Beginner's Guide
How to Do a 72-Hour Water Fast: Complete Guide
Ready for your first 3-day fast? This guide covers everything: preparation, what to expect each day, managing electrolytes, and how to break your fast safely.
In This Guide
Before You Start: Is a 72-Hour Fast Right for You?
❌ Do NOT fast if you:
- • Are pregnant or breastfeeding
- • Have a history of eating disorders
- • Have type 1 diabetes or take insulin
- • Are underweight (BMI under 18.5)
- • Have severe kidney or liver disease
- • Take medications that require food
- • Are under 18 years old
⚠️ Consult a doctor first if you:
- • Have type 2 diabetes
- • Take any prescription medications
- • Have heart conditions or high blood pressure
- • Have gout or kidney stones
- • Have any chronic health conditions
- • Have never fasted for more than 24 hours
✓ Good candidates for a 72-hour fast:
- • Healthy adults with no contraindications
- • Have experience with shorter fasts (16-24 hours)
- • Have a BMI of 18.5 or higher
- • Can take time off from intense physical activity
- • Have access to electrolytes and can rest if needed
Preparation: 3-7 Days Before
Proper preparation makes the fast significantly easier. Here's how to set yourself up for success:
1. Reduce Carbohydrates (3-5 days before)
Gradually lower your carb intake to 50-100g per day. This pre-depletes glycogen stores and makes the transition to ketosis much smoother. You'll experience less hunger and fewer side effects.
2. Cut Caffeine (3-5 days before)
If you drink coffee daily, gradually reduce intake to avoid withdrawal headaches during your fast. You can still have black coffee during the fast, but starting with lower dependence helps.
3. Practice Shorter Fasts
If you've never fasted beyond 12-16 hours, try a 24-hour fast first. This gives you confidence and helps you understand how your body responds to fasting.
4. Schedule Wisely
Plan your fast during a low-stress period. Avoid starting before important work deadlines, social events with food, or intense physical activities. Weekends or time off work ideal.
5. Last Meal
Make your last meal moderate in size, high in protein and fat, low in carbs. Avoid a "last supper" mentality — overeating makes the first day harder. Example: salmon with vegetables and avocado.
What You Need
Essential
- ✓ Water (2-3 liters per day)
- ✓ Electrolytes (sodium, potassium, magnesium)
- ✓ Sea salt or Himalayan pink salt
- ✓ Refeeding foods (bone broth, eggs)
Helpful
- ○ Black coffee or plain tea
- ○ Sparkling water (variety helps)
- ○ Electrolyte powder (sugar-free)
- ○ Fasting tracker app
💡 Electrolyte Recommendation
Daily targets during your fast: 2000-3000mg sodium, 1000-2000mg potassium,300-400mg magnesium. You can use electrolyte powders (check for zero calories) or make "snake juice" (water with salt and potassium chloride).
Day-by-Day: What to Expect
Day 1 (Hours 0-24)
The Adjustment Phase
What happens: Your body depletes liver glycogen and begins transitioning to fat-burning. Insulin drops, growth hormone rises.
How you'll feel: Hunger peaks around hours 18-24. You may feel irritable, have low energy, or experience mild headaches. This is normal.
Tips: Stay busy, drink plenty of water with electrolytes, go for a walk (helps deplete glycogen faster). Hunger comes in waves — it will pass.
Day 2 (Hours 24-48)
The Breakthrough
What happens: Full ketosis established. Autophagy significantly increasing. Growth hormone peaks at 5x normal. BDNF elevating.
How you'll feel: Paradoxically, many people feel BETTER on day 2. Mental clarity improves, hunger often decreases. You may feel calm and focused.
Tips: This is often the easiest day. Take advantage of the mental clarity. Light activity is fine. Keep up with electrolytes.
Day 3 (Hours 48-72)
Peak Benefits
What happens: Peak autophagy. Stem cell regeneration activating. Immune system reset in progress. Maximum cellular renewal.
How you'll feel: Energy may dip slightly as your body focuses on cellular cleanup. Many report profound mental clarity and calm. Hunger is usually minimal.
Tips: Take it easy. Light walking is fine, but avoid intense exercise. Start planning your refeed. You're almost there!
Track Your Progress in Real-Time
Our app shows you exactly which phase you're in, what's happening in your body, and when you'll hit each milestone.
Start Tracking FreeElectrolyte Management
Proper electrolyte intake is critical for a safe fast. Without food, you're not getting electrolytes, and depletion can cause headaches, muscle cramps, dizziness, and in severe cases, heart issues.
| Electrolyte | Daily Target | Sources |
|---|---|---|
| Sodium | 2000-3000mg | Sea salt, Himalayan salt, bouillon |
| Potassium | 1000-2000mg | No-salt (KCl), electrolyte powders |
| Magnesium | 300-400mg | Magnesium citrate/glycinate supplements |
Warning Signs of Electrolyte Depletion
If you experience severe headaches, muscle cramps, heart palpitations, dizziness, or confusion — take electrolytes immediately. If symptoms persist, break your fast and consult a doctor.
How to Break Your Fast Safely
Breaking a 72-hour fast correctly is just as important as the fast itself. Your digestive system has been resting — don't shock it with a huge meal.
✓ Good First Foods
- • Bone broth (warm, soothing, easy to digest)
- • Scrambled eggs (protein without fiber stress)
- • Avocado (healthy fats, gentle)
- • Small portion of fish (salmon, etc.)
- • Cooked vegetables (not raw initially)
✗ Avoid for First 24 Hours
- • Large meals (eat small, wait 2-3 hours between)
- • Raw vegetables and high-fiber foods
- • Nuts and seeds (hard to digest)
- • Dairy (can cause digestive upset)
- • Alcohol (hits much harder post-fast)
- • Sugar and processed foods
Pro Tips for Success
Walk on Day 1
Light walking helps deplete glycogen and speeds up ketosis transition
Drink More Than You Think
Aim for 2-3 liters per day. Add electrolytes to at least some of it
Black Coffee is Your Friend
Caffeine suppresses appetite and may boost autophagy
Rest When Needed
Your body is doing cellular housekeeping. Honor its need for rest
Avoid Food Content
Don't torture yourself watching cooking shows or scrolling food pics
Hunger Passes
Hunger comes in waves of 20-30 min. Distract yourself and it will pass
You May Feel Cold
Metabolism slows slightly. Keep a sweater handy, take warm showers
Remember Your Why
Write down why you're fasting. Refer to it when things get tough
Ready to Begin?
You've got the knowledge. Now track your fast with our free app — see your phases in real-time, get supplement guidance, and know exactly when to refeed.
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