Autophagy (from Greek “self-eating”) is the cellular pathway for degrading and recycling damaged components. Autophagosomes wrap damaged proteins, misfolded aggregates, and dysfunctional organelles, fuse with lysosomes, and break them down — releasing amino acids for reuse. Yoshinori Ohsumi received the 2016 Nobel Prize in Physiology or Medicine for elucidating the molecular mechanisms of autophagy.
## Autophagy Declines With Age
Autophagic activity falls with age, and this decline contributes to multiple aging pathologies:
**Proteostasis**: autophagy clears misfolded protein aggregates including amyloid-β, α-synuclein, and tau. Its decline directly contributes to Alzheimer’s, Parkinson’s, and Huntington’s disease.
**Mitochondrial quality control**: mitophagy (selective mitochondrial autophagy) removes damaged mitochondria. Declining mitophagy contributes to the age-related mitochondrial dysfunction that reduces cellular energy output.
**Immune function**: autophagy participates in antigen presentation and pathogen clearance, partly explaining reduced immune competence in older people.
**Genetic evidence**: overexpressing autophagy genes (Atg5, TFEB) extends lifespan in C. elegans, Drosophila, and mice — direct causal evidence linking autophagy to longevity.
## Activating Autophagy
**Caloric restriction and fasting**: the most reliable autophagy activators. Energy deficit activates AMPK, inhibits mTOR, and initiates the autophagy program. After 12–16 hours of fasting, autophagic activity rises substantially.
**Exercise**: acute endurance exercise strongly activates autophagy in skeletal muscle, contributing to the well-established health benefits of physical activity.
**Rapamycin**: direct mTOR inhibition makes rapamycin the most potent pharmacological autophagy activator. See [Rapamycin and Longevity](https://sunqi.org/rapamycin-longevity-en/).
**Spermidine**: a natural polyamine abundant in whole grains, legumes, and mushrooms, activating autophagy by inhibiting the EP300 histone acetyltransferase. Epidemiological studies associate high spermidine dietary intake with lower cardiovascular mortality; human trials are underway.
**NAD⁺ precursors (NMN, NR)**: activate SIRT1, which promotes autophagy, contributing to the mechanism by which NAD⁺ supplementation may slow aging.
## Autophagy and Cancer
Autophagy is context-dependent in cancer: it protects normal cells but also allows tumor cells to survive nutrient deprivation. This dual role has driven both autophagy-activating and autophagy-inhibiting strategies in oncology. Chloroquine and hydroxychloroquine inhibit lysosomal acidification and are used in cancer autophagy-inhibition trials.
For context, see [Longevity Diet](https://sunqi.org/longevity-diet-caloric-restriction-en/) and the thorough review at [Nature Reviews Molecular Cell Biology](https://www.nature.com/articles/s41580-022-00541-z).
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