I agree with July. Most of us are gluten/dairy/sugar/processed free. You can't gain weight when eating only real foods.
Hunger is dictated by nutrients, not calories. Since most of us eat real, unprocessed, highly plant based diets, we are getting the nutrients we need. Hopefully we are absorbing them.
I cannot imagine doing a 21 day water cleanse and still being alive at the end.
I hope you aren't considering that
I do think diet plays a big role in healing/helping immunity. But I have always thought that and we all have moments when we go off and we get more inflammation or don't feel well.