Filanov said in one of his youtube interview that Dunning has no idea what he is talking about, and doubted he had ever done a long dry fast. I don’t trust him, or anyone that’s new-agey and selling immortality. Water fasts are safe if done properly.
In my opinion, I look at it as a “pure water fast is damaging to the heart/body” Especially an organ that runs off of electric impulses, constantly flushing out needed electrolytes will cause a weakened heart and heart arrhythmia. Dry fasting shown in multiple studies keeps your electrolytes very stable throughout the fast. This being due to hormones like vassopressin and other fsctors that are heigtened due to the fast. While a salt water fast with sodium+potassium is going to replenish and top off what you already have allowing you to exert yourself more during a fasting period.
Many Factors at play. If its a pure water fast with no electrolytes then maybe the individual risks something. Either way its a form of hormetic stress that the body is adapts to and how someone has treated themselves prior, combined with genetics, prep and post post fast dictates their bodies response