Well, both, but I do think it positively impacts longevity because the fast is for a reason much deeper than extending life. The main goal of fasting is to increase the intensity of prayer, but, it has many other benefits. And then after the fast there is the feast. All of this also happens in a trusted community, no one is alone.
My point is that fasting, at least in this blue zone, isn't an end unto itself. It's just one part of a way of life, so, to focus the diet misses the whole picture.