What is autophagy?
Autophagy is the recycling system inside your cells: it collects worn-out and broken parts, breaks them down and reuses the materials.
Think of a city's garbage collection and recycling service. Trucks pick up broken furniture and old packaging, and the materials get turned into something new. When collection slows down, junk piles up in the streets.
Why it matters for aging
The word comes from Greek: "auto" (self) and "phagy" (eating). Cells literally digest their own damaged parts, such as misfolded proteins and worn-out mitochondria, the cell's power plants. Yoshinori Ohsumi won the 2016 Nobel Prize for discovering how this system works.
With age, autophagy tends to slow, which is one of the twelve hallmarks of aging, the main processes scientists agree drive aging. Two cellular switches control it: mTOR, the "grow" signal that turns it down when food is plentiful, and AMPK, the fuel gauge that turns it up when energy is low. That's why fasting and exercise both promote it.
A common myth
Autophagy switches on after exactly 16 hours of fasting.
In mice, autophagy rises clearly after 24 to 48 hours without food. In humans, nobody knows the exact timing, because it's very hard to measure in living people. The 16-hour number has no solid human study behind it.
Go deeper
Deep dives
- How long do you have to fast for autophagy? The honest answer
- Does coffee break a fast? It depends what you're fasting for
- mTOR and aging: the growth switch you want on, and off
Related terms
Updated Nov 9, 2026 · All terms