What If You Stop Eating For 72 Hours?

Listen to Dave Asprey explain the power of a 72-hour fast (12-minute episode excerpt)

In this episode of The Human Upgrade, Dave Asprey explains why a true 3-day (72-hour) fast can trigger deep cellular repair, reverse biological aging, and deliver benefits far beyond what short intermittent fasting (like 16:8) can achieve.

He walks through the science, the three distinct phases of fasting, common mistakes, and exactly how to prepare, execute, and refeed safely.

Why a 3-Day Fast Is Different

• Activates deep autophagy (cellular cleanup)
• Rebuilds stronger mitochondria
• Resets the immune system with fresh stem cells
• Increases BDNF for sharper memory and focus
• Reduces systemic inflammation
• Reverses biological aging markers

The Three Critical Phases of a 72-Hour Fast

Day 1: Burning Through Stored Sugar

Liver and muscle glycogen depletes. Insulin drops. Body begins tapping fat stores. This is usually the toughest day—hunger, mood swings, and low energy are common (unless you use ketone support like MCT or exogenous ketones).

Day 2: Full Ketosis & Autophagy Kicks In

Glycogen tanks are empty. Body runs primarily on fat and ketones. Inflammation drops. Old immune cells are recycled. Most people feel calm, clear-headed, and surprisingly energized.

Day 3: Peak Regeneration

Ketone levels peak. Stem cells activate. Mitochondria become more efficient. Brain receives extra energy and releases BDNF. This is when the anti-aging and longevity benefits are strongest.

Common Mistakes That Can Harm Your Fast

• Skipping electrolytes → headaches, cramps, heart palpitations
• High-intensity exercise → muscle breakdown
• Refeeding with junk food/pizza → insulin spike, inflammation rebound
• Doing long fasts too frequently → unnecessary stress on the body

How to Fast Safely & Effectively

Preparation (Day Before)

• Cut carbs and alcohol
• Hydrate deeply
• Load up on minerals (sodium, potassium, magnesium)

During the Fast

• Drink 2–3 liters of water daily with electrolytes or high-quality salt
• Stick to light activity: walking, gentle yoga, sauna
• Prioritize sleep and darkness at night
• Optional: black coffee/tea with MCT or butter for energy (still fasting)

Refeeding

• Start small: bone broth, eggs, wild salmon, grass-fed beef, cooked vegetables
• Avoid sugar, junk food, and alcohol
• Ease back into normal healthy eating over a day or two

Frequency: 3–4 times per year is plenty. Give your body time to rebuild between resets.

Final Thoughts from Dave

“We spend our whole lives adding things—supplements, routines, superfoods. Sometimes the most powerful thing you can do is just subtract. Remove food for 72 hours and watch your body remember what Mother Nature designed it to do: heal, rebuild, regenerate.”

— Dave Asprey

Source: The Human Upgrade podcast episode 1375 – “What If You Stop Eating For 72 Hours?”
Original episode: Apple Podcasts