How is autophagy activated?

Autophagy is activated when the cells of the body are deprived of essential oxygen or nutrients if they are damaged in any way. Autophagy is essentially a recycling process in which dysfunctional cells are broken down into their individual components, which are then recycled for reuse. This recycling process makes the most of the energy resources already existing in the cell. 

When the cells do not get the oxygen and nutrients they need from an outside source such as during starvation, autophagy gets activated to allow the body to make the most of the resources it already has.