Hunger is a feeling experienced by animals when the glycogen level of the liver falls below a certain point. The usually unpleasant feeling originates in the hypothalamus and is released through receptors in the liver and stomach. An average nourished human can survive about 50 days without food intake, but only three days without fluids. Hunger can also be applied metaphorically to cravings of other sorts.
The term is commonly used more broadly to refer to cases of widespread malnutrition or deprivation among populations, usually due to poverty, political conflicts or instability, or adverse agricultural conditions (famine).
Hunger as a condition
The term hungry is commonly used to mean having an appetite for food or to be ready for a meal. After a long period without food, the mild sensation of hunger associated with being ready for a meal becomes progressively more severe, until it is acutely painful. As hunger grows, most living things will experience some internal effects. In humans and other animals, hunger can cause a gurgling sound with a bubbling feeling in the small intestine (many mistakenly think the stomach does this), and can shrink the stomach. Prolonged hunger will drive people to eat substances with no nutritional value (such as grass and soil) simply to fill their stomachs, but doing so actually has an adverse effect on energy balance as energy is still required to digest these substances.
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