I don't believe in the acid/base theory. DIfferent parts of the body have different PH levels. And whatever hits the stomach is going to get really acidic really fast, thanx to the hydrochloric acid that gets dumped onto it. Blood levels of acidity are carefully maintained by the body and the number one acidifier of blood is exercise. I have yet to see any scientific evidence that makes me worry about the acid/base concerns that some people are following. In fact, acidity in the gut, caused by cranberry juice, seems to really help some people with urinary tract infections and there is decent research showing that to likely be true. But the acid/base theory would say that acidic food is bad. What I think is that many foods that are 'acidic' also happen to be bad, but for other reasons, like that they are processed and unhealthy foods in general. So of course, you would be healthier if you cut out a bunch of processed foods like soda. HOwever, in order for me to worry about acid/base issues of food, I would first need to see some kind of logic or research that gives credibility to such a theory.
Another interesting link here: http://www.vet.uga.edu/VPP/clerk/morse/index.php I did not see any links on Cordain's site to research proving acid base food intake affects bone health. I have not found any such links as of yet. Studies on various food intakes and various calcium and other nutrient and chemical release into the urine are all over the map as far as results. What you eat changes what you excrete, but looks like they haven't nailed down the mechanisms as to why as of yet. Acid base theory sometimes holds up and sometimes it does not.
What I am seeing from my own research is this: Various types of food DO affect urine PH. Urine PH does NOT affect blood PH. What affects blood PH are things like exercise and illness. Blood PH is controlled by the body via buffering systems like bicarbonate release, kidney function, and breath (CO2) release. Calcium does not seem important for this buffering process. I can't find any scientific mechanism where calcium is part of the normal buffering system. THe buffering system also affects urine PH. Thus, changes in urine PH can be the result of either type of food intake OR buffering processes in the body (and probably other things as well)
But changing urine PH does not act backwards to affect blood PH. So changing your urine PH via different foods will change your urine PH but not your blood PH. The food channels are kept well separate from the rest of the body! (unless you have leaky gut of course) What affects blood PH are things like exercise and illness, not food intake. Of course, if you eat really unhealthy foods and become sick, this could affect buffering ability of the body over the long haul, just because the whole body becomes weak, but it's not necesarily from urine PH levels.
Here is the sticky point that may have added to the confusion. Once your body loses control of acid base balance due to breakdowns in natural buffering systems, THEN this does contribute to calcium loss. THis is mentioned in a small paragraph towards the bottom in the link I provided above. But this calcium loss only occurs if the body is very sick and has already lost control of its buffering systems. It does not happen in a normal individual just because said individual ate a lot of steak that day and not enough veggies.
Thus overacidification of the blood and cells is the result of illness and lack of control over buffering systems. Buffering systems will attempt to respond by breath control and moving the problem out of the body via excretion and acidification of urine. Thus, acidification of urine DUE TO ACTIONS OF THE BUFFERING SYSTEM could signify a problem or it could signify the body's solution to a problem. But acidificaton of the urine due to food intake is probably not a big deal and does not affect blood PH.
Edited to add: In other words, correlation does not imply causation!
The body has strong innate systems to stay in a narrow PH range. Lactic acid is one of them, as is sodium bicarbonate. When lactic acid builds up to much, you breathe heavier to reduce the acidity. The opposite is true, to lower it, try breathing very fast and deeply for a minute or two and then old your breath. You'll be amazed at the amount of time you can hold your breath. Part of this is your body has become too alkaline by breathing too much and needs less oxygen to up the acidity.
So in the end I don't believe for a minute that eating my greens will make any difference in my body's complex PH regulation systems.
In addition to that, we must not forget that some part of our bodies have to be acidic: stomach, sinuses, gut, skin, vagina... The acidity is what kills pathogens. This is why probiotics are lactic-acid forming, they re-establish the correct gut acidity.
I DO believe in the acid/base "theory." We paleos are always reading papers that prove that we are right where diet is concerned, and the CW is wrong. For some reason this acid/base thing is rejected by many paleos despite the evidence. Robb Wolf's site links to this page on Cordain's site, and Wolf recommends everyone start with Cordain's site to find numerous other scientific papers related to the paleodiet.
Having said that, the paleodiet is net base yielding anyways, so it's not like you need to worry about it much.
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