PH balance IS confusing. Like, I just had someone tell me that using liquid chlorophyll was bad because the PH was off. Argh!!! That is SO not the point. I mean, would you fail to disinfect a cut in your skin because the disinfectant isn't PH balanced for the skin?!? Argh! LOL!
A diet that is optimized for the body's precious PH balance is talking about BLOOD PH and nothing else. The digestive system is its own amazing environment that makes use of acids and alkalines both. Our blood PH level is of vital importance; if the body cannot maintain a very narrow window of balance, we die in horrible ways. Heart attack, stroke, muscles spasming, mental confusion, all at once.
In order to maintain that balance, the body needs reserves of minerals such as calcium, sodium, potassium, so it can add and subtract molecules as needed. If it doesn't have these from the diet or water, it will do things like rob the bones and teeth of hard bone calcium in order to create blood calcium lactate.
As it maintains the balance, the "used up" or waste acids are excreted in the urine. If the urine is constantly acidic, that tells us that we are not providing enough alkalines or good acids such as fruit acids which are *base once digested* (a base neutralizes acids) to offset the balance. That's where a lot of the misunderstanding about eating a PH diet is, the fact that many acids once digested are the opposite, so people think you shouldn't eat lemon or pineapple, which couldn't be more wrong.
So that, in a nutshell, is blood PH.
When it comes to digestion, food goes from acids in the stomach to alkalines in the small intestine. The food must be reduced to a paste-like material by the teeth and stomach acids so the enzymes can get at the nutrients. Most of absorbtion happens in the small and large intestine, and that requires enzymes. Enzymes are delicate and only work in a more alkaline environment, so the small intestine must flood the digested food mass with base to neutralize the stomach acids so the enzymes can do their good work.
So you want a stomach with plenty of acids or the entire process is compromised. You want plenty of enzymes and reserves of base and alkaline so absorbtion isn't compromised in the small intestine. If either are compromised, then the colon cannot properly do its work to allow absobtion of the base and alkaline minerals still in the food that is turning into fecal matter. So you get a vicious cycle. Depletion because of depletion.