Actually, not eating for an extended period does have one very significant effect. It radically changes the makeup of your microbiome. I suspect that people who experience health benefits from "detoxes" typically suffer from dysbiosis, and by restricting food supply they essentially hit the "reset" button on their gut bacterial populations.
...and then the bacteria reverts to previous within a few days of returning to the previous diet. Gut bacteria adapts really rapidly to whatever you're eating, whether you do a "reset" in between or not.
Well, probably, but that is not absolutely certain. Sometimes, after a forest fire, the types of trees that end up dominating are different from the trees that dominated before the fire.
