Jun 08, 2014 08:42 PM EDT By Jaleesa Baulkman, UniversityHerald Reporter

Fasting for at least three days could rejuvenate the entire immune system, even in elderly, according to a recent study The Telegraph reported.

Researchers from the University of Southern California found 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.

"We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system," Valter Longo, corresponding author of the study and  the Edna M. Jones Professor of Gerontology and the Biological Sciences at the USC Davis School of Gerontology, said in a statement. "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."

The researchers said prolonged fasting forces the body to use stores of glucose, fat and ketones, but also breaks down a significant portion of white blood cells. Longo likens the effect to lightening a plane of excess cargo.

They also found that prolonged fasting also reduced the enzyme PKA, which is linked to ageing and a hormone which increases cancer risk and tumor growth.

"PKA is the key gene that needs to shut down in order for these stem cells to switch into regenerative mode. It gives the 'okay' for stem cells to go ahead and begin proliferating and rebuild the entire system," Long said. "And 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."

During a trial, prolonged fasting also protected against toxicity in a pilot clinical trial in which a small group of patients fasted for a 72-hour period prior to chemotherapy.

"While chemotherapy saves lives, it causes significant collateral damage to the immune system. The results of this study suggest that fasting may mitigate some of the harmful effects of chemotherapy," Tanya Dorff, co-author of the study and an assistant professor of clinical medicine at the USC Norris Comprehensive Cancer Center and Hospital, said in a statement.

Researchers are now investigating the possibility that these effects are applicable to many different systems and organs, not just the immune system.

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