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Energy metabolism in feasting and fasting
Advances in Experimental Medicine and Biology
|January 1, 1979
Summary
This study explains how the body uses and stores nutrients after eating and conserves fuel during fasting. It highlights the coordinated roles of organs in maintaining energy balance and surviving starvation.
Area of Science:
- Metabolic regulation
- Human physiology
- Nutrient metabolism
Background:
- Post-meal metabolic rate, body temperature, and respiratory quotient increase with nutrient intake.
- Dietary components replenish glycogen and fat stores; excess carbohydrate converts to lipid.
- Excess amino acids are catabolized due to lack of storage and nitrogen toxicity.
Purpose of the Study:
- To describe the metabolic adaptations during feasting and fasting.
- To elucidate the roles of various tissues in fuel homeostasis.
- To explain survival mechanisms during caloric deprivation.
Main Methods:
- Review of metabolic processes during fed and fasted states.
- Analysis of fuel utilization and storage.
- Examination of hormonal and tissue interactions.
Main Results:
- Feasting involves nutrient storage and conversion to fat.
- Fasting initially relies on glycogenolysis and lipolysis, then shifts to protein sparing.
- Ketone bodies and free fatty acids become primary fuels during prolonged starvation.
- Kidneys conserve ketone bodies, preventing fuel loss.
Conclusions:
- The liver, muscle, kidney, and adipose tissue collaborate to maintain blood fuel homeostasis.
- This metabolic interplay enables survival during extended periods of caloric deprivation.