Hi Ken, 
I've been giving some thought to your posts and thought I'd jot down some of
my ideas on this issue.  

I'm not sure where Cordain got his information about meats altering ph to
the point where excessive calcium had to be scavenged to buffer the highly
acidic process of meat digestion. It may be that, because he advocates lean
meat, he was looking at it from the perspective of lean meat digestion. If
that's the case, then it probably applies to those who are eating a diet
that contains 30% fats, which is what he recommends.  

Here is what I've been thinking: Fats are not well digested in the stomach
or earlier in the digestive process, partly because the mouth and esophagus
are weakly acidic and most digestive enzymes (other than amylase) don't work
very well  in acidic environments. The stomach is highly acidic so not much
breakdown of fats occurs there either. It is not until the fats reach the
duodenum, and the buffering secretions of bile and bicarbonate raise the ph
of the duodenum that lipase can begin to do its work of digesting fats. ( I
won't go into the emulsification and absorption process as that is not
currently relevant.)

Calcium salts certainly form a small but significant part of this bile, and
hence, are active in the buffering process. However, more than 96% of these
salts are reabsorbed in the large intestine. Thus, diets high in fats should
not result in significant calcium losses as calcium is abundantly available
in many of our foods and most foods would contain enough calcium to
replenish the ~ 4% losses from bile salts. 

I could see, in the context of a low fat diet, how homeostatic devices might
be required to buffer the highly acidic chyme, as it enters the duodenum, by
moving calcium from the bones into the duodenum (although I'm not at all
familiar with this process and have never heard of it before). However,
normal digestion of larger proportions of fat, with adequate bile production
and secretion, should do the job without excessive calcium loss. 

It may be useful to look at a situation where we know that fat digestion is
compromised. In the context of celiac disease, it has long been understood
that CCK production is often compromised or abolished. This messenger is
produced in the intestinal mucosa, in response to fats arriving in the
duodenum, and signals the gall bladder (where bile secretions are stored
between meals) to contract and push bile down a duct to the duodenum. When
CCK production is halted or compromised (as in the case of many celiac
patients) the absence of bile doubtless causes many digestive problems,
including poor fat absorption due. Similarly, it would be necessary to
buffer the acidic chyme moving from the stomach to the duodenum, which might
result in significant calcium losses. 

It is well established that people with celiac disease are more inclined to
osteoporosis than the general population. It was long assumed that this
inclination was due to calcium malabsorption. However, Marsh et. al.reported
in 1994 that "overall negative calcium balance in gluten sensitivity is the
result of high rares of endogenously secreted calcium, rather than to acutal
failure of calcium absorption" (American Journal of Gastroenterology vol 89;
no 12).  If this applies to a lean meat diet (and I suspect it does) then
Cordain has provided a clue to the flaw in his recommendation for less than
30% fat in the diet. 

I don't know if my thoughts offer you a more palatable perspective. I don't
even know if I could fully defend my thinking at this point. However, I do
know that something is causing the current epidemic of osteoporosis and it
does seem to be rising in parallel with low fat recommendations. It was your
repeated posts and the comment on Tim Ferriss' blog about Mary Enig that
first got me thinking about this issue from a new perspective. 

Here is the comment abou Mary Enig: 
"You can't turn on the television without being told you need calcium for
your bones, but do you recall ever hearing that saturated fat is required
for calcium to be effectively incorporated into bone? According to one of
the foremost research experts in dietary fats and human health, Mary Enig,
Ph.D., there's a case to be made for having as much as 50 percent of the
fats in your diet as saturated fats for this reason." From:
http://www.fourhourworkweek.com/blog/2009/09/06/saturated-fat/

      
Best Wishes, 
Ron