The Alkaline Diet (also referred to as the Acid-Ash Diet) is often marketed to the public as a way to reduce the risk of developing cancer and as a treatment for cancer. This idea is based on the premise that cancer thrives in an acidic environment.

The Alkaline diet is being promoted based on the claims that modern-day diets create a more acidic environment in the body.  Promoters of the diet suggest that if we switch to more alkaline foods we can prevent or treat cancer and other chronic diseases such as diabetes and hypertension.

Let’s take a closer look at the claims.

Cancer and pH

Generally speaking, plant-based foods like fruits, vegetables, and seeds are considered to be alkaline, which means they have more minerals that are alkaline in nature such as calcium, magnesium, and potassium.  Meats, dairy, legumes, grains, and nuts are considered acidic as they have higher amounts of amino acids, phosphate, and sulfur which are more acidic compounds.

Some studies conducted in laboratories have shown that cancer cells grow more quickly in an environment that is acidic. For this reason, fans of the alkaline diet believe that avoiding foods that are considered acidic will result in a more alkaline environment in the body, making it is less likely that cancer cells will thrive. However, it’s important to note that large clinical trials testing this claim is lacking and results from cell studies are not sufficient enough to make recommendations from.

It is important to note here that while cancer cells have been shown to grow at a faster rate in an acidic environment it is not an acidic environment that cancer cells have originated from. Cell studies have demonstrated that cancer cells create the acidic environment due to their waste metabolites being more acidic which enables them to proliferate at a faster rate than normal.

The pH Scale

The pH scale ranges from 0 to 14 and is used to identify whether a substance is acidic or alkaline in nature. Acidic substances have a low pH, whereas alkaline substances have a high pH. The neutral pH is  7.

When food is broken down completely in an external environment, think back to general chemistry class and experiments using a bomb calorimeter, the resulting ash can either be acidic or alkaline. As we discussed above, foods that have more amino acids (think meats and beans) and phosphate and sulfur will have more acidic ash when broken down completely.

Conversely, when fruits and vegetables which have higher concentrations of calcium, magnesium, and potassium which are more alkaline are broken down completely the resulting ash will be alkaline. While this is a good experiment to conduct in the laboratory, when food is ingested and broken down in the body, it is never broken all the way down to its resulting ash state.

Therefore, we cannot assume that we are absorbing food in its ash state, and it won’t have the same effect on our body’s pH level as proposed by proponents of this diet.

Your Body’s pH Levels

The pH level of bodily fluid is not equal. The blood’s normal pH is slightly alkaline, ranging between 7.35 and 7.45. This pH is tightly regulated by the body, and any changes outside this pH are treated as a medical emergency.

Stomach acid is very acidic, at pH 3. Stomach acid mixes with all foods consumed, helping to break them down. This mixture then moves along the rest of the digestive system, where it is made more alkaline due to the addition of digestive enzymes. The effect of these enzymes means that the pH of waste products of food is irrelevant, as the digestive enzymes will adjust the overall pH to be alkaline.

Many proponents of the Alkaline diet will recommend a person following this diet to monitor the pH of their urine as an indicator of their overall body’s pH level. This is not a good indicator of the overall pH of the body or general health for several reasons.

1. As stated above, the body releases digestive enzymes to make our digestive juices more alkaline so our bodies can absorb the nutrients into our bodies.
2. As stated above, ANY pH shifts outside of the very narrow pH ranges in our bodily fluids will result in hospitalization and because of that our body will adjust to minor changes in pH in our bodily fluids by releasing more bicarbonate or hydrogen ions to bring the pH back within the normal range.
3. When we measure the pH of our urine we are measuring the amount of WASTE that the body is getting rid of and is NOT a reflection of your bodily pH say in the blood or interstitial fluid or within your cells.

The Bottom Line

Food cannot influence your blood pH.

We know that cancer cells are not restricted to acidic environments and most cancer grows in normal body tissue with a slightly alkaline pH of 7.4. Furthermore, most cancer research is conducted by growing cancer cells in an alkaline environment, not in an acidic environment. And finally, cancer cells grow faster in acidic environments, but cancer creates acidity – it’s not the acidic environment that creates cancer.

The promotion of the alkaline diet and alkaline water for cancer prevention or treatment is not justified. Restricting healthy foods that are considered acidic, such as grains and legumes, lowers the overall nutrient density of your diet and is not recommended.

Our recommendation is to follow a mostly plant-based diet pattern and limit the consumption of red meat, eliminate processed meats and alcohol, and get lots of physical activity for the best protection from cancer.

Kate Ueland, MS, RD specializes in oncology nutrition, primarily working with breast, ovarian, renal, and melanoma cancer patients throughout all stages of the cancer journey at Seattle Cancer Care Alliance (SCCA) in Seattle, WA. As Cook for Your Life’s nutrition advisor and editor, Kate ensures all culinary content adheres to the Academy of Nutrition and Dietetics and follows science-based guidelines.