The Cleansing stage is hours 24-48 of a fast, when autophagy - your cells' process of clearing out and recycling damaged components - ramps up meaningfully.
What's happening in your body
Autophagy (from the Greek for "self-eating") is a maintenance process where cells break down and recycle damaged proteins and organelles. It runs at a low level all the time, but prolonged fasting and low insulin appear to increase it. Around the 24-hour mark and beyond, your body leans further into fat and ketones for fuel while this cellular cleanup accelerates. Energy naturally dips - that's your body telling you to conserve.
Why this stage matters
Autophagy is the reason many people pursue extended fasts. While the exact human timing is still being researched, the 24-48 hour window is widely associated with increased autophagic activity. The right approach here is restraint: gentle movement, rest, and calm. Pushing hard workouts now works against the conservation your body is asking for.
What your biometrics show
Expect a lower Body Battery and possibly reduced HRV as the fast extends - normal signs of an extended fast. FastFlow keeps reading your live biometrics so you can tell the difference between normal fatigue and a signal to stop.
What to do during the Cleansing stage
- Meditation and reflection
- Gentle walks - nothing strenuous
- Read, journal, or do calm creative work
- Breathwork to manage energy and stress
Frequently asked questions
When does autophagy start during fasting?
Autophagy runs continuously at a low level but appears to ramp up meaningfully during prolonged fasting, generally associated with the 24-48 hour window - the Cleansing stage. Exact human timing varies and is still being studied.
Is a 24-hour fast safe?
For many healthy adults, occasional 24-hour fasts are well tolerated, but extended fasting isn't right for everyone. If you're pregnant, under 18, have a history of disordered eating, or manage a medical condition, talk with a healthcare professional first. FastFlow provides general wellness information, not medical advice.
Why do I feel tired at 24-36 hours of fasting?
Lower energy in the Cleansing stage is normal - your body is conserving resources and leaning on fat and ketones while autophagy ramps up. Rest, gentle movement, and electrolytes help; extreme fatigue or feeling unwell is a signal to break the fast.