Caloric Restriction and Aging: Eat Less, Live Longer
Caloric restriction (CR), which is defined as undernutrition without malnutrition, is the only experimental manipulation known to retard aging and increase survival of mammals. CR has been shown in repeated experiments to extend mean and maximum life span, decelerate the rate of aging, and inhibit the onset of a number of life-shortening diseases in laboratory animals. The complete mechanism of how CR produces these beneficial changes is not understood, but pathological and molecular observations have provided much information on the ways in which CR decelerates aging. The first theory is the reduction of oxidative damage to tissues. Free radical production damages tissues and produces many effects of aging. Antioxidants that are produced in youth decline with age and do not provide as complete protective effects. However, it was found that CR maintains youthful levels of many antioxidants and in this way, aids in the prevention of aging. CR also elevates Hsp70, a heat shock protein that responds to pathological and environmental stresses like hyperthermia and ischemia. All living organisms show a reduced ability to respond to stress as they age which can be correlated to a decrease in heat shock protein transcription and expression. CR maintains youthful levels of HSP70 and perhaps via this mechanism, preserves the integrity of body and organs in response to stress. Another hypothesis is that CR extends life span by altering body metabolism and thereby decreasing the deposition of pathological fat in the body. Finally, CR is believed to prevent carcinogenesis by increasing apoptotic rates. Though these hypothesis are well supported, much more work must be done to get a complete picture of how CR extends life and inhibits aging. However, based on the strong evidence that CR reduces life-threatening disease and extends life, it would be a wise suggestion that we all practice moderation in our caloric intake.