Healthy Friday: Fasting for 2 to 4 days can reboot your immune system

The study shows 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”.

The study

  • proves that not eating triggers stem cell-based regeneration of an organ or system
  • proves that the white blood cell counts of patients receiving chemotherapy, who did not eat for long periods, were lower
  • has major implications for healthier aging – the decline of the immune system as people age contributes to increased susceptibility to disease
  • proves that fasting for two to four days at a time over six months, kills older and damaged immune cells and generate new ones
  • has implications for chemotherapy tolerance and for those with a wide range of immune system deficiencies, including autoimmunity disorders


Valter Longo, Edna M. Jones Professor of Gerontology and the Biological Sciences at the USC Davis School of Gerontology and director of the USC Longevity Institute says: “We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system.”

“When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged. What we started noticing in both our human work and animal work is that the white blood cell count goes down with prolonged fasting. Then when you re-feed, the blood cells come back. So we started thinking, well, where does it come from?”

The effects of prolonged fasting on the body

  • Prolonged fasting forces the body to use stores of glucose, fat and ketones, but it also breaks down a significant portion of white blood cells. Longo likens the effect to lightening a plane of excess cargo.
  • During each cycle of fasting, this depletion of white blood cells induces changes that trigger stem cell-based regeneration of new immune system cells.
  • Prolonged fasting also lowered levels of IGF-1, a growth-factor hormone that Longo and others have linked to aging, tumour progression and cancer risk.

Fasting cycles can generate a new immune system

Longo says: “The good news is that the body got rid of the parts of the system that might be damaged or old, the inefficient parts, during the fasting. Now, if you start with a system heavily damaged by chemotherapy or aging, fasting cycles can generate, literally, a new immune system.

“We are investigating the possibility that these effects are applicable to many different systems and organs, not just the immune system,” said Longo, whose lab is in the process of conducting further research on controlled dietary interventions and stem cell regeneration.”

More clinical studies are needed, and any such dietary intervention should be undertaken only under the guidance of a physician.

Caxton Central

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