I've heard a talk recently by a guy who works with scientists who do calorie restriction experiments.

What he said is an eye-opener. The animals look healthier but they don't live longer. They don't seem to die of age, but they do just drop dead one day, not always from any obvious cause at all - although they seem particularly susceptible to infections.

His hypothesis was that calorie restriction works by forcing the body on such low resources it has to cannibalize itself, which has the advantage it cleans up age-related crud much more effectively - and the disadvantage that there is absolutely no slack in the system. Every problem is a crisis.