More On IGF-1 and Calorie Restriction
Calorie restriction (or rather protein restriction in this case - there is a difference) is linked with reduced levels of insulin-like growth factor-1 (IGF-1): "people on a low-protein, low-calorie diet had considerably lower levels of a particular plasma growth factor called IGF-1 than equally lean endurance runners ... That suggests to us that a diet lower in protein may have a greater protective effect against cancer than endurance exercise, independently of body fat mass. ... Past research has linked pre-menopausal breast cancer, prostate cancer and certain types of colon cancer to high levels of IGF-1, a powerful growth factor that promotes cell proliferation. Data from animal studies also suggest that lower IGF-1 levels are associated with maximal lifespan." Some commenters feel that the study didn't control enough of the other variables to make any strong suggestion, but the evidence is piling up.