I was asked recently if it’s important to prevent the body from being “too acidic,” for someone who has cancer. This topic has come up again and again over the nearly two decades during which I’ve worked in the cancer nutrition field. Given how common this belief is, it’s certainly worth discussing.

Possible origin of the belief that an “acidic body” causes cancer

There is a significant contingent of the complementary, alternative, and integrative medicine communities that believes keeping the body “alkaline,” or less acidic, is one of the key factors for optimal disease prevention. There also is a belief that an “acidic environment favors cancer.” This belief likely arose from the fact that cancer cells, with their unusual, extremely rapid metabolic activities, tend to make the micro-environment in and around, a tumor more acidic. However, this acidic tumor micro-environment does not appear to measurably shift total body pH to be more acidic.

Further, there is no evidence that making the body itself more alkaline will have any affect on the acidity of the tumor. So, the observation that tumors are acidic may have led some people to conclude (mistakenly) that acidic environments cause tumors. In reality, it is tumors that cause acidic environments. Thus far, research simply does not support that a large focus on shifting total body pH to be more alkaline will improve cancer outcomes. Perhaps future studies will show some benefit of “being more alkaline”, but for now, that research does not exist.

Of interest, cancer researchers are investigating ways to alter the pH of cancer treatment medications, so they can better penetrate into tumors. This is an exciting line of study, but it doesn’t point to any benefit of trying to “de-acidify” the body overall as part of cancer treatment.

One exception

As an aside, it’s important to note that in later stages of cancer, when a person has significant metastatic disease – tumors that have spread throughout the body – the body can become acidic. However, this is not related to the tumor acidity itself. In advanced cancer, a condition called cachexia can occur.

Cachexia causes the body to inappropriately use lean tissue, such as muscle, for energy, and to fail to use fat and carbohydrates – the more appropriate sources of fuel (calories). This causes wasting and weakness, and can increase body acidity. However, this cannot be reversed with diet alone, and making the body more alkaline will not stop cancer cachexia from occurring in advanced cancer cases.

Even if you believe it, how do you measure it?

The other problem we face is how to measure acidity. Urine acidity, which is a test that many alternative medicine practitioners use to convince people to take “alkalinizing supplements,” is very “short term” and reactive. A change in what you put in your mouth can immediately, and drastically alter urine pH within hours. But we don’t know if this means that what you put in your mouth has done much to your blood and body’s pH levels over the long term. One short-term study (one week) demonstrated urine and blood pH could be increased with an alkaline mineral supplement, but even these study authors concluded that they had no idea if this had any implications for long-term health.

In the end, most agree that diet can nudge blood and body pH, but for how long, and to what effect, isn’t clear in the majority of cases.

It is important to note though, that while body acidity can be altered by general diet patterns (more on that below), these changes are very small. A pH of 7 is neutral. Above pH 7 is alkaline, and below 7 is acidic. Blood pH is naturally, slightly alkaline. Healthy blood pH levels range from approximately 7.35 to 7.45.

What if you could shift your body pH?

The body fights VERY hard to keep blood pH in that range, and it’s controlled mainly by the kidneys and by the respiratory system. If the body becomes too acidic (acidosis) or too alkaline (alkalosis) it’s due to either respiratory or metabolic causes. These very serious medical conditions are referred to as metabolic or respiratory acidosis, and metabolic or respiratory alkalosis.Regardless of the hows and whys, if a person’s blood pH varies much from the normal 7.35 to 7.45 range, that person is in big trouble, medically speaking. And what their urine pH is doing isn’t a big part of the equation.

In the end, you cannot push blood or total body pH very hard in either direction with diet alone. The body simply recalibrates, to bring it back to baseline. And what that baseline is may vary from person to person, within that narrow range of approximately 7.35-7.45.

Then what is the role of diet in body acidity and alkalinity?

We do know that over the long term, nutrients such as phosphorus, calcium, and magnesium, all of which can affect acidity, may play a role in specific health conditions. For example, it has long been believed that a diet with too much phosphorus and not enough calcium and magnesium, may contribute to osteoporosis. The theory is that the body pulls calcium from bones for use as a buffer against the acidifying effects of phosphorus, and to help metabolize the excess phosphorus. This is one reason why a phosphorus-heavy diet (processed foods, animal foods, cola-type sodas), had been thought to contribute to bone loss. However, even this theory has come under scrutiny in recent years. Some researchers have shown a higher phosphate diet and more acidic urine may actually decrease calcium and bone loss.

The above example focuses on specific minerals, so let’s return to the general diet question. It is clear that the food-related factor that most impacts acidity and alkalinity – within that very narrow range – is total diet patterns. In general, the more plant-based the diet, the more alkaline the blood and urine tend to be. Overall, animal foods tend to increase acidity, while plant foods tend to decrease it.

There are exceptions – cranberries and plums, for example, tend to increase acidity – but most vegetables and fruit, even if acidic in nature (think citrus), actually create more alkalinity in the body. Research shows that vegans are the least ‘acidic,’ followed closely by vegetarians, and then by omnivores. The bottom line is that eating more plants will make the urine less acidic, and likely, the body less overall as well.

Does it matter why eating more plants decreases acidity?

Personally, I find it convenient that the very same nutrition approach that alkalinizes the urine (and probably the body overall), also is the thing that appears to reduce cancer risk. Available studies in humans support that a plant-based diet – a diet in which the bulk of calories come from minimally processed plant foods including vegetables, fruit, nuts, seeds, legumes, and whole grains – happens to reduce cancer risk and possibly reduce risk of recurrence, and to alkalinize the body.

In the end, if the motivation of acid/base balance helps a person make healthier choices that can simultaneously reduce acidity and reduce disease risk, does it matter? I do believe that why people eats healthier isn’t as important as that they simply do it. Reducing disease risk – cancer, heart disease, obesity, stroke, dementia – is the goal. To make a long story short, if people are interested in ‘alkalinizing,’ it’s helpful to focus on diet patterns.

What about alkalinizing dietary supplements?

I know of a naturopath who recommends his clients who have acidic urine take high, daily doses of magnesium sulfate mixed in selzer water, to “alkalinize” the body. This does alkalinize the urine immediately, though many people who try this end up with loose stools and even diarrhea. Unfortunately, even though magnesium is a mineral that tends to decrease body acidity, it’s not a good idea for most people to take high doses of it over the long-term. Remember milk of magnesia, the laxative? Magnesium is the ingredient that causes the laxative effect.

If you want to increase magnesium intake without the unpleasant side effects, plants are a great solution. In particular, try greens. One serving of spinach, chard, collards, kale, purslane, yellow doc, or other green leafy vegetables has about 2 to 3 times the RDA – now called the Dietary Reference Intake (DRI) – for magnesium.

Back to food

Inevitably, when I explain what we do and don’t know about the relationship between acidity in the body and cancer, I am asked for a list of foods. Which ones are alkalinizing and which foods increase acidity?

Nearly all vegetables, fruit, mushrooms, spices and herbs, and the sweeteners honey and molasses make the urine less acidic. Exceptions include cranberries, plums and prunes, and corn. which tend to make the urine, and possibly the body, more acidic. This doesn’t mean you need to avoid them, because what matters, is the overall dietary pattern. If most of the vegetables and fruit you eat fall in the “alkaline category,” the overall effect will be to alkalinize your urine.

As an example of how a mix of “alkaline” and “acid” foods can still result in less acidic urine, consider vegetarians and vegans. Despite the fact that most grains fall into the “acid food” category, and that most vegetarians and vegans eat plenty of grains, these two groups still have much more alkaline urine than omnivores. Clearly, the fact that the rest of a vegetarian diet is comprised of “alkaline foods,” outweighs the acidifying effect of grains.

Meat, poultry, cheese, fish, eggs, fats and oils, sweets, and most grains (as noted above) are “acidifying,” for the urine at any rate. Milk and dairy are considered neutral to slightly acid. Nuts, seeds, and legumes (beans and peas) are a mix, with some falling into the “acid” category and others being considered “alkaline,” in terms of urine.

It is likely that eating a mix of nuts, seeds, and legumes from each “category of acid/alkaline foods”, on balance, will not significantly alter urine pH. Again, despite the fact that some nuts and legumes are “acid forming,” and that vegetarians and vegans eat large amounts of these foods, these groups of people produce less acidic urine than omnivores. As far as beverages, tea, coffee, vegetable juice and most fruit juices tend to make urine less acidic.

The bottom line

Eating fruit and vegetables is linked with lower risk of all kinds of chronic diseases, including some types of cancer. Most fruit and vegetables are “alkalinizing,” but does this play much of a role in why these foods tend to be protective against chronic disease? We don’t know. It may play some role, but so do phytochemicals, vitamins, minerals, fiber, and the thousands of disease-fighting components found in plants.