Complete Timeline
72-Hour Fast Timeline: What Happens Hour by Hour
A detailed breakdown of what's happening in your body during each phase of a 3-day water fast — from fed state to peak autophagy and beyond.
Quick Reference
Fed State
Hours 0-4What's Happening
Your body is digesting your last meal. Blood sugar rises, insulin is released, and nutrients are being absorbed and stored.
How You'll Feel
Normal. You won't feel like you're fasting yet.
Key Changes
Early Fasting
Hours 4-12What's Happening
Digestion complete. Your body begins using stored glycogen for energy. Insulin starts dropping, and fat-burning begins.
How You'll Feel
You might start noticing hunger, especially around normal meal times. Generally manageable.
Key Changes
Glycogen Depletion
Hours 12-18What's Happening
Liver glycogen is depleting. Your body is transitioning from glucose to fat-burning. Ketone production begins.
How You'll Feel
This is often the hardest part. Hunger peaks, you may feel low energy, irritable, or have headaches.
Key Changes
Ketosis
Hours 18-24What's Happening
You've entered ketosis. Your body is now primarily burning fat for fuel. Blood ketones reach 0.5-1.5 mmol/L.
How You'll Feel
Energy often improves. Hunger typically decreases significantly. Mental clarity may begin improving.
Key Changes
Autophagy Accelerates
Hours 24-36What's Happening
Autophagy significantly increases. Your cells are actively recycling damaged components. Growth hormone peaks at ~5x normal.
How You'll Feel
Many people feel surprisingly good. Mental clarity improves, hunger is often minimal. Energy is stable.
Key Changes
Peak Autophagy
Hours 36-48What's Happening
Autophagy reaches peak levels. Maximum cellular cleanup is occurring. Old, damaged proteins and organelles are being recycled.
How You'll Feel
Often the 'best' feeling day. Mental clarity peaks for many. Hunger is usually very low. Calm, focused energy.
Key Changes
Immune Reset Begins
Hours 48-60What's Happening
Stem cells begin activating. Old immune cells continue to be cleared, making way for regeneration upon refeeding.
How You'll Feel
Energy may dip slightly as body focuses on cellular work. Continued mental clarity. Minimal hunger.
Key Changes
Deep Renewal
Hours 60-72What's Happening
You're in the final stretch. Maximum benefits are being achieved. Your body has undergone significant cellular renewal.
How You'll Feel
A sense of accomplishment. Energy varies. Some feel great, others ready to refeed. Both are normal.
Key Changes
After 72 Hours: Breaking Your Fast
Congratulations — you've completed a 72-hour fast! How you break your fast is just as important as the fast itself. Here's what to do:
- ✓Start with bone broth or a small portion of eggs
- ✓Wait 2-3 hours between small meals
- ✓Avoid large meals, sugar, and alcohol for 24 hours
- ✓Eat slowly and stop when 70% full
Day-by-Day Summary
Day 1
The challenge day. Hunger peaks around 18-24 hours. Push through — it gets easier.
Day 2
The breakthrough day. Hunger fades, clarity arrives. Many feel better than Day 1.
Day 3
The peak day. Maximum benefits, minimal hunger. Calm, focused, accomplished.
Track Every Phase in Real-Time
Our free app shows you exactly which phase you're in, what's happening in your body, and counts down to each milestone.
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