We’ll forgive you if you find this a bit unbelievable, but here it is: fasting in excess of seventy-two hours can help trigger stem cell regeneration of the immune system. It’s a pretty big deal.
The study, published in Cell Stem Cell, is the first to show natural intervention (i.e., the fasting) triggering stem cell-based regeneration of an organ or system. Even the authors were surprised. According to author Valter Longo, “We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system.”
In both mice and a human trial, completely abstaining from food for two to four days at a time over a course of six months caused the body to kill old and damaged white blood cells. Prolong fasting causes the body to get rid of glucose, fat, and ketones to save energy, but when the body starts getting rid of white blood cells, it’s the least helpful ones that go first. Then, when subjects started eating again, the body produces new white blood cells, effectively replacing the old and damaged with the new and perfect.
Though the people involved with this study were undergoing chemotherapy, don’t expect to see your doctor recommending a course of fasting for awhile. That said, if the idea of intermittent fasting is interesting to you, check out the excellent fitness book Man 2.0: Engineering the Alpha.