EFFECTS OF DIETARY RESTRICTION AND EXERCISE ON THE AGE-RELATED PATHOLOGY OF THE RAT

Intervention of the aging process is an effective, experimental means of uncovering the bases of aging. The most efficacious and commonly us ed intervention used to retard the aging processes is dietary restrict ion (DR). It increases mean and maximum life spans, delays the appeara nce, frequency, and severity of many age-related diseases, and more im portantly, attenuates much of the physiological decline associated wit h age. Although the subject of intense research, the mechanism by whic h DR alters the aging processes is still unknown. Physical exercise is another effective intervention shown to affect aging phenomena, espec ially when applied in combination with DR. Mild exercise in concert wi th DR is beneficial, but vigorous exercise coupled with DR could be de leterious. With regard to pathology, exercise generally exerts a salut ary influence on age-related diseases, both neoplastic and non-neoplas tic, and this effect may contribute to the increase in median life spa n seen with exercised rats. Exercise coupled with 40% DR was found to suppress the incidence of fatal neoplastic disease compared to the sed entary DR group. Exercise with mild DR suppressed the incidence of mul tiple fatal disease and chronic nephropathy, and also delayed the occu rrence of many age-related lesions compared to the ad libitum (AL) con trol group. However, these effects may have little bearing on the agin g process per se, as maximum life span is only minimally affected. Alt hough not as intensively studied as DR, results from studies that util ize exercise as a research probe, either alone or in combination with DR, have helped to assess the validity of proposed mechanisms for DR a nd aging itself. Neither the retardation of growth rate nor the increa se in physical activity, observed with either exercise or DR, appear t o contribute to the anti-aging action of DR. Moreover, results from li felong exercise studies indicate that the effects of DR do not depend upon changes in energy availability or metabolic rate. The mechanisms involving effects on adiposity or immune function are also inadequate explanations for the action of DR on aging. Of the proposed mechanisms , only one, as postulated by the Oxidative Stress Hypothesis of Aging, tenably accounts for the known effects of DR and exercise on aging.