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I was recently having a discussion with someone about whether lemon water actually increases the pH of your body (by which I assume they mean the blood); their claim was that once Citric acid was metabolised it results in an increase in pH due to the "anionic properties of citric acid".

I looked around on the internet at it would seem that this is a common claim circulating around health forums: Example 1, Example 2, etc.

Now to me this sounds like something which cannot possibly be true and appears to be a crazy health fad (they seem to spuriously appear and gain popularity now and again), and I cannot find any scientific papers or articles to support or refute their claim.

Can anyone provide a reliable scientific reference or provide a reasonable scientific explanation (preferably accessible to a layman with only A-level (college level) understanding of chemistry and biochemistry) which either supports or refute the claim that drinking lemon water (citric acid) increases the pH of the blood?

I have crossposted this to Chemistry.SE as well, as it is a crossover between chemistry and biochemistry.

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2 Answers 2

The blood pH is tightly controlled, since variations of it are quite dangerous for us. Under normal circumstances the pH is 7.4 (with a normal range between 7.35 and 7.45). Below that we are talking about acidosis, above it about alkalosis. If the blood pH goes about 7.8 or below 6.8, death will occur. This pH is maintained by the Bicarbonate-buffering system, for details see here and here. Food that we take up does not directly influence the blood pH (and there is also no reason for us to do so, since this is tightly controlled and regulated), so this is a health fad. Details that debunk this myth about it can be found here, here and here.

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The website to which you linked states that Lemons have a "moderate to strong alkaline-forming effect"? How is it that something acidic can form this "alkaline-ash"? –  Shaktal Dec 27 '13 at 13:42
Food gets metabolized in the body and molecules get modified in this process. If you think of the stomach, this is highly acidiy, while the duodenum is pretty alcalic. This gets often mixed up... –  Chris Dec 27 '13 at 13:50

Short Answer:

There was an interesting paper that dealt with the pH of urine when citric acid was consumed.

The summary was: There was no increase in urinary pH or total nitrogen in 24 hours collection of urine.

What This Means:

The food we take does not affect the blood pH directly. Acidic food will cause increased secretion of alkaline components into the digestive tract to neutralize the excess acid. This will cause a fall in the bicarbonate ions concentration (this being the major alkaline buffer) in the blood. This might cause acidosis (depending on how acidic the food is).

The body compensates the decrease in bicarbonate concentration by excreting H+ ions in the urine. Thus urine becomes more acidic when there is a relative state of metabolic acidity in the body. There is also hyperventilation and excretion of more CO2 as this will cause excretion of H+ ions.

HCO3- + H+ ----> H2O + CO2

Incase of alkaline foods, the stomach acid itself would be partly neutralized by the alkali present in food. Thus the body need spend only minimal bicarbonate ions to neutralize the remaining acid.

If there is severe alkalosis body compensates by decreasing the respiratory drive (conserving more H+ ions) and excreting more bicarbonate ions through kidneys.

Compare this with the data obtained from experiment

If consuming citric acid would lower blood pH levels then the urinary pH should increase. As the data shows this is not so, that would mean the citric acid does not contribute to the acidity of food in any significant way even when consumed in large quantities.

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