This ketosis discussion has been very timely for me.  Last Wednesday
evening, I started an experiment.  Here's the theory: It takes about three
days without food for males (2 for females) to induce ketosis.  I'd done
fasting twice, but both times I quit the very minute I reached 72 hours.
The friend who talked me into fasting in the first place would complain that
I was quitting just when I was really starting to see the benefits of
fasting, that hunger was now gone and it wouldn't hurt to go on.  But since
fasting obviously isn't the only way to ketosis, the experiment I came up
with says that I fast for three days, then eat low carb thereafter.  By
doing so, I'd be getting much of the cleansing effects of the fast as well
as a ketogenic kick start.  (Not unlike what mankind would have experienced
in periodic food shortages).

The results so far?  Well, the expected five pound weight loss (again, I'm
not overweight), physical and spiritual renewal from the fast.  Unbelievably
increased senses of smell and taste.  Newfound enjoyment for my food.  And
I'm still in ketosis and losing weight though I started eating the night
before last.

Soon, I'm going to back off the ketosis and start to add some fruit to level
off weight-wise before I get too thin.  But it's been a very interesting
experience.