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 ...

An interesting paper on calorie restriction biochemistry via PubMed: ''Both life-long caloric restriction (CR) and the suppression of insulin-like growth factor-1 (IGF-1) signaling reliably extend the mammalian lifespan. The neuroendocrine system, regulated by the hypothalamus, remains the most convincing site of action for both these modes of ...