I wrote this awhile ago, regarding Fung Fasting. This is just my opinion. 36 hour fasts are something that I have done off and on since I was in my early to mid twenties.
FUNG FASTING - MY OPINION:
I struggled with my weight by age 8, trying many many diets along the way. I lost bits here and there with periodic extreme dieting, as regular weight loss programs such as Weight Watchers and the like, would result in such slow losses that I'd become discouraged from the get go. (Unlike most, my first week of any diet would help me lose 1/2-1 lb.)
In my early 20's, out of desperation, I dabbled in fasting 36+ hours at a stretch, so after approximately 8 years of periodic extreme dieting and fasting episodes, my total weight lost was 60 lbs. My metabolism was at a new record low, allowing me only 1000 calories per day for maintenance, which I eventually couldn't hold any longer.
We are all different, but for those that do not have health issues such as Dr. Fung deals with, complete fasting may do more harm than good on their metabolism.
I do not have a normal metabolism, never have, never will. For me, complete fasting lowers my metabolic rate. It did when I was in my 20's and again recently when I did a 3 week stint of 42 hour fasts when Dr. Fung's book "The Obesity Code" hit the bookshelves. While I appreciate his wisdom, for me, the fasting aspect did me more harm than good. Complete fasting didn't improve my metabolism in my 20's, so I should have known better than to try it in my 50's. 
I'm working on improving my metabolism at present, going back to the basics that serve me well.
JUDDD
JUDDD
Note: One last thing to keep your eyes out for are those who are now in maintenance following Fung Fasting. What is their metabolism like afterward? Fung Fasting put me into one of two plateaus. If we end up with a lesser metabolism, is it worth it, even if we lose weight quickly? We need to quit looking at weight loss with a microscope. Instead, see it as a telescope and look at the long term harm possible effects.
