The Truth About Alkaline Diets

Here's what you need to know...

Alkaline diets are becoming a trend. Diets lower in acidic food and higher in basic (alkaline) food are gaining popularity.
The Western diet is highly acidic. Meat, dairy, and grains are generally acidic while foods such as fruits and vegetables are generally basic.
Regardless of diet, your body will maintain pH. Blood pH is kept within a narrow window in those who are healthy.
Any variation of pH caused by food is rapidly regulated. There's no evidence that a healthy individual can negatively alter blood pH through diet.
Acidic diets may cause tooth decay. But these diets have not been linked to muscle loss, bone loss, cancer, poorer skin health, greater susceptibility to infection, or reduced energy levels.

Alkaline diets are growing in popularity. Those who use them believe that the problem with the average Western diet is its acidity – having a pH lower than 7.0. They say a number of health problems are caused by this acidity and that it can even cause muscle loss. Is this true?

Here are the facts. Eating alkaline foods – foods with a pH greater than 7.0 – banishing acidic foods, and taking alkaline products won't do much to "restore the body's pH" and prevent these health conditions. These claims just aren't supported by science. Let's break it down.

Which Foods are Acidic or Basic?

Meat, dairy, and grains are generally acidic while foods such as fruits and vegetables are generally basic/alkaline.

Alkaline diets are high in fruit and vegetable consumption and limited in meat, dairy, and grains. Sugar is generally thought to be acidic and is restricted in alkaline diets, but sugar is actually neutral. Many individuals following alkaline diets consume lemon juice or apple cider vinegar because they are touted as basic, but these are also acidic. Vinegar is acetic acid and lemon juice contains citric acid.

Can Diet Alter Blood pH?

Any slight variation of pH caused by dietary intake is rapidly regulated by the kidneys. Therefore, dietary acid intake cannot alter blood pH.

The kidneys play a key role in maintaining pH balance throughout the body. Normal physiological pH of blood is tightly controlled between 7.35 and 7.45. When blood becomes acidic, the kidney excretes H+ and produces bicarbonate ions which enter the blood and neutralize blood pH to keep it in this narrow range. As a result of the kidney's role in acid-base balance, urine pH can range from 4.5 to 8.2 and can be influenced by dietary intake. However, urinary pH is not a good measure of blood pH, which is maintained within a narrow range in individuals with normal kidney function.

Did We Evolve to Eat Low-Acid Diets?

Although blood pH is not altered by the diet in healthy individuals, advocates of the alkaline diet claim that humans evolved to eat low-acid diets. This is not true.

A recent study on the dietary patterns of pre-agricultural humans found that roughly half consumed an acidic diet. As a side note, I would also advise against making any dietary recommendations (for performance, health, or otherwise) off of the diets of pre-agricultural man, a population whose average life span was a fraction of ours today and who commonly died of starvation.

What is the Role of pH in Digestion?

The acidic environment of the stomach and neutral-to-basic environment in the small intestine occur regardless of what food is consumed in the diet.

When food is swallowed, it enters the stomach where hydrochloric acid creates a pH range of 1.5 to 3.5. This acidic environment serves several purposes including: denaturing of proteins, activation of pepsin (an enzyme that breaks down protein), and protection from bacterial infection. Once food exits the stomach, it enters the small intestine where bicarbonate is released to neutralize the acidic pH. This allows enzymes in the small intestine to work at their optimal rate to digest proteins, carbohydrates, and lipids.

What Does Alter Blood pH?

Due to the kidney's key role in regulation of blood pH, people with impaired kidney function are often susceptible to fluctuations in blood pH levels. Conditions such as diabetic ketoacidosis, alcohol toxicity, respiratory disorders such as emphysema, carbon monoxide poisoning, and others can alter blood pH. Remember, in healthy individuals blood pH is maintained between 7.35 and 7.45.

Consumption of large amounts of bicarbonate can alter stomach pH. However, this also results in GI symptoms/distress and may alter normal digestion of protein in the stomach since the low pH is an integral part of this process. Bicarbonate supplementation has been shown to increase blood pH by as much as 0.08 but this is a short-term increase that's quickly regulated.

3 Myths of Alkaline Diets

Alkaline diets prevent muscle loss. Dietary acidity does not influence risk rate of muscle loss in healthy individuals. Proponents of alkaline diets, particularly in the fitness world, often list prevention of muscle loss as a major benefit of following an alkaline diet. This stems data in patients with chronic kidney disease who experience muscle wasting for a number of reasons including metabolic acidosis. In healthy individuals, blood pH isn't impacted by diet. Therefore, dietary acidity has no effect on rate of muscle loss. Furthermore, acidic foods such as meat and dairy are complete proteins that support muscle repair and help prevent muscle loss.
Alkaline diets prevent bone loss. Dietary acidity does not cause bone loss in healthy individuals. A recent review on this topic concluded there was no evidence of an effect of dietary acidity on calcium balance, bone metabolism, or osteoporosis risk. And to top it off, a higher protein intake (primarily coming from acidic foods) has been associated with a reduced bone loss.
Alkaline diets prevent cancer. The concern about dietary acidity and cancer stems from the fact that cancer cells in the body grow in an acidic environment. However, this acidic environment is the result of cancer cell metabolism. The cancer cell is causing the acidic environment helping it to grow rather than the body being acid and causing cancer cells to grow. In addition, a recent study has shown that cancer cells can also grow in an alkaline environment. And there's no mechanistic evidence that dietary acid consumption results in increase cancer risk.

Other Health Claims

Dietary acid may have a detrimental impact on oral health. Foods with pH less than 5.5 can damage tooth enamel. Therefore, excessive amounts of highly acidic foods or beverages (soda) should be avoided.

That aside, proponents of alkaline diets often cite a number of other health benefits including: better skin health, resistance to infection, and more energy. However, there's no scientific evidence to support any of these claims. As a whole, alkaline diets do not live up to the hype. Blood pH can't be altered through dietary acid intake in healthy individuals. As a result, health claims made by those who follow an alkaline diet are not supported by the scientific literature.

However, one thing we can take from the dietary practices of those who follow alkaline diets is a recommendation for a diet high in a variety of fruits in vegetables. These foods are beneficial for their nutrient content, not because they are alkaline foods. For individuals with normal kidney function, there's no need to worry about the pH of foods you're eating.

References

Remer, T. and F. Manz, Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc, 1995. 95(7): p. 791-7.
Stipanuk, M.H. and A.C. Marie, Biochemical, Physiological, and Molecular Aspects of Human Nutrition. 3 ed2012: Saunders.
Carr, A.J., et al., Effect of sodium bicarbonate on [HCO3-], pH, and gastrointestinal symptoms. Int J Sport Nutr Exerc Metab, 2011. 21(3): p. 189-94.
Koeppen, B.M., The kidney and acid-base regulation. Adv Physiol Educ, 2009. 33(4): p. 275-81.
Bonjour, J.P., Nutritional disturbance in acid-base balance and osteoporosis: a hypothesis that disregards the essential homeostatic role of the kidney. Br J Nutr, 2013. 110(7): p. 1168-77.
Strohle, A., A. Hahn, and A. Sebastian, Estimation of the diet-dependent net acid load in 229 worldwide historically studied hunter-gatherer societies. Am J Clin Nutr, 2010. 91(2): p. 406-12.
Mitch, W.E. and J. Du, Cellular mechanisms causing loss of muscle mass in kidney disease. Semin Nephrol, 2004. 24(5): p. 484-7.
Tucker, K.L., M.T. Hannan, and D.P. Kiel, The acid-base hypothesis: diet and bone in the Framingham Osteoporosis Study. Eur J Nutr, 2001. 40(5): p. 231-7.
Martinez-Zaguilan, R., et al., Acidic pH enhances the invasive behavior of human melanoma cells. Clin Exp Metastasis, 1996. 14(2): p. 176-86.
Robey, I.F., Examining the relationship between diet-induced acidosis and cancer. Nutr Metab (Lond), 2012. 9(1): p. 72.
Moynihan, P. and P.E. Petersen, Diet, nutrition and the prevention of dental diseases. Public Health Nutr, 2004. 7(1A): p. 201-26.