Caloric restriction and longevity: the science and the ascetic experience.

Aging involves a gradual increase in disorder of the systems that sustain living. Although stress is a major driver of this process, one stressor, caloric restriction (CR), is the only intervention proven to extend life span in multiple species as well as extend the persistence of those characteristics that are associated with youth. CR has been used since ancient times to enhance many of those characteristics: principally, increased activity levels and heightened levels of mental acuity. Religious ascetics, often living in monastic communities, have provided long-term opportunities to observe the effects of CR, or fasting, in humans. Tibetan medicine has made use of observations, which include that of enhanced immune function, in its dietary prescriptions. In the hopes of reaping these benefits for the general population, scientists focusing their research on the aging process have sought mimetics that will deliver the benefits of CR without requiring the discipline of fasting. The search begins with discovering the processes that make CR work.