Sometimes a cell needs to break down its own parts. The process is called autophagy. The term comes from a Greek word that means “self-devouring.” During autophagy, the cell parts to be recycled get isolated in a small sac called an autophagosome. This sac fuses with another sac filled with enzymes. The enzymes break down the junk parts. Those broken down bits can then be used again. Sometimes cells use autophagy when they are starving, eating bits of themselves to keep their energy levels up. Autophagy is thus important in exercise, but it’s also been shown to play a role in cancer and Parkinson’s disease.