Does fasting help your cells clean themselves up?

Fasting is the most powerful non-genetic way to activate autophagy, the self-cleaning function of your cells. This applies to a wide range of tissues and organs, and has been demonstrated in both animal research and in humans.

An important part of the mechanism is spermidine, a substance your body produces on its own. When you fast, spermidine levels rise, and this rise occurs across multiple types of organisms, including humans. If that spermidine production is blocked, the cleansing effect of fasting largely disappears. Spermidine therefore appears to be an indispensable link in the chain.

Fasting also activates the removal of damaged mitochondria (the powerhouses of your cells) in muscles. There is, however, a downside to this: the same cleanup pathway is associated with muscle breakdown. Anyone who fasts regularly and wants to preserve muscle mass would be wise to keep a close eye on this, for example by eating enough protein and doing strength training.

An early eating window, in which you stop eating as early as 14:00, increased the activity of an autophagy gene in a small study involving 11 people. That outcome is interesting, but the study was too small and too short to draw firm conclusions from.

Fasting therefore has a clearly demonstrable effect on cellular cleanup, but larger randomised trials in humans are still needed to confirm the precise magnitude and long-term effects. The risk of muscle breakdown during prolonged or intensive fasting is a concrete downside that should not be underestimated.