Richard wrote:
 >The liver is only capable of metabolising a limited amount of >ammonia to
urea. Once this ceiling is reached further protein in >the diet results in a
build up of ammonia in the blood. Ammonia >is toxic, i.e. protein toxicity
a.k.a. "rabbit starvation".

Richard, I'm suspecting this may be another Tall Tale.  however it requires
a good looking at. but do you want to hedge your bets now, or follow the
white line to death or glory?
here's a sample...

And his definition of "rabbit starvation" is a far cry from what Stefansson
described among the Northern Canadian Indians and Inuit back in his book The
Fat of the Land. Cordain, politically correct as ever, claims that the
sickness and wasting that occurs when large amounts of lean animal protein
are eaten occurs because the body has hit a "protein ceiling." REAL rabbit
starvation, however, as defined by Stefansson happened when Inuit and/or
Indians would not get enough animal fat to go along with their catches of
lean meat, which were not preferred by these peoples.
http://www.thincs.org/discuss.cavemen.htm [scroll down to stephen byrnes].

andrew