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I want to know if someone is fasting (no food or drink for a whole day) will they have a higher or lower pH than a person who is eating regularly? If so what is an estimate of both of those pH's in the stomach?

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The stomach linings generally secrete gastric acid (HCl, KCl and NaCl) and the native pH of the stomach is around 2. The longer you fast, gastric acid levels keep increasing until it reaches around 1-1.5. The food that you eat increases the pH levels of your stomach because the acid reacts with the food while digestion. Depending upon the type of food you eat, the pH levels of your stomach vary, but it is generally around 4-5 (again it varies depending upon the type and amount of food there is in the stomach).

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  • $\begingroup$ Do you know what goes wrong in heartburn? Clearly eating sometimes generates an excess of H+, which is treated by inhibiting proton pumps. $\endgroup$ – Jory Apr 4 '16 at 5:07
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    $\begingroup$ "The longer you fast, gastric acid levels keep increasing until it reaches around 1-1.5." do you have any references to back this up? I could find ncbi.nlm.nih.gov/pubmed/2395805 and ncbi.nlm.nih.gov/pubmed/2070698 but those don't mention the levels changing when fasting for longer $\endgroup$ – YviDe Apr 4 '16 at 16:04
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    $\begingroup$ @YviDe (ncbi.nlm.nih.gov/pubmed/2395805 ) mentioned the median pH levels come back to nearly 1.7 within 2 hrs after meal. Another interesting article, mentioning stomach pH levels of modern humans to reach 1.5(with some other interesting facts). As I mentioned before, it is not that the pH will keep decreasing with longer fasting period. The initial secretion is high, when food reaches stomach, but based on existing acid levels, the secretion rate stabilizes down. Will post if I find any other relevant article. $\endgroup$ – Grb Apr 4 '16 at 18:53
  • $\begingroup$ @Jory here is an article on what happens in heartburn, but interestingly I found another article which mentions that heartburn is not always a resultant of acid reflux $\endgroup$ – Grb Apr 4 '16 at 18:56
  • $\begingroup$ @Grb okay, I thought with "the longer you fast" , you meant something more like 8 hours and over. The OP is asking about fasting a whole day after all. $\endgroup$ – YviDe Apr 4 '16 at 18:57

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