Acid-forming foods make urine more acidic

Do acid-forming foods make urine more acidic?

Pawel Malczewski
facebook twitter google pinterest CONFIRMED
 

Short summary:

Acid-ash  foods contains minerals which lower the pH of fluids. The body has several mechanisms to counteract the action of acid-ash from foods to maintain blood at its optimum acid-base level. One of these mechanisms removes acidic substances through urine via the kidneys and as a consequence urine becomes more acidic. For a quick answer click here.

Explanation

NOTE: Two concepts: acidic food and acid-forming food are often confused. Urine pH is affected by acid-forming food and not by acidic food. (read more..)

The fact that acid-ash foods or acid-forming foods make urine more acidic is well-established by scientific studies. (1)Fenton TR, Lyon AW. Milk and acid-base balance: proposed hypothesis versus scientific evidence. J Am Coll Nutr. 2011 Oct;30(5 Suppl 1):471S-5S. Available here.

Unlike blood pH, the normal values of pH in urine range widely between 4.6pH and 8.0pH. However, it may differ slightly between laboratories. (2)MedlinePlus. Urine pH test. Available here.  Fluctuations of the urine pH within this range indicate that the kidneys do their job making sure that blood pH stays within its narrow range.

How does it work?
After food has been digested and absorbed, the remaining ash makes an impact on the acid-base level within the body. A number of the body’s balancing mechanisms, however, ensure that blood pH remains at the optimal level. One of these mechanisms is via the kidneys which remove through urine the excess of particles (ash) which could disrupt the delicate pH balance in the body.

As a result of the removal of ash through kidneys, urine becomes: (3)Fenton TR, Tough SC, Lyon A, Eliasziw M, Hanley DA. Meta-Analysis of the Effect of the Acid-Ash Hypothesis of Osteoporosis on Calcium Balance. Journal of Bone and Mineral Research. Volume 24, Issue 11, pages 1835–1840, November 2009. Available here. (4)Acidosis. Merc Manual. Available here.

  • less alkaline/more acidic (in other words pH drops) when foods contain more acid-ash or
  • more alkaline/less acidic when foods contain more alkaline ash.

Calculating the amount of acid in urine can be even determined using mathematical formulas (such as Net Renal Acid Excretion NEA and Potential renal acid load PRAL), which use nutrient data from ingested foods. (5)Remer T, Manz F. Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr. 1994 Jun;59(6):1356-61. Available here. (6)Remer T, Manz F. Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc. 1995 Jul;95(7):791-7. Available here.

Conclusion

Back to top
It has been well established that acid-ash absorbed from the diet makes the urine more acidic/less alkaline.

Please note, however, that this scientific fact does not prove that the alkaline diet works which the myth question usually relates to.

References   [ + ]

1. Fenton TR, Lyon AW. Milk and acid-base balance: proposed hypothesis versus scientific evidence. J Am Coll Nutr. 2011 Oct;30(5 Suppl 1):471S-5S. Available here.
2. MedlinePlus. Urine pH test. Available here.
3. Fenton TR, Tough SC, Lyon A, Eliasziw M, Hanley DA. Meta-Analysis of the Effect of the Acid-Ash Hypothesis of Osteoporosis on Calcium Balance. Journal of Bone and Mineral Research. Volume 24, Issue 11, pages 1835–1840, November 2009. Available here.
4. Acidosis. Merc Manual. Available here.
5. Remer T, Manz F. Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr. 1994 Jun;59(6):1356-61. Available here.
6. Remer T, Manz F. Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc. 1995 Jul;95(7):791-7. Available here.

Leave a Reply

Your email address will not be published. Required fields are marked *