Can a Low-Acid Diet Help Prevent Cancer?

For years, a pervasive theory has existed that eating a low-acid, high-alkaline diet can help fight and prevent cancer. The premise? Cancer cells thrive in acidity (low pH), but not in alkalinity (high pH), so a diet high in alkaline foods like fruits and vegetables that also limits acidic foods, such as those from animal products, will raise blood pH levels and create an environment in the body that discourages cancer growth.

But is it true?

Not exactly, says Mitchell L. Gaynor, founder of Gaynor Integrative Oncology in New York City, a medical oncologist and author of The Gene Therapy Plan: Taking Control of Your Genetic Destiny with Diet and Lifestyle.

While eating a low-acid diet may help prevent or fight cancer by keeping inflammation within the body at bay, that dynamic has nothing to do with pH levels. “You can’t change your blood pH,” Gaynor says. “Your lungs and kidneys will make sure it stays in the right range, regardless of what you eat.”

Normal blood pH range is between 7.35 and 7.45 for most people, and given the tight regulation of blood pH level by the lungs and kidneys, what you eat — or don’t eat — has little effect on it. PH levels in urine can be affected by dietary factors, but the two systems are completely separate, says Lisa Cimperman, a clinical dietitian at University Hospitals Case Medical Center in Cleveland, Ohio and a spokesperson for the Academy of Nutrition and Dietetics.

As with many dietary theories, this one started from a kernel of truth. Early laboratory experiments suggested that cancer cells would thrive in an acidic environment and research has shown that, due to a tumor’s higher metabolic activity and limitations in blood flow, the microenvironment around them tends to be slightly more acidic, Gaynor says, adding that cancers produce lactic acid through a metabolic process called the Cori cycle.

Because of the way cancer cells metabolize, initially described in the 1950s and termed the “Warburg effect,” these cells have the potential to create an acidic environment where a tumor is located, Cimperman says. But it’s the cancer that creates the acidic environment, not the acidic environment that creates the cancer, she says.

The theory of the low-acid, high-alkaline diet as a cancer preventer or fighter persists because diet is something we can control, Cimperman says. But while the purported link between diet and blood pH is not grounded in sound science, there’s plenty of good that can be drawn from this way of eating when it comes to preventing and fighting cancer.

Whether a food is considered “acidic” or “alkaline” depends on its pH value (measured on a 14-point scale). A pH of seven is considered neutral, with foods below seven considered more acidic and foods above seven considered more alkaline. Alkaline foods such as fresh fruits, vegetables, nuts, legumes and root vegetables are all broken down into short-chain fatty acids that contain prebiotic nutrients that nourish good bacteria in your gut, says Gaynor. These good bacteria help decrease inflammation throughout your body that might otherwise contribute to cancer, while foods such as refined sugar and flour, as well as too much saturated animal fat, create an acidic environment in your gut because they’re difficult to digest, he says.

“All of these ‘high alkaline’ foods are good, not because you’re changing the pH of your blood, but because they’re promoting good bacteria in your gut,” he says.

Despite its advantages, a low-acid diet has not been shown to enhance the body’s response to chemotherapy, even though many claim it can, Gaynor clarifies. Further, he cautions that there’s no need to buy special products that promise to boost alkalinity, such as “alkaline water.”

Cimperman agrees that most individuals can safely follow a high-alkaline diet if they choose to, adding the caveat that some cancer patients already face too many barriers to getting adequate nutrition without further restricting their food intake.

“It’s difficult for some patients to get the nutrition they need to maintain their weight,” she says. “Weight helps many cancer patients better tolerate treatment, so I encourage those undergoing treatment to eat whatever they can tolerate that helps them maintain their weight. There is no ‘perfect’ diet.”