Contributor: Melissa Ludick,
The alkaline diet, also known as the acid-base or the alkaline-ash diet, is marketed to the general public as a way to lose weight and to cure diseases such as cancer, diabetes, osteoporosis, and cardiovascular disease.
It is said that if your body is in an “acidic state” it can promote disease. The idea of this alkaline diet is to “neutralize” the body by having alkaline foods and thereby prevent or even cure disease. The Alkaline diet is mostly vegetarian and is not an unhealthy diet if planned properly, but it can become unhealthy if supplements are added to promote “alkalinisation”. Also, because this excludes most animal proteins, you may miss out on valuable nutrients if these proteins are not substituted with appropriate alternatives.
The following table briefly explains the hypothesis and science behind this diet:
| Myths | Facts |
| Cancer thrives in an acidic environment but cannot survive in an alkaline environment. Therefore, eating alkaline foods will prevent or cure cancer. | Tumours do grow faster in acidic environments, but tumours create this acidity themselves. As proven by previous studies, cancer cells also grow in alkaline environments. |
| High protein diets lead to demineralization of bones. It is hypothesised that a diet high in protein may increase acidity through the oxidation of sulphur amino acids and phosphoproteins. Calcium is released from the bones to maintain pH homeostasis in the blood, and eventually causes osteoporosis. | Protein intake has shown to have a protective effect on bone health and strength (1)
There is also evidence that calcium balance is maintained and improved with phosphate intake, which contradicts the acid-ash hypothesis (2) |
| It is hypothesized that a diet high in acidic foods may cause metabolic acidosis and over time result in decreased insulin secretion and consequently diabetes (3,4) | The human body naturally has stringent mechanisms to maintain a pH homeostasis of approximately 7.4. This is known as acid-base homeostasis.. If it were to fall outside of this normal range, it can be fatal and urgent medical help would be needed. |
Dietary intake can affect the pH of your urine, but not your blood.
If you have a meal with a large portion of meat, your urine will most probably test to be acidic several hours later. This is due to your body’s ability to secrete metabolic waste from your system. When protein is digested, the metabolism of the amino acids can produce acids depending on the specific amino acids digested (5). If dietary protein produced acids, pH is rapidly buffered by bicarbonate ions in the blood to produce carbon dioxide that is then exhaled through the lungs, and salts that are then excreted by the kidneys, principally with ammonium (5). During the excretion process of ammonium, filtered bicarbonate is reabsorbed, and the kidneys replace these bicarbonate ions into the blood, creating a sustainable cycle to maintain systemic pH (6).
Take-home message
What you eat can have a profound effect on your health, but there is no clear evidence that the acidity or alkalinity of foods is important when it comes to the treatment or prevention of disease or obesity. Instead, focus on making dietary choices that can truly affect your risk: Eat a wide variety of vegetables, fruits, whole grains and beans; Limit consumption of red and processed meats; Enjoy alcohol in moderation, if at all.
- Calvez J, Poupin N, Chesneau C, Lassale C, Tomé D. Protein intake, calcium balance and health consequences. Eur J Clin Nutr. 2012 Mar;66(3):281-95. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/22127335
- Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA. Meta-analysis of the effect of the acid-ash hypothesis of osteoporosis on calcium balance. J Bone Miner Res. 2009;24(11):1835-40. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/19419322
- Williams RS, Kozan P, Samocha-Bonet D. The role of dietary acid load and mild metabolic acidosis in insulin resistance in humans. Biochimie. 2016 May;124:171-7. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/26363101
- Fagherazzi G, Vilier A, Bonnet F, Lajous M, Balkau B, Boutron-Rualt MC, Clavel-Chapelon F. Dietary acid load and risk of type 2 diabetes: the E3N-EPIC cohort study. Diabetologia. 2014 Feb;57(2):313-20. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/24232975
- Koeppen BM. The kidney and acid-base regulation. Advances in Physiology Education. December 2009;33(4):275-81. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19948674
- Hamm LL, Nakhoul N, Hering-Smith KS. Acid-base homeostasis. Clin J Am Soc Nephrol. 2015 Dec 7;10(12):2232-42. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/26597304/