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Dozens of sites throughout the internet nowadays, seemingly concerning nutrition, essentially try to convey the same message: alkaline food helps to regulate your internal pH.

Having read some simple notion on the subject, I learned body fluids' pH has to be maintained always in a quite strict range (between 7.35 and 7.45), although in the stomach it goes under 3 because of gastric juices.

Hence, is there any scientific evidence backing the aforementioned statement?

  • no, no, and hell no. Internal pH regulation is achieved via several buffer mechanisms that are of life-and-death importance and cannot and are not left to the whims of whatever food our ancestors could find or not find at any given moment. We also don't directly absorb precisely what we eat, things get preprocessed, so the equation is not as simple as eat A, absorb A. – mismas Nov 6 '16 at 19:29
  • @mismas: Since food is part of this buffer mechanism, "no, no, and hell no" could be a but misleading, but I assume you just wanted to emphasize that it is a bit more complex ;). – bluenote10 Oct 7 '17 at 14:20
  • Actually, the buffer mechanisms are the carbonic acid/bicarb system (by far the most influential), the phospate buffer, and the protein buffer (the protein being mainly haemoglobin). Alkaline veggies are not directly involved. – mismas Oct 7 '17 at 18:53
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Yes, there is evidence that alkaline food affects internal pH, but it is important to note that the regulation of internal pH (acid-base homeostatis) has other contributing factors, which is why the impact of food is subtle.

I'm mainly aware of evidence from studies on sodium bicarbonate, as an example for a simple way to supplement alkaline food.

So technically you could say that alkaline food "helps to regulate internal pH", but it is a very weak influence. To emphasize the impact of other contributing factors to blood pH, it is also interesting to look at something like this:

  • M. Kox et al: Voluntary Activation of The Sympathetic Nervous System and Attenuation of the Innate Immune Response In Humans

    This article studies the effect of the Wim Hof method, in particular its breathing technique. The breathing technique basically alternates between voluntary hyperventilation and breath holds. The supplementary material features a video of one subject performing the breathing technique, including monitoring of blood pH over the course of the exercise. The subject has a basline blood pH of 7.4. During hyperventilation, blood pH increases over 7.6 as a result of the reduced carbon dioxide levels in the blood. During breath retention, carbon dioxide levels normalize and the blood pH falls (almost) back to the baseline level. Note that these effects on pH are very quick compared to nutritional influences.

This example shows why it is difficult to separate the effect from alkaline food from other factors contributing to pH homeostasis. Taking a few deep breaths or holding your breath has a very immediate effect on blood pH, which can easily bias the more subtle effect from an alkaline diet. I'm not an expert, but I could imagine that the respiratory rate is even determined by dietary factors. Thus, instead of studying the effect on internal pH, it might be more sensible to show that an alkaline diet leads to reduced breathing in the long term, because the body could maintain the same pH level even with higher carbon dioxide levels.

  • @LangLangC: Maybe I should have put it as the simplest way to supplement alkaline food? Dissolving NaHCO3 in water has a pH of ~9 depending on the concentration/water. I assume researchers prefer sodium bicarbonate over more complex alkaline foods because the supplementation is more straightforward and controllable. – bluenote10 Oct 7 '17 at 15:32
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As for the studies... I would think the first study actually proves my point. People were given 20+g of bicarb and then exercised nearly to death (as evidenced by their ICU worthy ABGs), and yet they survived. Furthermore, they survived with the buffers on the sigmoid curve, which means these extreme values in ABGs represent a very very extreme assault on the body. With a minor glitch that a change to a more alkaline diet is... no... this sort of system will not register a change, simply because it is built to withstand the extremes of external environment with minimal changes to the internal environment. If the ancestor in my first comment could have their blood pH affected by something as minor as a change in alkalinity of an otherwise non-toxic diet, they would have no chance of withstanding a sustained extreme physical effort that is hunting an animal without firearms or running from an animal hunting them.

  • This is a probably excellent comment, alas, posted as an answer, lacking references. This violates policy. If you want to answer the question, please do so, looks as if you have all the knowledge and tools to do it. I am looking forward to it. – LаngLаngС Oct 7 '17 at 20:32
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    Could you please clarify your first point? The blood pH was elevated even before the exercise, i.e., just 90 minutes after supplementing with bicarb. It is not clear to me why the intensity of the exercise matters. On your second point: Note that downing 500 ml of a pH ~9 food already is an extreme case (trying to go more alkaline will just give you the runs, I remember seeing studies specifically on this) and yet the blood pH only reacts by a tiny 0.05. So I agree that the system "withstands the extremes of external environment", but there is clear evidence that it is not entirely unaffected. – bluenote10 Oct 7 '17 at 20:52
  • Intensity of exercise matters very much, because it causes lactacidosis, it´s why people thought adding alkaline foods would help in the first place. And yes, the pH was elevated immediately after bicarb, but you´ll notice it stayed within the normal range. Why? Because the body wants it there and is working very hard to maintain it there. And yet... exercise sent both groups deep into acidosis, in spite of extreme alkaline administration. Lesson? You can´t really supplement your way into pH regulation, the system is just not sensitive enough to what you can reasonably ingest. – mismas Nov 25 '17 at 11:57
  • As for clear evidence that the system is not unaffected... actually no. For one thing, these graphs lack assessment of statistical significance. And even if you proved statistical significance, it still doesn´t prove real life relevance. And even if we agreed that there is a relevant difference in pH of 7.39 and 7.42, there´s still the fact that these measurements were taken after 90 minutes. What about after 6 or 12 hours, which is a much more relevant time frame for elimination of bicarb? – mismas Nov 25 '17 at 12:02
  • Back to the original question: no, there is no need to regulate systemic pH with food. It´s already regulated, and if not, you´re among the most critically ill people, and supplements won´t save you, nor are you able to consider them. Furthermore, your body is made so that even extreme ingestion of alkaline food (as above) will have only a transient negligible effect on your systemic pH, because to have it any other way could be deadly whenever you strayed from your diet. And if extreme supplementation only causes a transient glitch in pH, how would one actually regulate it with supplements? – mismas Nov 25 '17 at 12:13

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