Much has been made of the research into calorie suppression and the apparent benefits for an increased lifespan. Thus far we have no data in humans (research is currently underway) but we have seen benefits in fruit flies, worms, and mice. More specifically we can see that this effect on longevity can be attributed to protein restriction, in particular methionine.
Mechanistically the understanding is that this would be due to suppression of MTOR which signals to the body the need for construction of new tissue. When MTOR is away, its' antagonist, AMPK, will play. AMPK is the master regulator of the fasted state and reacts to this depressed energy availability by signalling for a focus on repairing currently damaged tissues which could explain the benefit to longevity.
Autotophagy is another process regulated by AMPK and describes the important cellular house cleaning of the body which breaks down damaged proteins and repairs cellular structures to ensure optimal function.
However, while it is obvious that simple organisms such as fruit flies and worms probably don't say much about the human body, we should also be cautious in drawing conclusions from results in mice. Their lifespan is just 24 months, as compared to a human's ~80 years, and the energy expenditure rate per unit of body mass is 7 times that of humans. Taking this into account it would make sense that the longevity effects would be far larger than what we could expect in humans.
As well as acknowledging the need for more evidence, we must also recognise that even if we would expect to see the same results in humans as in mice we are really only talking about an extra 5 years at best. Given the myriad benefits of a higher protein diet for muscle mass, satiety, thermogenesis, body composition, and sarcopenia, would you trade the quality of your last 30 years os life for an extra, crappier, 5 years? The vast majority of people would not.
We needn’t give up completely though, as the benefits of autophagy could likely be achieved while eating a high protein diet if the food is consumed within an 8-12 hour window. As we learn more we will probably attain a better understanding of how the positive health effects of a high protein diet can be achieved while also negating or suppressing the negatives.