Scientists don't exactly know yet why calorie restriction extends lifespan of many animals. It's believed by many that a diet or calorie restriction adjusts the metabolism and physiology of an organism from the cellular level.
Less free radical damage, down regulate expression of IGF-1/mTOR, and a few others things I believe are known. I'm sure we are only touching the surface of it regardless.
Being able to manipulate the autophagy process can lead to scientific breakthrough to cure diseases
You can with fasting, and has already shown to be successful in cancer treatment and prevention - https://www.canceractive.com/cancer-active-page-link.aspx?n=3408
Sirtuin
Right...those proteins are naturally expressed via caloric restriction/fasting.
generally regarded as the means for life extension benefits of caloric restriction/fasting, and stimulate autophagy ;), remember exercise too. Nad+.