A new USC study showed that cycles of prolonged fasting not only protect against immune system damage — a major side effect of chemotherapy — but also induce immune system regeneration, shifting stem cells from a dormant state to a state of self-renewal.

Valter Longo

Corresponding author Valter Longo, PhD, Edna M. Jones Professor of Gerontology and the Biological Sciences at the USC Davis School of Gerontology and director of the USC Longevity Institute, said the work provides the first evidence of a natural intervention triggering stem cell-based regeneration of an organ or system.

The study appeared in the June 5 issue of the Cell Stem Cell.

In both mice and a Phase 1 human clinical trial, long periods of not eating significantly lowered white blood cell counts. In mice, fasting cycles then flipped a regenerative switch, changing the signaling pathways for hematopoietic stem cells, which are responsible for the generation of blood and immune systems, the research showed.

Longo, who has a joint appointment at the USC Dornsife College of Letters, Arts and Sciences, said the study has major implications for healthier aging, in which immune system decline contributes to increased susceptibility to disease as people age.

By outlining how prolonged fasting cycles — periods of no food for two to four days at a time over the course of six months — kill older and damaged immune cells and generate new ones, the research also has implications for chemotherapy tolerance and for those with a wide range of immune system deficiencies, including autoimmunity disorders.

Longo said, “We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system.”

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— Suzanne Wu