Scientists have been studying the effect on the body's metabolism of fasting, and how it may play into aging. In this web exclusive, "Sunday Morning" correspondent Lee Cowan talks with three researchers on aging – David Sinclair, of Harvard Medical School; Dr. Nir Barzilai, of the Albert Einstein College of Medicine; and Morgan Levine, of the Yale Center for Research on Aging – about the stresses on the body by fasting or caloric restriction, and how it may turn on the body's defenses against aging.