Corresponding author Valter Longo of the University of Southern California Davis School of Gerontology and director of the USC Longevity Institute, said in both mice and a Phase 1 human clinical trial, long periods of not eating considerably lowered white blood cell counts.
The study, published in the journal Cell Stem Cell, found in mice fasting cycles "flipped a regenerative switch" changing the pathways for hematopoietic stem cells, which are responsible for the generation of blood and immune systems.
"We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system," Longo 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. 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."
Prolonged fasting forces the body to use stores of glucose, fat and ketones, and breaks down a large portion of white blood cells. Longo described the effect as jettisoning a plane of excess cargo.
In addition, the fasting reduced the enzyme PKA linked to the regulation of stem cell self-renewal and pluripotency -- or the potential for one cell to develop into many different cell types. It also lowered levels of IGF-1, a growth-factor hormone that has been linked to aging, tumor progression and cancer risk.
In a pilot clinical trial, a small group of patients fasted for a 72-hour period before their chemotherapy and it might have helped protect against the toxicity of the cancer drugs' side effects.
"While chemotherapy saves lives, it causes significant collateral damage to the immune system," said study co-author Tanya Dorff of the USC Norris Comprehensive Cancer Center."The results of this study suggest that fasting might mitigate some of the harmful effects of chemotherapy. However, more clinical studies are needed, and any such dietary intervention should be undertaken only under the guidance of a physician."