Diet doesn't affect blood pH.

Yes, and no! Excerpt that explains it far better than I could: http://drbenkim.com/ph-body-blood-foods-acid-alkaline.htm

When you ingest foods and liquids, the end products of digestion and assimilation of nutrients often results in an acid or alkaline-forming effect - the end products are sometimes called acid ash or alkaline ash.

Also, as your cells produce energy on a continual basis, a number of different acids are formed and released into your body fluids. These acids - generated by your everyday metabolic activities - are unavoidable; as long as your body has to generate energy to survive, it will produce a continuous supply of acids.

So there are two main forces at work on a daily basis that can disrupt the pH of your body fluids - these forces are the acid or alkaline-forming effects of foods and liquids that you ingest, and the acids that you generate through regular metabolic activities. Fortunately, your body has three major mechanisms at work at all times to prevent these forces from shifting the pH of your blood outside of the 7.35 to 7.45 range.

These mechanisms are:

Buffer Systems

Carbonic Acid-Bicarbonate Buffer System
Protein Buffer System
Phosphate Buffer System
Exhalation of Carbon Dioxide

Elimination of Hydrogen Ions via Kidneys

It's not in the scope of this post to discuss the mechanisms listed above in detail. For this article, I only want to point out that these systems are in place to prevent dietary, metabolic, and other factors from pushing the pH of your blood outside of the 7.35 to 7.45 range.

When people encourage you to "alkalize your blood," most of them mean that you should eat plenty of foods that have an alkaline-forming effect on your system. The reason for making this suggestion is that the vast majority of highly processed foods - like white flour products and white sugar - have an acid-forming effect on your system, and if you spend years eating a poor diet that is mainly acid-forming, you will overwork some of the buffering systems mentioned above to a point where you could create undesirable changes in your health.

For example, your phosphate buffer system uses different phosphate ions in your body to neutralize strong acids and bases. About 85% of the phosphate ions that are used in your phosphate buffer system comes from calcium phosphate salts, which are structural components of your bones and teeth. If your body fluids are regularly exposed to large quantities of acid-forming foods and liquids, your body will draw upon its calcium phosphate reserves to supply your phosphate buffer system to neutralize the acid-forming effects of your diet. Over time, this may lead to structural weakness in your bones and teeth.

Drawing on your calcium phosphate reserves at a high rate can also increase the amount of calcium that is eliminated via your genito-urinary system, which is why a predominantly acid-forming diet can increase your risk of developing calcium-rich kidney stones.

This is just one example of how your buffering systems can be overtaxed to a point where you experience negative health consequences. Since your buffering systems have to work all the time anyway to neutralize the acids that are formed from everyday metabolic activities, it's in your best interest to follow a diet that doesn't create unnecessary work for your buffering systems.

For example, your phosphate buffer system uses different phosphate ions in your body to neutralize strong acids and bases. About 85% of the phosphate ions that are used in your phosphate buffer system comes from calcium phosphate salts, which are structural components of your bones and teeth. If your body fluids are regularly exposed to large quantities of acid-forming foods and liquids, your body will draw upon its calcium phosphate reserves to supply your phosphate buffer system to neutralize the acid-forming effects of your diet. Over time, this may lead to structural weakness in your bones and teeth.

This simply isn't true.

Blood pH is regulated without any involvement from the bones. Acids are buffered by bicarbonate ions in the blood, which are replaced by bicarbonate ions that are produced in the kidneys.

As far as the claim that this system can be "overworked," if there is anything to support such a claim, I'd like to hear it.

Blood pH is stabilized by controlling the loss of hydrogen ions & bicarbonate ions in the urine. If you're taking in high acid ( medication, food) and your healthy....the body can recover....however studies have shown that even in healthy individuals who have induced metabolic acidosis--the result is increased output of urinary calcium, which can in turn lead to decreased blood levels, which can have a long term effect on bones/teeth. Here is an abstract if you are interested:
http://www.ncbi.nlm.nih.gov/pubmed/15204429

I get what you are saying--but there is nothing definitive either way in regard to what truly causes metabolic acidosis--the diseases, or is the MA affecting the body toward a diseased state? This in my point.

I have had a conversation similar to this with my MD about adrenal fatigue--which is a very real condition that the medical community doesn't really recognize or treat--because you can't fix it with a pill. And the studies are inconclusive--because there are so many factors that are involved.

The body will compensate when systems are pushed beyond their capacity by robbing other systems. Because it involves so many factors that lead into it, it would be hard to measure. Further--if you bombard the body with processed acidic food it would make sense that over time the compensatory buffer systems in the body would become compromised--especially in people who have a predisposition ( whcih is generally unknow) to such things.