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Updated: Oct 4, 2025

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Physiological responses to acute fasting: implications for intermittent fasting programs.

Matthew T Stratton1, Kembra Albracht-Schulte1, Patrick S Harty1

  • 1Energy Balance and Body Composition Laboratory; Department of Kinesiology and Sport Management, Texas Tech University, Lubbock, Texas, USA.

Nutrition Reviews
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Summary
This summary is machine-generated.

Intermittent fasting (IF) rapidly impacts glucose and lipid metabolism within 24 hours. However, effects on protein metabolism and autophagy during acute fasting require further investigation for optimal IF interventions.

Keywords:
autophagyexercisefree fatty acidglucoseinsulinketonemetabolism

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Area of Science:

  • Metabolic Physiology
  • Nutritional Science
  • Cellular Biology

Background:

  • Intermittent fasting (IF) is a popular dietary approach with extensive research on long-term effects.
  • Limited understanding exists regarding the acute physiological responses during typical IF fasting periods.

Purpose of the Study:

  • To review the acute physiological responses during short-term fasting.
  • Focus on substrate metabolism, systemic hormones, and autophagy.

Main Methods:

  • Literature search for studies on acute fasting and short-term starvation.
  • Synthesis of findings on physiological alterations within the initial 24 hours of fasting.

Main Results:

  • Acute fasting alters glucose and lipid metabolism within 24 hours.
  • Minimal changes observed in protein metabolism during this timeframe.
  • The impact of acute fasting on autophagy remains largely undetermined.

Conclusions:

  • Acute fasting elicits rapid metabolic shifts in glucose and lipids.
  • Further research is needed to understand protein metabolism and autophagy during fasting.
  • Findings aid in contextualizing IF research and developing future interventions.