In "Fat of the Land" (aka "Not by Bread Alone"), Stefansson talks of the
effects of eating nothing but pemmican for extended periods of time. He
had experence with this both in the Artic and in experiments with U.S.
military personel before WWII when he tried to get them to accept it as a
survival ration (only the Luftwaffe used it for that purpose during the
war).

For the first few days a person will experence mild diarhea.  Stefansson
attributed this to the intestinal flora in the gut dying due to lack of
vegetable matter.  After this period, defication becomes nearly normal
but occurs only about once a week.

Similar flora die-offs would occur with a water or juice fast.  Just as
the forbidden fruits can cause immune reactions, so can the bacteria and
yeasts associated with their breakdown in the gut.  You can be sure that
the mix of flora in a primate would be of different than that of grass
eater!  Some varients of bacteria found in grass eaters (ie E.Coli)are
well known human pathogens.  The effects of certain yeasts in humans are
very well documented.

For those on a very un-natural diet (ie vegans,macrobiotic et al), the
effects of removing this flora would be magnified.  The pemmican fast
works just as well without the loss of energy.

Ray Audette
Author"NeanderThin:A Caveman's Guide to Nutrition"
http://www.sofdesign.com/neander