase the animal's chance of finding food, though it has also been speculated the reaction relieves pressure on the home population.
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- A. J. Carlson (1931) Hunger The Scientific Monthly 33: 77-79.
- A. J. Carlson; F. Hoelzel (1952) The Alleged Disappearance of Hunger during Starvation Science 115: 526-527.
- Provencher, L.; Riechert, S.E. (1991) Short-Term Effects of Hunger Conditioning on Spider Behavior, Predation, and Gain of Weight Oikos 62:160-166
- Wald, G.; Jackson, B. (1944) Activity and Nutritional Deprivation Proceedings of the National Academy of Sciences of the United States of America 30:255-263
- George Wald: The Origin of Death. Retrieved on 2007-05-14.
- Guerrant, N.B., Dutcher, R.A. (1940) Journal of Nutrition 20:589.
- Intergovernmental Institution for the use of Micro-algae Spirulina Against Malnutrition (IIMSAM)
- The Borgen Project
- Fighting Hunger and poverty in Ethiopia (Peter Middlebrook)
- Satiety enhancers in food Scientist Live