Potential Renal Acid Load of Foods and its Influence on Urine pH
BibTeX
@article{remer1995potential,
title={Potential renal acid load of foods and its influence on urine pH},
author={Remer, Thomas and Manz, Friedrich},
journal={Journal of the American Dietetic Association},
volume={95},
number={7},
pages={791--797},
year={1995},
publisher={Elsevier}
}
Abstract
The purpose of this study was to calculate the potential renal acid load (PRAL) of selected, frequently consumed foods. A physiologically based calculation model was recently validated to yield an appropriate estimate of renal net acid excretion (NAE); the model depends primarily on nutrient intake data. When nutrient data from actual food composition tables were used, the calculation model yielded PRAL values that ranged from an average maximum of 23.6 mEq/100 g for certain hard cheeses over 0 mEq/100 g for fats and oils to an average minimum of approximately −3 mEq/100 g for fruits and fruit juices and vegetables. By means of these PRAL data (summed according to the amounts of foods and beverages consumed daily and by an estimate of excretion of organic acids [based on body size]), the daily NAE can be calculated. This calculation methodology, primarily based on PRAL, allows an appropriate prediction of the effects of diet on the acidity of urine. For practical applicability in dietetic prevention of recurrent urolithiasis or in other fields of dietetics, the additionally determined correlation (r=.83; P<.001) between NAE and urine pH can be used to ascertain NAE target values for a desired urine pH modification. J Am Diet Assoc. 1995; 95:791-797.
My Summary
Lemons are acidic, but make your urine very slightly more alkaline when you eat them. Why does this happen? Simple: The large amount of citric acid in the lemon doesn’t make it into your urine, but the relatively smaller amount of potassium in the lemon does make it into your urine.
The paper builds a model which predicts the effect of various foods on urine acidity (alkali metals make urine more alkaline, protein-rich foods tend to make urine more acidic), and suggests that this information could be useful in managing kidney stones. Some kinds of kidney stones form more easily in an acidic environment, while others form more easily in an alkaline environment. If you know what kind of kidney stones you are having trouble with, then it might be possible, the paper suggests, to adjust your diet to impede or reverse their growth.
According to a quick skim of wikipedia, this treatment is now standard for uric-acid based stones, but not for other kinds of kidney stones.
Why I read this paper.
One day I went to look up a chart of food acidity, just for fun, and the numbers seemed iffy. Then I noticed that lemons were listed as alkaline. “That can’t be right,” I thought, “lemons are famously acidic. Am I completely misremembering what I learned in school?” So I search “lemons acidity” and find a hoard of nonsense.
Tons of pages online make the claim that lemons are actually alkaline. But lemons are obviously acidic. Some of these people try to resolve the contradiction to basic experience by claiming that ‘oh, lemons are acidic outside the body but become alkaline once inside it. Some go further and say that lemons make your blood more alkaline (no they do not; it’s just the pee). Some go even further and say that “acidifying” food is unhealthy, and that “alkalizing” food like lemons is healthy.
None of these self-proclaimed health experts cite their sources, but these claims were all so obviously bogus that I couldn’t help but dig into them. I’m fairly certain that the “alkaline diet” fad is the result of a long game of telephone starting with this paper linked above.
And just to be clear:
- Are lemons alkaline?
- No, they are more acidic than vinegar. Can eating lemons make my urine more alkaline?
- Yes, technically, barely. But if you need to alkalize your pee, then your doctor will prescribe some antacid tablets. Does having alkaline urine prevent or treat kidney stones?
- It can, depending on the type of kidney stone, but highly alkaline pee can also cause kidney stones. Can eating lemons make my body tissues more alkaline?
- No, just your pee. Your body tissue ph is tightly regulated. Does eating high protein food make my body tissues more acidic?
- No, just your pee. Your body tissue ph is tightly regulated. Is there any way to make my body tissues more alkaline?
- Yes, if you vomit repeatedly. When your body makes stomach acid, it releases bicarbonate into your blood. If it can’t reabsorb the stomach acid, then your blood can become more alkaline. Is it healthier to have more alkaline body tissues?
- No, that’s called alkalosis. It can cause seizures.