Starvation is a severe deficiency in caloric energy intake needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death.

The basic cause of starvation is an imbalance between energy intake and energy expenditure. In other words, the body expends more energy than it takes in. This imbalance can arise from one or more medical conditions or circumstantial situations, which can include: Anorexia nervosa, Bulimia nervosa, celiac disease, diabetes mellitus etc.

Early symptoms include impulsivity, irritability, hyperactivity, and other symptoms. Atrophy (wasting away) of the stomach weakens the perception of hunger, since the perception is controlled by the percentage of the stomach that is empty. Individuals experiencing starvation lose substantial fat (adipose tissue) and muscle mass as the body breaks down these tissues for energy.

Catabolysis is the process of a body breaking down its own muscles and other tissues in order to keep vital systems such as the nervous system and heart muscle (myocardium) functioning. The energy deficiency inherent in starvation causes fatigue and renders the victim more apathetic over time. As the starving person becomes too weak to move or even eat, their interaction with the surrounding world diminishes. In females, menstruation ceases when the body fat percentage is too low to support a fetus.

Victims of starvation are often too weak to sense thirst, and therefore become dehydrated. All movements become painful due to muscle atrophy and dry, cracked skin that is caused by severe dehydration. With a weakened body, diseases are commonplace. Fungi, for example, often grow under the esophagus, making swallowing painful. Vitamin deficiency is also a common result of starvation, often leading to anemia, beriberi, pellagra, and scurvy. These diseases collectively can also cause diarrhea, skin rashes, edema, and heart failure. Individuals are often irritable and lethargic as a result.

There is insufficient scientific data on exactly how long people can live without food. Although the length of time varies with an individual's percentage of body fat and general health, one medical study estimates that in adults complete starvation leads to death within 8 to 12 weeks. There are isolated cases of individuals living up to 25 weeks without food. Starvation begins when an individual has lost about 30% of their normal body weight. Once the loss reaches 40% death is almost inevitable.

Starving patients can be treated, but this must be done cautiously to avoid refeeding syndrome. Rest and warmth must be provided and maintained. Small sips of water mixed with glucose should be given in regular intervals. Fruit juices can also be given. Later, food can be given gradually in small quantities. The quantity of food can be increased over time. Proteins may be administered intravenously to raise the level of serum proteins.

Starvation may be associated with several diseases including: 

Anorexia nervosa

Anorexia nervosa is a common eating disorder, particularly in women, with a lifetime prevalence estimated to be 0.3–0.9%. Anorexia nervosa is associated with numerous general medical complications. The complications affect almost all major organ systems and often also include physiologic disturbances such as hypotension (low blood pressure), bradycardia (a slow heart rate ) and hypothermia (reduced body temperature). 

In general, medical complications of anorexia nervosa are a direct result of weight loss and malnutrition. Starvation induces protein and fat catabolism that leads to loss of cellular volume and function, resulting in adverse effects on, and atrophy of, the heart, brain, liver, intestines, kidneys, and muscles.

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Sources

Anorexia nervosa – medical complications ―by Mehler and Brown licensed under CC BY 4.0
Starvation ―sourced from Wikipedia licensed under CC BY-SA 3.0
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