Hi Jean-Louis!!
  Thanks for this great letter!  I have some thoughts.

You write:
<<  --Myth 1: when you fast, after a few days, you have more energy. You can
<<walk  20 miles/day, run longer, etc.

Ten years ago I knew nothing about fasting at all, except I had (tried) to
read "The Science and Fine Art of Fasting" by Shelton (thumbed through and
read spots), "Rational Fasting" by Arnold Ehret and "The Miracle of Fasting"
by Paul Bragg (both of which I read in entirety). Those were the only books I
had ever come across anywhere that dealt with the subject.  It must have been
one of those that told stories about men accomplishing incredible physical
feats during extremely long fasts, out-running younger, fit, eating men, etc.
 So I never understood the concept of fasting being a period of rest, and I
figured I would have tons of energy. And - amazing and puzzling to me now - I
did!!  I remember doing one 15-day fast while running my usual 6 miles per
day, and organizing and  leading a huge three-day workshop that involved
finding people places to sleep all over town, organizing huge meals,
preparing and leading groups,  etc. - the kind of thing that is usually
extremely exhausting to anyone.  Other than losing my voice a little from
talking so much, I felt great and energetic through it all. And no one ever
knew I was fasting.

Today, the 7th day of my current fast, I have all I can do to go up a flight
of steps without stopping to pant in the middle, and other than trips into my
office to read email, I am spending all day everyday in bed, feeling very,
very, very weak and physically tired.

Is this because I now understand that I should be resting for maximum
benefit, so I'm paying attention to my body instead of overriding its needs
with my mind? Who knows!!

You write:
<<  Dark urine may result from autolysis (I'm not sure): your body uses its
muscle protein to fulfill its daily requirements in protein and glucose. But
after a few days, as the metabolism slows down and the nervous system
utilizes more fat instead of glucose, the rate of muscle loss is lower. >>

My understanding is that the body uses glucose available in the blood during
the first day, until it is depleted (very quickly). Then it goes to glycogen
stores to extract glucose there (stored in muscle tissue - thus resulting in
loss of protein and muscle mass). The body does not "want" to waste muscle
tissue this way, so when still no glucose is coming in from food, it then
resorts to another mechanism (gluconeogenisis) where it "cumbersomely"
synthesizes glucose from compounds in the liver. But by the 3rd-5th day the
body has converted to another ATP production system, ketosis, where it is
able to synthesize and use ketones from the fat stores rather than glucose.
 And in addition it extracts and uses whatever is usable from autolysis of
(HOPEFULLY HOPEFULLY HOPEFULLY IN MY CASE!!!!) fibroids (I have some uterine
fibroids), tumours, mineral deposits in joints, etc. etc. This is also called
"protein sparing" because that's what it is. And I have understood that
ketosis is extremely inefficient for producing adequate amounts of ATP,
therefore we don't have as much energy; and that if one taxes the body with
physical (or mental) activity (or "stresses") the body is forced to resort to
glycolysis (extraction of glucose from muscle tissue) again to provide the
necessary energy requirements, thus wasting muscle mass (no longer
"protein-sparing").