I'm not a doctor, but isn't most food, after it leaves the somach, more or less acidic since the stomach digests food by using hydrochloric acid? Therefore, the question of acid/alkaline "loads" of people's diets is not really relevant since all digested food masses enter the small intestines in a mostly acidic state? At least I would assume it would be acidic after being through the stomach.

I am not seeing the relevance of whether someone eats an acid-based or an alkaline-based range of food...?

As to calcium carbonate taken from bones - isn't it replenished constantly from the foods you eat, vitamin D and minimum load-bearing exercise? In other words if you maintain a healthy lifestyle - there will be no net loss of bone density?  I am not sure if that is the only homeostatic means by which the body addresses the problem of blood acidity, though. 

Some sites that talk about pH:

http://www.usyd.edu.au/su/anaes/lectures/acidbase_mjb/control.html

From http://mcb.berkeley.edu/courses/mcb135e/kidneys.html  4. Regulation of pH. The kidneys prevent blood plasma from becoming too acidic or basic by regulating ions. 

More (from http://www.nurseminerva.co.uk/homeosta.htm#q1):

In what way do plasma proteins act as buffers? Will a deficiency in plasma proteins produce alterations of acid base balance?
2nd December 1998

Recall that a protein is built up from a sequence of amino acids. Some of the amino acids - for example histidine - are able to carry out a buffering function and 'mop up' or release hydrogen ions according to circumstances and help to stabilise pH at an optimal level. (These amino acids have acidic radicals that can dissociate to form weak bases plus hydrogen ions that can function as a buffering system. In case you are not familiar with the term 'buffer', it means a chemical system which helps to maintain the level of acidity/alkalinity of a solution at an acceptable and relatively constant level.)

Proteins are very plentiful inside cells and in various extracellular fluids, and they provide an important and rapid buffering action. In plasma there are three main classes of proteins: albumin, globulin, and fibrinogen, most of which are produced in the liver and lymphoid tissue, and all of which can contribute to the maintenance of acid-base balance. However, they are helped in this vital homeostatic role by other buffering systems:

     bicarbonate and phosphate buffers in the blood and tissue fluid act within seconds or fractions of seconds, like the proteins  
     modulation of the rate of carbon dioxide removal from the blood by the respiratory system helps maintain an appropriate pH, but acts more slowly over minutes rather than seconds 
     excretion of acids and alkalis by the kidneys has a powerful influence on acid-base balance but takes longer - hours and days 

With regard to the effects of a deficiency of plasma proteins - this would depend to some extent on the reason for the deficiency. For example, in nephrosis (a kidney disease) the plasma proteins are lost into the urine, and together with loss of normal kidney buffering functions this would threaten acid-base homeostasis. On the other hand, if the reduction in plasma proteins is the result of under-production of the proteins by the liver, it is possible that the other buffering systems could compensate at least for a time. However, we should also remember the other roles of plasma proteins in producing colloid osmotic pressure, immune reactions, and blood coagulation when considering the effects of a deficiency.

Marilyn


> But the real point is *how* the body balances the net effects of an acidic
> or alkali ash diet.  If the kidneys must resort to using the bones carbonate
> stores to accomplish this neutrality (i.e urine pH no lower than 4, blood pH
> appx neutral), then (as the theory goes) over time bone density is
> compromised.  Research has shown that the SAD provides a net daily acidic
> load (grains, dairy, meat, salt, etc..) while hunter-gatherer diets probably
> provide a net alkaline load.
> 
> I do think there is validity to this argument, but like all things
> associated with diet, it is just one piece of the puzzle.  I'd like to see
> some data on eldery Innuit bone density prior to Westernization; good bone
> health in this population might dispel the acid/base theory or provide
> evidence that the Innuit have genetically adjusted to an all-meat (acid ash)
> diet.
> 
> Best,
> Paul