Autophagy starts ramping up significantly around 16-24 hours after your last meal, though the exact timing varies based on individual metabolism, prior diet, activity level, and metabolic health.

Why it Takes That Long

Your body prioritises readily available fuel sources first:

1. 0-6 hours: Burning glucose from your last meal
1. 6-12 hours: Depleting liver glycogen stores
1. 12-16 hours: Transitioning to fat burning (ketosis begins)
1. 16-24+ hours: Insulin drops to baseline, triggering cellular cleanup processes including autophagy

Autophagy is essentially your cells’ recycling system—breaking down damaged proteins, organelles, and cellular debris. But this only happens when nutrient signalling (particularly insulin and mTOR) is low enough to signal “scarcity mode.”

Autophagy deepen with longer fasts?

Autophagy increases progressively:

– 24 hours: Autophagy is well-established
– 36-48 hours: Deeper autophagic activity, more extensive cellular cleanup
– 72+ hours: Autophagy peaks, along with stem cell regeneration and immune system renewal

The longer the fast, the more profound the cellular recycling—but also the more challenging for most people to sustain.

Key factor: People with insulin resistance take longer to enter deep autophagy because they have higher baseline insulin and larger glycogen stores to deplete first.