In short
AMPK (AMP-activated protein kinase) is an enzyme that acts as the cell's energy sensor, activating when ATP is low relative to AMP and triggering processes that restore energy balance, including autophagy.
Every cell needs a way to detect when it is running low on usable energy. AMPK does this by sensing the ratio of AMP to ATP — when energy is scarce, AMP rises, AMPK activates, and it flips a broad set of switches: it turns on fatty acid oxidation and glucose uptake to generate more ATP, it promotes mitochondrial biogenesis (making more mitochondria), and it activates autophagy while suppressing mTOR, the growth-promoting pathway that dominates when energy is abundant.
Exercise, fasting, and caloric restriction are the most well-established physiological activators of AMPK in humans — muscle contraction and energy deficit both raise the AMP:ATP ratio. The diabetes drug metformin also activates AMPK, indirectly, by mildly inhibiting mitochondrial complex I, which is one of the proposed mechanisms behind interest in metformin as a longevity compound (alongside effects that are independent of AMPK).
AMPK activation is considered one of the more plausible convergence points between exercise, fasting, and some pharmacological interventions studied in aging biology, largely because it opposes mTOR and promotes autophagy — but AMPK's role in human longevity is inferred from its position in this network, not demonstrated by a trial showing that AMPK activation itself extends human lifespan.
Worth remembering
- Senses low cellular energy (high AMP:ATP) and restores balance.
- Activated by exercise, fasting, and caloric restriction; also by metformin.
- Opposes mTOR and promotes autophagy and mitochondrial biogenesis.