I forgot to answer here. Personally I have found that heavy calory restrictive diets tend to confuse the body. Are you eating or fasting? Which mode should it pick? As a result it never enters fasting mode, leading to more muscle loss. Not to mention constant craving for food.
I’m not worried about metabolic slowdown. Most of the metabolism is linked to the musculoskeletal system, so as long as you have muscles and strong bones, your BMR can not go below a certain point. Although after a few weeks the body will go into a form of power-saving mode much like a computer, where it slows down everything and you need to move around for a bit for everything to reach maximum speed again.
I remember when I did a dry fast. After three days without water it took me about 20 minutes to get back to “normal” after waking up. For those first 20 minutes I looked like a senior citizen with a walking aid. But I could literally feel things slowly revving up inside my body, gaining speed until everything was running well again.
And YES, a human body can survive without water for longer than 3 days (I lasted 5), as long as you don’t eat either. Up to 14 days actually, provided the air has a high humidity so the skin and lungs can absorb some water, distilling the rest it needs from burning fat and anything else that’s wrong with the body. Including tumors, according to Dr. Filonov’s research. Don’t expect to be very active after day 2 though.
When it comes to the calory restriction diets, I believe the 5:2 diet is quite successful. Which is essentially doing those 500 calories 2 days a week and eating normally the rest of the week.
I still prefer Brad Pilon’s Eat Stop Eat method of doing a 24 hour fast once or twice a week. Maybe it’s because I’m lazy and don’t want to have to think about things. I never got into juice fasting because I really didn’t want to clean the juicer after every drink. 
Another one I know works is ADF (Alternate Day Fasting). There’s a YouTube channel of a girl that did that for a year I believe and ended up losing pretty much all the excess weight.
Of course, combine any of the above methods with 16:8 or even OMAD (One Meal a Day or 23:1) and you’re golden.
Completely unrelated, but what is the singular of calories? Does it even exist? Calory never makes it through the spellcheck.
