What is mTOR?
Mechanistic target of rapamycin
mTOR is a protein that acts as your cells' master growth switch: when nutrients are plentiful, it tells cells to build and grow; when it's quiet, they repair and recycle.
Think of mTOR as a construction foreman. When building materials arrive, he shouts "build!" When deliveries stop, crews switch to cleaning up and fixing what's already there.
Why it matters for aging
mTOR reads the cell's environment: nutrients like protein and sugar, insulin (the "food is here" hormone) and energy levels. When all say "plenty", mTOR switches on protein building and cell growth and switches off autophagy, the cell's recycling system.
The name comes from rapamycin, the drug that led to its discovery. In mice, turning mTOR down with rapamycin extended lifespan even when started late in life, which made it one of the most studied targets in aging research.
A common myth
mTOR is bad and should be kept as low as possible.
mTOR is essential for building muscle, healing and immunity. The problem is a switch that's always on. A healthy rhythm, with growth signals after exercise and meals and quiet periods in between, matters more than keeping it low.
Go deeper
Deep dives
- mTOR and aging: the growth switch you want on, and off
- How long do you have to fast for autophagy? The honest answer
Related terms
Updated Nov 9, 2026 · All terms