Reducing the amount of nutrients available to a cell seems to trigger a group of innate pathways that enhance the cell’s stress resistance and metabolic efficiency—all of them related, in some way, to mTOR. The first of these is an enzyme called AMP-activated protein kinase, or AMPK for short. AMPK is like the low-fuel light on the dashboard of your car: when it senses low levels of nutrients (fuel), it activates, triggering a cascade of actions. While this typically happens as a response to lack of nutrients, AMPK is also activated when we exercise, responding to the transient drop in
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