Fasting has multiple metabolic and cellular impacts. As another commenter noted fasting triggers autophagy (self eating) where cells use parts/proteins from de

Fasting has multiple metabolic and cellular impacts. As another commenter noted fasting triggers autophagy (self eating) where cells use parts/proteins from dead cells to repair themselves. The research and work done in this field won a Nobel prize. As you note cells constantly die and are replaced but this replication is where a lot of poor genetic code can get copied into the new cells. One of the interesting things about autophagy is that through cellular repair cells actually live longer and don’t need to be replaced as often, this longevity and health of the cells appears to result in overall longevity and health of the subject.