An idea that has generated much interest within the complementary medicine and holistic nutrition fields is that of the acid-base (or acid-alkaline) balance of the foods that we eat and the potential harm that a diet that is too 'acidic' can cause.
The various compounds that result from the digestion of food and end up circulating through our bodies for eventual utilisation and/or excretion will be either acidic or alkaline.
It is not technically correct to say that the blood ‘will become overly acidic’ as many claim, because blood pH, and cellular pH is one of the most tightly controlled mechanisms in the body, however there may be significant general health effects from having a diet that is too acidic and many of these stem from our need to ‘buffer’ blood and cells that are potentially too acidic (bring them back to a normal pH range.)
Animal proteins and cereal grains contain sulphur containing amino acids methionine, cysteine and homocysteine which when oxidised form sulphate, a major contributor to blood acidity (1) and in these foods sulphate is balanced with acid forming types of potassium, unlike potassium compounds in fruits and vegetables which are considered to be alkaline forming.
Dairy products and milk especially are often considered to be acid forming and some authors maintain that they may be damaging to bone health in comparison to the mainstream assumption that dairy intake improves bone density due to increased calcium intake. A 2011 review in the American Journal of Clinical Nutrition refutes these claims however, and offers the following conclusions:
- Measurement of an acidic pH urine does not reflect metabolic acidosis or an adverse health condition.
- The modern diet, and dairy product consumption, does not make the body acidic.
- Alkaline diets alter urine pH but do not change systemic pH.
- Net acid excretion is not an important influence of calcium metabolism.
- Milk is not acid producing.
- Dietary phosphate does not have a negative impact on calcium metabolism, which is contrary to the acid-ash hypothesis.
- So it is considered that an increased urinary acid load as a result of a high acid diet does not increase systemic acid, although this may not be purely due to the kidneys excreting the increased acid and may also result from increased internal buffering.
How We Regulate Blood pH
Our acid-base balance is finely regulated in the first instance via changes in respiratory rate and volume, where an increased excretion of carbon dioxide (CO2) serves to reduce net acidity (2).
The kidneys are our major system for ‘buffering’ the blood and reducing net acidity. However kidney function declines as we age and net acidity is considered to also rise over our lifespan.
Many experts maintain that the ‘buffering’ capacity of the respiratory system and the kidneys is more than adequate to cater to changes in dietary acid intake, others however point to other ‘secondary buffers’ including the breaking down bone of tissue to supply calcium (a highly basic compound) and the break down of muscle to free up glutamine (a highly basic amino acid and the most abundant amino in muscle tissue). These factors may result in lower levels of muscle mass, impaired recovery and reduced glutamine stores that may also play a role in reducing immunity and impairing gut health.
When blood pH is elevated, even fractionally, there may be additional effects of greater inflammation and increased insulin resistance, both of which are co-factors in the development of heart disease, diabetes, cancer and other metabolic disorders.
Benefits of an Alkaline Diet
Increased intake of fruits and vegetables in an alkaline diet may benefit bone health, reduce muscle wasting, as well as mitigate other chronic diseases such as hypertension and strokes. Increases in growth hormone with an alkaline diet may improve many outcomes from cardiovascular health to memory and cognition. Increased intracellular magnesium, which is required for the function of many enzyme systems, is another added benefit of the alkaline diet, and increased alkalinity may result in added benefit for some chemotherapeutic agents that require a higher pH.
Surprisingly at the present time there doesn’t seem to be enough evidence to recommend an alkaline diet for improving bone health (3) and outcomes of alkaline diet studies do not seem to suggest an improvement in bone health or reductions in osteoporosis (4), however there are some tangible benefits suggested as a result of alkaline diets.
Who Does an Alkaline Diet Benefit?
Weight-loss and metabolic disorders
An alkaline diet may lower cortisol levels and reduce insulin resistance (5) a major causative factor in obesity, and reduce hypertension (high blood pressure) and other cardiac risk factors (6).
An alkaline diet may also be effective for removing excess uric acid from the body (7) thereby reducing symptoms for gout sufferers.
Muscle gain and performance
Small increases in muscle mass have also been observed in women following an alkaline diet (8) and an alkaline diet rich in fruit and vegetables increases lean body mass in older adults (9). Reduced muscle performances has been demonstrated with chronic ingestion of a highly acid forming diet (10).
A more acidic diet is also considered formative for kidney stones, with lower acid diets and higher vegetable intake recommended for those at risk of kidney stones (11).
1. The Alkaline Diet: Is There Evidence That an Alkaline pH Diet Benefits Health? (2012). Journal of Environmental and Public Health, 2012. doi: 10.1155/2012/727630
2. Davenport, H. W. (1974). The ABC of acid-base chemistry: the elements of physiological blood-gas chemistry for medical students and physicians: University of Chicago Press.
3. Wynn, E., Lanham-New, S. A., Krieg, M.-A., Whittamore, D. R., & Burckhardt, P. (2008). Low Estimates of Dietary Acid Load Are Positively Associated with Bone Ultrasound in Women Older Than 75 Years of Age with a Lifetime Fracture. The Journal of Nutrition, 138(7), 1349-1354.
4. Hanley, D. A., & Whiting, S. J. (2013). Does a High Dietary Acid Content Cause Bone Loss, and Can Bone Loss Be Prevented With an Alkaline Diet? Journal of Clinical Densitometry, 16(4), 420-425. doi: http://dx.doi.org/10.1016/j.jocd.2013.08.014
5. McCarty, M. F. (2005). Acid–base balance may influence risk for insulin resistance syndrome by modulating cortisol output. Medical Hypotheses, 64(2), 380-384. doi: http://dx.doi.org/10.1016/j.mehy.2004.01.045
6. Adeva, M. M., & Souto, G. (2011). Diet-induced metabolic acidosis. Clinical Nutrition, 30(4), 416-421. doi: http://dx.doi.org/10.1016/j.clnu.2011.03.008
7. Kanbara, A., & Seyama, I. (2011). Effect of Urine pH on Uric Acid Excretion by Manipulating Food Materials. Nucleosides, Nucleotides and Nucleic Acids, 30(12), 1066-1071. doi: 10.1080/15257770.2011.596498
8. Welch, A. A., MacGregor, A. J., Skinner, J., Spector, T. D., Moayyeri, A., & Cassidy, A. (2013). A higher alkaline dietary load is associated with greater indexes of skeletal muscle mass in women. Osteoporosis International, 24(6), 1899-1908. doi: 10.1007/s00198-012-2203-7
9. Dawson-Hughes, B., Harris, S. S., & Ceglia, L. (2008). Alkaline diets favor lean tissue mass in older adults. The American journal of clinical nutrition, 87(3), 662-665.
10. Mithal, A., Bonjour, J. P., Boonen, S., Burckhardt, P., Degens, H., Hajj Fuleihan, G., . . . Dawson-Hughes, B. (2013). Impact of nutrition on muscle mass, strength, and performance in older adults. Osteoporosis International, 24(5), 1555-1566. doi: 10.1007/s00198-012-2236-y
11. Trinchieri, A., Maletta, A., Lizzano, R., & Marchesotti, F. (2013). Potential renal acid load and the risk of renal stone formation in a case-control study. European journal of clinical nutrition, 67(10), 1077-1080.