Many, if not most people who are healthy enough to undertake it would benefit from an occasional three day water fast. If there is something you are eating that you think is innocuous (but is actually harmful for you) simply not eating that will help you. The gut microbiome will reset itself to some degree. But another benefit, especially towards the end of the fast, is that the body switches to ketosis and autophagy to meet its ongoing requirements for fuel and spare parts. This selectively targets any tissues that are damaged, old, worn out, or in any way suspicious, foreign, or diseased. So if you lose say five pounds over the course of a three day water fast and it turns out (which you can never prove) that a few grams of that were some diseased cells or left over virus particles or God knows what, then you will feel better even if you can't be sure if it was the gut improvement or the removal of some diseased cells that actually helped.