During the 3rd or 4th day of a water only fast your body detects that you are unable or unwilling to give it any new nutrition… so it shifts into survival mode, making numerous chemical changes. Ghrelin production is greatly reduced to reduce your hunger pangs dramatically. You will be almost hunger free for an extended period of time. Ghrelin production will resume only when you start eating food again.
I know that based on my personal research and my extensive extended fasting experiences. By day 4 I enter the hunger free zone whenever i do my quarterly 14 day fasts.