Intermittent fasting isn't just about skipping meals—it triggers a cascade of biological changes that affect nearly every system in your body. Understanding the science helps you appreciate why IF is so effective.
The Metabolic Switch
After 12-36 hours of fasting, your body undergoes a 'metabolic switch' from using glucose as its primary fuel to using fatty acids and ketones. This switch triggers many of fasting's benefits.
Hormonal Changes During Fasting
- Insulin: Drops significantly, allowing fat burning
- Growth Hormone: Increases up to 5x, supporting muscle and fat metabolism
- Norepinephrine: Rises, boosting metabolism and fat breakdown
- Cortisol: Brief elevation, then normalizes
- Leptin and Ghrelin: Hunger hormones adjust over time
Cellular and Molecular Changes
- Autophagy activation: Cellular cleanup increases
- Gene expression changes: Longevity genes activate
- Inflammation reduction: Inflammatory markers decrease
- Oxidative stress: Reduced damage to cells
- BDNF production: Brain health support increases
Timeline of Changes0-4 hours: Glucose being used | 4-12 hours: Glycogen depleting | 12-18 hours: Fat burning begins | 18-24 hours: Ketosis and autophagy increase | 24+ hours: Deep autophagy and cellular repair
Related Topics
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Medical Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. Always consult with a qualified healthcare provider before starting any fasting regimen.