Energy metabolism starvation

During periods of hunger, muscle proteins serve as an energy reserve for the body. They are broken down into amino acids, which are transported to the liver. In the liver, the carbon skeletons of the amino acids are converted into intermediates in the tricarboxylic acid cycle or into acetoacetyl-CoA (see p. 175). These amphibolic metabolites are then available to the energy metabolism and for gluconeogenesis. After prolonged starvation, the brain switches to using ketone bodies in order to save muscle protein (see p. 356). 

The major events in fuel storage and energy utilization are summarized in table 24.2. In this table, energy metabolism is considered under conditions of glucose excess, such as just after a meal under conditions when the glucose supply is scant, as after prolonged periods between meals and under starvation conditions, when the glucose supply is severely limited. 

During starvation, body fats replace dietary carbohydrates as a major source of energy. Metabolism of these fats yields organic acids such as acetoacetic acid. This causes a mild metabolic acidosis. In strenuous exercise, particularly in a trained athlete, fats are preferentially metabolized also, in exercise sufliciently strenuous to exceed the anaerobic threshold, lactic acid is released into the extracellular fluid in all subjects, both the trained athlete and the normal person. Fever and trauma such as extensive bums or major surgery result in tissue breakdown this catabolism results in the release of organic acids into the extracellular fluid. 

Hyperactivity of the orexin system, e.g. triggered by energy depletion, metabolic failure, hypoglycemia or hypoxia, in the context of starvation, sleep derivation, and stress, may predispose to addiction and... 

Dnring starvation there is a decrease in the resting energy expenditnre which is due to reduced metabolic activity in most tissnes including, perhaps surprisingly, the brain. The decrease in muscle protein breakdown may, therefore, be a simple consequence of a decrease in the rate of glucose oxidation, so that gluconeogenesis from the amino acids is decreased. 

Gerald, V.M. (1976). The effect of starvation on energy turnover and protein metabolism in Ophiocephalus punctatus. Hydrobiologia 49,131-201. 

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