Research shows a 72-hour fast can completely rebuild your immune system. A study from the University of Southern California has revealed that fasting for 72 hours can trigger a complete regeneration of the immune system. Researchers found that prolonged fasting causes the body to deplete its glucose and fat reserves, forcing it into a detoxifying state that eliminates damaged cells and toxins. When normal eating resumes, stem cells are activated, leading to the production of fresh, healthy white blood cells. This immune reboot effect was observed in both mice and humans, particularly in chemotherapy patients who showed improved immune health after fasting cycles. Lead researcher Dr. Valter Longo explains that during fasting, a gene called PKA is suppressed—this gene must be turned off for stem cells to enter regenerative mode. As a result, the immune system essentially clears out older, weaker components and rebuilds itself anew. While more research is needed to explore the full range of benefits across organs, the study suggests that fasting could be a powerful, drug-free strategy for enhancing immunity, especially for those with weakened systems due to aging or cancer treatment. [Valter Longo. USC Leonard Davis School]