The body destroying its own cells may not sound like a good thing. But autophagy is a natural defence that our bodies use to survive.
It allows the body to cope with starvation and fight off invading bacteria and viruses, for example.
And it clears away old junk to make way for new cells.
Failure of autophagy is linked with many diseases of old age, including dementia.
Research is now ongoing to develop drugs that can target autophagy in various diseases, including cancer.
The concept of autophagy has been known for over 50 years, but it wasn't until Dr Ohsumi began studying and experimenting with baker's yeast in the 80s and 90s that the breakthrough in understanding was made.
Dr Ohsumi is reported to be surprised about receiving his Nobel Prize, but "extremely honoured".