> The study shows greater protein intake slows down osteoporosis and a
> lower intake the opposite effet, at least in elderly people. -- Marilyn
> 
> http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&li
> st_uids=11127216&dopt=Abstract
> 
> Effect of dietary protein on bone loss in elderly men and women: the
> Framingham Osteoporosis Study. ...

Thanks for that fascinating study, Marilyn. It led me to an excellent
editorial by Robert Heaney that addresses the issue of the acidifying effect
of meats and how it is offset by calcium intake and IGF-1:

Protein intake and bone health: the influence of belief systems on the
conduct of nutritional science
Robert P Heaney
Editorial
http://www.ajcn.org/cgi/reprint/73/1/5.pdf

EXCERPTS and [COMMENTS]:

"A sometimes ignored feature of our study's findings was a positive
correlation between calcium intake and calcium balance, ie, higher calcium
intakes offset the calciuric effects of protein. The mean calcium intake of
the women in our study was 16.5 mmol/d, substantially below intakes now
understood to be necessary for bone health. The aggregate effect of protein
on calcium balance at such intakes does, indeed, tend to be negative
because, at low calcium intakes, the efficiency of intestinal absorption
cannot be increased sufficiently to offset an increase in obligatory calcium
loss. In brief, if protein exerts a negative effect, it is only under
conditions of low calcium intake." 

[This still doesn't explain how the Inuit would avoid calcium loss, given
their low calcium intakes, but my alkaline-organ hypothesis might answer
that.]

"Since our study was reported, an impressive body of literature has proven
that protein tends to have a positive effect on bone overall. ... The most
likely explanation is a protein induced increase in insulin-like growth
factor I (7), which is known to be osteotrophic."

[So IGF-1 can offset the acid-forming effect of meat, and possibly cheese.
This backs what we found during the discussion of betacellulin--that a
certain amount of IGF-1 in the diet from meats is normal and apparently
good, though the levels of IGF-1 in breast milk and bovine milk are
inappropriately high for adults.]

"In parallel with this more or less normal advance of the science, a ferment
in the larger society has arisen out of opposition to the use of animal
products. Although only a tiny proportion of the general public or the
nutritional science community holds this view, the zeal of these groups and
their eagerness to exploit any evidence that suggests harmful effects of
animal products have had a disproportionate effect both on public
consciousness and on the agenda of nutritional science itself."

[He goes on to explain that some studies that associated meat eating with
bone loss or investigated a possible connection were "undoubtedly influenced
by animal-rights activists."]

"[R]ecent sophisticated analyses of the primitive diet, based on
ethnographic studies, analysis of the diets of huntergatherer societies, and
nitrogen isotope ratios of fossil bone collagen, indicate that human
physiology evolved in the context of diets with high amounts of animal
protein (10-12). Although caution has been urged in the interpretation of
such analyses (13), it remains true that there is certainly no evidence that
primitive humans had low intakes of either total protein or animal protein.
That, coupled with the generally very robust skeletons of our hominid
forbears, makes it difficult to sustain a case, either evidential or
deductive, for overall skeletal harm related either to protein intake or to
animal protein. Indeed, the balance of the evidence seems to indicate the
opposite."