Hi Ron;

Maintaining the proper acid level  in the body is one of the functions of 
homeostasis and, as you indicate, removing calcium from the bones is one of 
the means used in order to effect it. That's exactly why it is important to 
eat a nutritious diet - to maintain depleting reserves.

http://www.rcjournal.com/contents/04.01/04.01.0328.asp

[...]

Acid-base homeostasis involves chemical and physiologic processes 
responsible for the maintenance of the acidity of body fluids at levels that 
allow optimal function of the whole individual. The chemical processes 
represent the first line of defense to an acid or alkali load and include 
the extracellular and intracellular buffers, whereas the physiologic 
processes modulate acid-base composition by changes in cellular metabolism 
and by adaptive responses in the excretion of volatile acids by the lungs 
and fixed acids by the kidneys. The need for the existence of multiple 
mechanisms involved in acid-base regulation stems from the critical 
importance of the hydrogen ion (H+) concentration on the operation of many 
cellular enzymes and function of vital organs, most prominently the brain 
and the heart.

[...]

Proponents of the theory that certain foods are necessary in order to help 
you maintain this critical balance are basically spinning a new yarn in 
order to sell their latest book, IMHO.

Marilyn

----- Original Message ----- 

>I read, I think it was in _The Garden of Eating_, that one of the ways the
>body maintains a constant ph is to remove calcium from the bones, using it
>to buffer increasing acidity.