From this article in Medical News Today, Prolonged fasting re-boots immune system, come these quotes:
“Results of a new study on mice and a phase 1 trial of humans suggest that prolonged cycles of fasting - for 2-4 days at a time - not only protect against toxic effects of chemotherapy, but also trigger stem cell regeneration of new immune cells and clearing out of old, damaged cells.”
“The scientists say prolonged fasting appears to shift stem cells of the immune system from a dormant state to an active state of self-renewal.”
“When you stop eating, the body uses up stored glucose, fat and ketones, and also recycles worn out and damaged immune cells.”
This study was conducted on mice. This result is preliminary and more studies are needed with humans. The article cautions that this fasting should be done under medical supervision.