I did a ridiculously long fast for the purpose of weight loss. Did my metabolism slow down? I'm sure it did, temporarily. I regained 10 whole pounds when I started eating again. Fortunately I had lost over 100 pounds so the 10 pounds regained didn't bug me so much. My metabolism was definitely not ruined either and has increased as I built muscle mass.
Plus... Durian Rider is absolutely insane. ; )