I think Loren Cordain may be drawing on some work by Speth and Spellman,
which I can't find at the moment.  But basically they do mention the lack of
fat being a problem and also IIRC a protein ceiling of around 300 gms a day.
Unfortunately they don't explain the "why" of it very well

Sean McBride
University of Queensland
Brisbane, Australia
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