J E Bines and R G Heine, University of Melbourne,
Melbourne, VIC, Australia
© 2005 Elsevier Ltd. All rights reserved.
During a normal 24-h day the body's essential cellular and organ functions remain homeostatic despite intermittent nutrient intake and changing metabolic demand. A highly sophisticated and integrated system provides the metabolic adaptation for these normal changes in substrate provision and utilization. A basic knowledge of the normal metabolic responses in the feeding-fasting cycle is pivotal to the understanding of the changes that occur during periods of prolonged fasting and starvation. In this review of the biochemical aspects of the metabolic responses to fasting and starvation, the term 'fasting' is defined as the total absence of nutrient intake, whereas 'starvation' is defined as a prolonged period of inadequate food intake. During a period of prolonged fasting, the body undergoes a sequence of changes that include the initial depletion of fuel stores and metabolic adaptation. However, if fasting continues, metabolic decompensation will occur, finally resulting in death. The extent and rate of progression through these steps depend on the amount of fuel stores at initiation of the fast, the severity and duration of nutritional deprivation, and the presence or absence of a significant catabolic stress, such as injury, sepsis, or cancer (Table 1).
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