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Starvation is the state of being when insufficient calorific intake is being ingested in order to maintain body weight. It is often taken to mean a reduction in eating, but it may also be due to defective absorption. It is one form of malnutrition and it forms a spectrum with the changes of fasting; fasting implies a greater element of active decision not to eat. In hardy individuals with supplementation of just water, absolute fasting can continue for around 100 days.
Fasting is most commonly exhibited in the hospital environment in pre- and post-operative patients who are kept 'nil by mouth'.
Physiologically, the changes of starvation can be divided up on a temporal basis:
- first 24 hours:
- muscle protein and fat are the primary energy sources
- glucose reserves from glycogenolysis last only for the first day
- then, glycerol from fat and amino acids from muscle are converted by gluconeogenesis in the liver to glucose. Glucose is used as the energy source for the brain, erythrocytes and leucocytes, the bone marrow, and the renal medulla.
- prolonged starvation (days to weeks):
- the degradation of muscle protein can no longer be maintained and it is reduced from 10g/day to 3-4 g
- after about 3 weeks, the brain converts from its energy supply to ketone bodies produced from fat breakdown
- ketones begin to appear in urine
Last reviewed 01/2018