The present scientific consensus on calorie restriction in humans is that it will do wonderful things for your health and resistance to age-related disease, but won't extend the maximum human life span to the same degree that is seen in lower animals: "In the majority of the animal models of longevity, extended lifespan involves pathways related to a growth factor called IGF-1 (insulin-like growth factor-1) ... In calorie-restricted animals, levels of circulating IGF-1 decline between 30 percent and 40 percent. ... We looked at IGF-1 in humans doing calorie restriction [and] found no difference in IGF-1 levels between people on calorie restriction and those who are not. ... we know there are two major influences on IGF-1 levels: calorie intake and protein intake. So we decided to look at the influence of protein ... six [human testers] agreed to lower their protein intake and after three weeks their circulating IGF-1 declined dramatically ... It's much easier to restrict protein than to restrict calories. If our research is on the right track, maybe humans don't need to be so calorie restricted. Limiting protein intake to .7 or .8 grams per kilogram per day might be more effective. That's just a hypothesis. We have to confirm it in future studies."

Link: http://www.sciencedaily.com/releases/2008/09/080924151018.htm