I have fasted in the past and my weight stayed down a long time after fasting following a low fat vegan diet, it only went back up when I went of that diet and started eating fatty processed foods again.
I found I got full easier after fasting making bingeing hard. I was eating a lot of fruits, vegetable stews. My weight stayed down.
Fasting does slow down your metabolism but for a few weeks, it's not permanent, unless maybe if you are anorexic and never eat anyway.