The Acid/Base Diet was developed when a French biologist discovered that changing rabbits’ diets from an herbivorous to a carnivorous one resulted in a change in their urinary pH, which is a measure of acidity. As omnivores, humans’ urinary pH ranges from acidic to alkaline but is generally close to neutral. It has been theorized by some that a diet high in acid-forming foods encourages the breakdown of bone in order to return blood pH to normal. This, in turn, leads to osteoporosis and the theory that the acidic environment created by the acid-forming foods predisposes one to both kidney stones and cancer.
Can an Alkaline Diet Prevent Cancer?
So far, meta-analyses have found no correlation between dietary acid and bone health – alkaline diets are not terribly helpful with cancer nutrition. In addition, there have been no studies supporting the acid/base diet as protective against cancer. It has been observed in test tube studies, however, that certain cancers may grow faster in acidic solutions and some chemotherapy drugs may be more effective in alkaline environments. These observations have not been tested in humans, so no further assumptions can be made.
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.
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 [i][ii].
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 [iii].
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, or other green leafy vegetables has about 2 to 3 times the RDA – now called the Dietary Reference Intake (DRI) – for magnesium.
Back to Alkaline Food
Inevitably, when I explain what we do and don’t know about the relationship between alkalinity 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.
Alkaline Diet: Is it safe?
Some Acid/Base Diet advocates advise testing the pH of your saliva or urine to determine the overall acid/base balance of your body, but this is not a good indicator. The fact is, the human body does not function as one unit; different organs function better at different pH’s. It is impossible to manipulate your body’s pH to any extreme and by doing so can place additional stress on you renal and respiratory systems to accommodate the Acid/Base Diet. In fact, diet can at most only very slightly and temporarily alter your body’s pH.
Other risks associated with the Acid/Base diet include:
- Encourages the consumption of large amounts of alkaline-forming food and the restriction of acid-forming food. These recommendations can contribute to deficiencies of protein, essential fatty acids, vitamins, Calcium, fiber, and phytonutrients.
- While most vegetables are allowed on this diet and processed foods, sugar, caffeine, and alcohol are discouraged, there are limitations regarding which seeds, nuts, grains, beans, peas, meat, fish, dairy, fruits, and fats are permitted because of their acidity. These restrictions can limit the beneficial cancer-fighting phytonutrients and antioxidants in these foods.
- The lack of scientific evidence for the effectiveness of the Acid/Base Diet and the potential for malnourishment discourage many Registered Dietitians from recommending this diet to their clients. The American Institute for Cancer Research has also labeled the Acid/Base Diet and its underlying theory a myth.
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 [iv].
In the end, if the motivation of an alkaline diet 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.