December 16, 2020 | 6 minute read

When news headlines suggest that following an alkaline diet may help to protect against cancer, we should put them in perspective using one of the hallmark questions of science: is an article showing association or causation? A simple, yet critical, question when you’re deciding whether a certain change in eating habits is really a worthwhile target.

Let’s use that question to review the evidence on whether an alkaline diet can help protect against cancer.

Alkalinity Primer

The body maintains close control on blood pH – how acid or alkaline it is. The lungs, bones and kidneys actively work together in a vital buffering system to keep blood acidity in the safe range.

A diet is not acidic or alkaline based on the pH of the foods themselves. For example, it’s not based on use of foods like lemons and tomatoes that contain more acid. Rather, an acid or alkaline diet refers to the idea that as foods are digested and metabolized, they create a more acidic or alkaline environment in the body. For example, animal protein is a major source of sulphur-containing amino acids that create a higher acid load in the body. Vegetables and fruits are major sources of certain minerals, especially potassium, that may reduce acid load.

An alkaline diet focuses on how greater acid production as food is metabolized requires the body to compensate. It’s not known whether there are long-term effects from body adaptations to maintain blood pH or from small changes within the normal range. Could an acid- or alkaline-promoting diet change the pH of the local environment around and within body cells in ways that change cell health and function?

Questions about Alkalinity and Cancer

In a large population study, scores representing a higher dietary acid load were linked with increased risk of type 2 diabetes. Changing acidity surrounding cells may increase insulin resistance, according to limited laboratory studies. So, some researchers question whether reducing acid load of the diet could improve blood sugar control and reduce risk of type 2 diabetes.

Since elevated insulin levels seem to promote cancer development, this could indicate a connection to cancer risk, too, if this was demonstrated in randomized controlled human studies.

But when it comes to cancer, interest in an alkaline diet mostly stems from laboratory studies suggesting that cancerous tumor cells have an acidic environment surrounding them. Some researchers are investigating whether this acidic environment promotes cancer development or enhances metastasis.

Is an Alkalinity Link Association or Causation?

• Studies of isolated cell cultures and animal studies of cancer don’t necessarily represent what happens within the human body.
• If the area in the body around tumors is more acidic, that doesn’t mean that an acidic body environment caused the cancer. Rather, it could be a result of cancer cells’ high metabolic rate that generates acids (like lactic acid).

Alkaline Diet: The Right Focus?

A systematic review on alkaline diets and cancer found little published or unpublished research. None supported the idea that increases in acid due to dietary choices causes or contributes to cancer development.

Since that review, an observational study found that diets categorized as more acid-producing were associated with increased risk, and alkaline diets were associated with decreased risk, of estrogen receptor-negative (ER-) and triple-negative breast cancers.

Another observational study found that scores suggesting a more acidic diet were linked with increased markers of inflammation and poorer outcomes among some early-stage breast cancer survivors.

Are Findings From Alkaline Diets Association or Causation?

• Diet scores associated with blood and urine pH are derived from calculations based on total animal protein consumption and levels of one or a few minerals.
• Limited human studies demonstrate that a diet score based on components that seem responsible for its acid- or alkaline-promoting tendencies is linked with markers of pH in the blood and urine. However, it’s not clear whether the small changes in blood pH from modest differences in diet have a biological effect on health.
• Research shows that the local environment around cells (the “microenvironment”) may be important in cancer development. But evidence so far points more strongly to changes in metabolic factors like insulin and leptin (a hormone closely related to body fat levels) promoting cancer cell growth and reproduction, according to Neil Iyengar, MD, a medical oncologist and cancer researcher at Memorial Sloan Kettering Cancer Center. Excess body fat can also promote cancer development through increases in inflammation surrounding cells and throughout the body. “There is no convincing evidence that breast cancer survivors are at increased risk for metabolic acidosis or other acid-base disorders,” says Iyengar, who specializes in breast cancer care.
• A diet that limits animal protein and includes an abundance of vegetables and fruits would score as an alkaline diet, but could be affecting health through antioxidant nutrients and phytochemicals, fiber content and support for a healthy gut microbiome, and help maintaining a healthy weight.

How an Alkaline Diet Compares with Cancer Prevention Recommendations

The alkaline diet generally encourages higher consumption of vegetables and fruits and limits meat intake. That’s consistent with AICR’s evidence-based recommendations for a diet to reduce cancer risk. The diet also calls for avoiding added sugars. Recommendations for cancer prevention and overall health also advise limiting added sugars – not because of effects on acid production, but because too much can make it harder to avoid weight gain that can lead to inflammation and elevated levels of hormones like insulin.

But there can be important inconsistencies between an alkaline diet and cancer prevention recommendations. Some advice for this diet includes limiting all grains (even whole grains), coffee, fish, dairy products and oils generally considered healthful (like olive and avocado oils). Some encourage selective choices among fruits, vegetables, legumes and nuts, but limiting others. Moreover, the focus on changing your body’s pH to protect against cancer can make supplements or alkaline mineral waters seem like an easy solution, even though there’s no evidence of cancer protection.

Are Alkaline Diets Associated with Cancer Prevention Recommendations?

• If your interpretation of an alkaline diet limits whole grains and beans, that doesn’t fit the plant-focused eating pattern recommended to reduce cancer risk.
• Although evidence on other foods that some advocate limiting for an alkaline diet (coffee, fish, healthy oils) are not necessary to meet AICR recommendations, avoiding them as a potential influence on body pH can needlessly remove a food you enjoy and make a healthy diet more complicated.
• “We do not yet have data regarding how specific dietary factors may impact the tumor microenvironment,” says Iyengar. Still to come, “We do have an ongoing study which will assess the impact of a whole food plant-based diet on the breast microenvironment.”

Summary

A diet higher in fruits and vegetables – which is what some people mean when referring to an alkaline diet – supports a host of health benefits. But until we have more human evidence on whether a diet’s acid load influences cancer development or outcome, stick with only the elements of an alkaline diet that are consistent with the bigger picture of diet and cancer research. Use the AICR recommendations as a guide to an overall healthful eating pattern with a wide range of protective nutrients and compounds.