Science

Hormonal Effects of Intermittent Fasting Explained

Discover how intermittent fasting affects your hormones. Learn about changes to insulin, growth hormone, cortisol, and other key hormones during fasting.

13 min readUpdated January 2, 2026

Intermittent fasting creates profound hormonal changes that drive many of its benefits. Understanding these hormonal shifts helps you appreciate how fasting affects your body at a deeper level.

Insulin

Insulin is the primary hormone affected by fasting. During fasting periods, insulin levels drop significantly (by 20-31%), which allows your body to access and burn stored fat more effectively.

Human Growth Hormone (HGH)

Growth hormone can increase by 5x during fasting. HGH promotes fat burning, muscle preservation, and cellular repair. This increase is one reason IF helps maintain muscle while losing fat.

Norepinephrine

This stress hormone rises during fasting, increasing metabolic rate and stimulating the breakdown of fat for energy. This contributes to the metabolic boost some people experience while fasting.

Cortisol

Cortisol may briefly elevate during fasting (a natural stress response) but typically normalizes. Chronic elevation is a concern only with extreme fasting protocols or in those already stressed.

Hormonal BalanceFor most people, the hormonal changes from moderate IF (like 16:8) are beneficial. However, aggressive fasting can disrupt hormonal balance, especially in women. Listen to your body.

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.

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