Calorie restriction (CR) (reduced calories with adequate nutrition) in multiple organisms increase mean and maximum lifespan. The big question (along with CR mimetics) is will it do the same in humans?
One mechanism (of many) that is thought to be involved in CR effect on lifespan is the lowering of IGF-1. It was an open question of does CR reduce IGF-1 in humans. Now we know the answer, CR by itself does not appear to reduce IGF-1 levels in humans. However, strict vegans do have lower levels which researchers thought might be tied in to their low consumption of protein (10%) (as people on CR consume over 20%). They next found convinced serveral humans following CR to reduce their protein levels to the same level and found IGF-1 levels were reduced. Interestingly, Ouroboros recently covered the potential use of vegetarian diet instead of CR because it might be easier to follow that CR.
thanks to all the following sources (and for further coverage click away).
But remember IGF-1 pathway is only one of a number of pathways (and ever growing it seems) that is altered with CR and therefore not having the same effect between mice and humans for this one pathway does not answer if CR will have a longevity effect in humans.