Fasting for improved health

For me, the whole dichotomy of what's good and what's bad for the goodies and the baddies, is a whole big mind blow.  We in this most wundebar club have in our bodies (or had in our bodies) both good and bad cells. If such and such wonderfood is going to strengthen the good cells in order to fight the bad cells, how do we know that the tables won't be turned, and the bad f***ers munch all the wonder grub and fight the goodies with renewed vigour? As for this modern day fixation with X amount of water to be glugged by the litre...why? According to this theory that tea and coffee dehydrate you, and that if you drink 200 ml, you will pee that much and more and will thus dehydrate. To offset this condition, you have to drink blah blah amount of water over and above the water in said devil drinks, food, milk, cold drinks and so on. Well bugger me...I should be a stick of dry biltong (jerky) by now as I loathe water by itself. So far, I've lived in a state of chronic dehydration for 60 years. My unschooled mind says to me that one would need all the nutrition and hydration that your body can get to fight back. It makes no sense to me that a body under stress by being starved of all the nutrients it needs at times like this, would be better off. But, as I've said...I'm just a frumpy old housewife, not a specialist oncologist. At least I'm not a snake oil salesman, flogging false hope.