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Phase 1: First 4-6 hours after eating — normal digestion
After eating, your body is busy with digestion. Glucose from food is converted into energy, and insulin is released to transport glucose into cells.
- Insulin is the “storage hormone” — when it's high, the body doesn't burn fat.
- Glucose, not fat, is mainly used for energy.
In this phase, the body is still in “feeding mode” and fat burning is minimal.
Phase 2: 6-12 hours after the last meal — decreased insulin and the start of fat burning
As digestion ends, insulin levels begin to decrease. The body begins to look for other sources of energy, and now it comes into play stored fat.
- Glycogen reserves (sugar stored in the liver and muscles) begin to be consumed.
- Fat burning begins gradually.
- The feeling of hunger may appear, but it is temporary and generally disappears after 15-20 minutes.
Phase 3: 12-16 hours — autophagy and growth hormone release
This is where things get really interesting. Once the body is short of glucose and insulin is low, it enters a state of internal cleaning.
- Autophagy: the process by which cells destroy and recycle old, damaged or dysfunctional components.
- It is released growth hormone(GH), which helps with cell repair and preservation of muscle mass.
- The brain can benefit from increased mental clarity.
This phase is essential for those who want more than weight loss — cellular detox, prevention, regeneration.
Phase 4: 18-24+ hours — ketosis and stable energy from fat
At this stage, the body enters ketosis: begins to produce ketone bodiesfrom fats, which become the main source of energy for the brain and body.
- Ketones provide clean energy without sudden blood glucose fluctuations.
- Inflammation decreases, and many people say they feel “light” or “clear in mind.”
- It is an intense but beneficial metabolic state.
This phase occurs especially in protocols of type 20/4, OMAD or posts longer than 24h (with supervision).
What else happens in parallel?
✅ Insulin sensitivity increases— cells become more responsive to insulin, which helps prevent diabetes.
✅ Reduction of chronic inflammationFasting can reduce inflammatory markers in the body.
✅ Reset the taste— after a 14-16 hour break, your taste buds become more sensitive, and healthy foods start to seem tastier to you.
✅ Appetite regulation— the hormones of hunger (ghrelin) and satiety (leptin) begin to regulate naturally, without extreme diets.
Important: Every body is different
Each organism reacts differently. Some feel the clear effects after a few days, others need 2-3 weeks of adaptation. It is perfectly normal. Listen to your body, write down how you feel, and adjust your fasting protocol according to your own reactions.
We hope this article gave you a clear picture of what happens in the body during fasting. If you are at the beginning, start gradually, be consistent and you will feel the benefits to the fullest.
And if you have any questions or personal experiences, we invite you to write to us — we are here to learn from each other.
Do you want to lower your inflammation and increase your natural energy?
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Fat burning usually begins after 10—12 hours of fasting, when glycogen reserves are low and insulin is reduced.
Autophagy is a process by which your cells clean their damaged parts. It is activated after 14—16 hours of fasting and helps in cell regeneration and detoxification.
No, IF it is done correctly. Growth hormone increases during fasting and helps protect muscle mass, especially if you feed properly in the food window.
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