AI says: A 72-hour fast may positively impact the immune system by triggering a regeneration process, potentially leading to the breakdown of old and damaged immune cells and the production of new ones. This process, known as autophagy, involves the body using its own cells for energy during fasting, which can lead to a reduced inflammatory response. Some research suggests that a 72-hour fast can also help protect against the damaging effects of chemotherapy on the immune system.