Here is where I am confused.

the amount of energy actually required by the human body to survive, is I would say, surprisingly less than most would imagine.

One of the videos that is in one of your earlier posts on day 2 states that fasting increases the basal metabolic rate of the body but you are saying that it slows it down. Which one is it?

It also says that Leucine is increased in fasting which allows muscles to bulk but where is that Leucine coming from since it is classified as a essential amino acid meaning that mammals can't produce it. Is it the person's microbiome stepping up production in response to the lack of food? If so what are they using as fuel?

I believe that on a fast there are many sources of which your body is pulling energy from

What are these other sources that you mention? If it is your internal organs you could quickly have a problem.