We know that calorie restriction (CR) greatly improves insulin sensitivity - which seems to be one of the ways in which it increases life span - just as eating too much and getting fat tends to lead to insulin resistance and the diabetes that follows. Here, researchers are making slow inroads into understanding why CR does this: "Caloric restriction (CR) has been shown to retard aging processes, extend maximal life span, and consistently increase insulin action in experimental animals. The mechanism by which CR enhances insulin action, specifically in higher species, is not precisely known. We sought to examine insulin receptor signaling and transcriptional alterations in skeletal muscle of nonhuman primates subjected to caloric restriction over a 4 year period. ... CR increases insulin sensitivity on a whole body level and enhances insulin receptor signaling in this higher species. CR in cynomolgus monkeys may alter insulin signaling in vivo by modulating protein content of insulin receptor signaling proteins."

Link: http://www.ncbi.nlm.nih.gov/pubmed/19336678