It is widely held that caloric restriction (CR) extends lifespan by preventing or reducing the age-related accumulation of irreversible molecular damage. In contrast, our results suggest that CR can act rapidly to begin life and health span extension, and that its rapid genomic effects are closely linked to its health effects. We found that CR begins to extend lifespan and reduce cancer as a cause of death within 8 weeks in older mice, apparently by reducing the rate of tumor growth. Further, 8 weeks of CR progressively reproduces nearly three quarters of the genomic effects of long-term CR (LTCR) in liver. Fewer of the genomic effects of LTCR are rapidly reproduced by the initiation of CR in the heart, but the changes produced are keys to cardiovascular health. Thus, the genomic effects of CR may be established more rapidly in mitotic than in postmitotic tissues. Most of the genomic effects of LTCR dissipate 8 weeks after switching to a control diet. Consistent with these results, others have shown that acute CR rapidly and reversibly reduces the short-term risk of death in Drosophila to that of LTCR treated flies. Further, in late adulthood, acute CR partially or completely reverses age-related alterations of liver, brain and heart proteins. CR also rapidly and reversibly mitigates biomarkers of aging in adult rhesus macaques and humans. These data argue that highly conserved mechanisms for the rapid and reversible enhancement of life- and health-span exist for mitotic and postmitotic tissues.