Dietary restriction, tumors, and aging in rodents.

A chronic 30-50% restriction of dietary energy intake (but without malnutrition) typically and strongly lowers the incidence of most spontaneous and induced tumors, delays their onsets, and extends maximum life span in rodents. When compared to normally fed controls, animals fed these dietary restriction (DR) regimens show decreased rates of change for most (but not all) age-sensitive biologic indexes studied to date. DR's impact on chemically induced tumors appears to depend more on energy than on fat restriction, and result from less promotion (and not less initiation). The molecular and cellular events underlying these various outcomes of DR are unclear. Viable explanations include less cellular oxidative damage, a retardation in the age-related changes in the immune system, hormonal changes, less exposure to dietary carcinogens and promoters, less energy for tumor growth, less carcinogen activation, and better DNA repair. New findings are consistent with the notion that DR reduces cellular damage mediated by active oxygen. A lower production or higher detoxification rate of active oxygen species, which damages molecules and promotes tumor growth, could explain DR's effects on aging and tumors.