Fasting has become one of the most talked-about health practices in recent years. From intermittent fasting to prolonged multi-day fasts, people are experimenting with abstaining from food in hopes of weight loss, improved metabolism, and disease prevention.
But fasting isn’t for everyone. Done incorrectly—or without understanding your body’s condition—fasting can be risky, even life-threatening, especially for older adults or people with underlying health issues like heart conditions.
This article covers:
- The different types of fasting
- What the actual benefits are and when they occur
- Who should and shouldn’t fast
- How to fast safely
- Why 72-hour+ fasts are not safe for everyone
Types of Fasting
1. Intermittent Fasting (IF)
Most Popular & Safest Approach
- Time-Restricted Eating (TRE): Example: 16:8 method (16 hours fasting, 8 hours eating)
- One Meal a Day (OMAD): Eating one large meal within a 1-2 hour window
- 5:2 Fasting: Eat normally for 5 days, restrict calories to 500-600 on 2 non-consecutive days
Primary Benefits:
- Blood sugar regulation
- Fat metabolism
- Digestive system rest
- Reduced inflammation
2. 24-Hour Fast
- No food for a full day (dinner-to-dinner or lunch-to-lunch)
Primary Benefits:
- Enhanced insulin sensitivity
- Autophagy begins (cellular clean-up)
- Reduced oxidative stress
3. 36-Hour Fast
- Finish dinner on Day 1, eat breakfast on Day 3
Primary Benefits:
- Extended autophagy
- Deepened fat burning
- Possible stem cell stimulation
Caution: Can cause electrolyte depletion, hormone imbalance, and cortisol spikes in older adults or those with medical conditions.
4. 72-Hour Fast (3-Day Fast)
The “Deep Cleanse” Fast — but also the most dangerous
- No food for 72 hours
- Only water, salt, electrolytes
Alleged Benefits (for healthy, younger people):
- Significant autophagy and immune system reset
- Improved insulin sensitivity
- Stem cell regeneration (mainly seen in animal studies)
- Ketone production and deep fat metabolism
Warning: For people over 60, or anyone with cardiovascular disease, metabolic disorders, or other health concerns, this fast can trigger:
- Severe electrolyte depletion
- Dangerous blood pressure drops
- Elevated cortisol and heart rate
- Muscle wasting
- Heart rhythm disturbances
- Syncope (fainting)
- Potential cardiac events
This is NOT a safe fast for everyone.
When Fasting Benefits Actually Happen
| Time into Fast | What Happens | Benefits |
|---|---|---|
| 0-12 hrs | Blood sugar lowers, insulin drops | Initial fat burning begins |
| 12-16 hrs | Glycogen stores deplete | Fat metabolism increases |
| 16-24 hrs | Ketones increase, HGH rises | Mental clarity, fat burning |
| 24-36 hrs | Autophagy ramps up | Cellular cleanup, reduced inflammation |
| 36-48 hrs | Cortisol spikes, gluconeogenesis starts | Stress hormones increase |
| 48-72 hrs | Deep ketosis, increased autophagy | Immune reset, but also high body stress |
| 72+ hrs | Severe stress response, lean tissue loss | Risk increases significantly |
Who Should NOT Attempt Extended Fasting
Do not attempt a fast longer than 24-36 hours if you:
- Are over 60 years old (especially without experience)
- Have any heart condition, arrhythmia, or history of heart attack
- Have diabetes or blood sugar instability
- Take medications that affect blood pressure, blood sugar, or electrolytes
- Have kidney disease
- Suffer from adrenal or thyroid disorders
- Are underweight or recovering from illness
How to Fast Safely
Start Small: Begin with 12-16 hour intermittent fasts and only increase when you’re confident in your recovery and overall health.
Prioritize Electrolytes: Use salt, potassium, and magnesium during any fast over 16 hours.
Listen to Your Body: If you feel dizzy, weak, or your heart rate spikes, stop fasting and eat.
Refeed Properly: Break fasts with bone broth, light protein, and clean carbs. Avoid junk, high fats, or heavy meals.
Rest & Recover: Avoid heavy workouts, saunas, or fasting during high-stress periods.
The Dangers of 72-Hour Fasting
Despite what influencers and health blogs say, 72-hour fasts are not universally safe. For older adults or those with any health condition, especially involving the heart, these long fasts can be dangerous.
Symptoms that signal you’re in danger:
- Irregular or racing heart rate
- Dizziness or lightheadedness
- Chest pain or discomfort
- Muscle cramps
- Brain fog or confusion
- Sudden weakness or shakiness
Just because a 30-year-old athlete or biohacker can handle it doesn’t mean it’s right for you. You are not broken if a long fast overwhelms your system. It is a powerful metabolic stressor — and must be treated with respect.
Final Thoughts: Fasting Can Heal — But It Can Also Harm
Fasting has legitimate health benefits when done intelligently, especially intermittent fasting and short-term fasts. For older adults, a consistent 16:8 schedule paired with light strength training, clean eating, and good sleep can deliver many of the same benefits of extended fasts without the risk.
Know your body. Start slow. Respect the fast.
If you have underlying health issues, talk to your doctor or a functional medicine provider before attempting anything over 24 hours. Health is not a race to extremes. It’s about sustainable, long-term habits that support your body, not shock it.
