One of the trends in nutrition (and perhaps vegan nutrition in particular) is the “alkaline diet”, or the idea that we should be eating a balance of “acidifying” and “alkalizing” foods, with an emphasis on those that are “alkalizing”. This practice is supposed to ward off disease, improve longevity, and increase health. We’re told that the more alkaline foods we eat, the more alkaline our entire bodies will become. What these pseudoscientists don’t seem to know is that any dramatic change toward alkalinity (or acidity) would kill you.
Proponents of the alkaline diet will tell you that an alkaline environment in the body will kill cancer cells. That’s technically correct. But what these never-took-highschool-biology pseudoscientists fail to mention is that all your other cells would die too. And so would you.
Our stomach acid (a.k.a. hydrochloric acid) is completely unchanged by the pH level of the foods we eat. And the pH of the digesting food in your intestines has no effect on the pH of the rest of your body. That’s just not how our bodies work. Different tissues have different pH levels. Any variations thereof and you’re in deep trouble.
Many supporters of the alkaline diet will swear by testing our bodies’ pH levels using saliva or urine. Sounds science-y, right? Well, urine pH tests fail to recognize the obvious fact that your urine is contained within your bladder, and has no bearing whatsoever on the pH level of your blood. The pH level of your mouth, similarly, does not reflect the pH levels of the rest of your body.
Most plant-based foods are lumped into the “alkaline” category, and animal products like meat and dairy are categorized as “acidic”. Although animal products may be unhealthy for other reasons (not to mention that they’re immoral to consume and unsustainable to produce), acidity isn’t one of those reasons. An alkaline diet may be good for you because it includes lots of plant-based foods, and an acidic diet might be unhealthy because it contains lots of animal products. This has to do with the nutrient content of these foods, not their pH levels.
There are no human research studies that show benefits of the alkaline diet for the prevention of cancer (one of the diet's main claims), and a distinct lack of studies showing the alkaline diet does much of anything - other than provide health benefits from an increase in foods like vegetables and a decrease in foods like deep-fried stuff. (Duh.)
Bottom line: There's not nearly enough research support out there for you to legitimately start obsessing over "alkaline" or "acidic" foods. It seems that any health benefits seen in people who adopt such a diet come from the nutrient content of foods, not their pH. As usual, this is just another B.S. diet fad.
In this article we're addressing the specific argument we sometimes hear that meat is unhealthy because it “acidifies” our bodies. Is that B.S. too?
Here to give us a rundown of the research that been conducted on this topic is the vegan powerhouse, brain-and-brawn that is Christine Crumbley, PhD.
Christine Crumbley has a PhD in molecular biology. Her research interests include nuclear receptors, regulatory mechanisms of transcription, metabolism, and circadian rhythms. As a scientist and an ethical vegan, she is uniquely positioned to discuss health-related topics. She helps moderate an evidence-based vegan nutrition and fitness group on Facebook, and enjoys researching members' questions to produce new content for the site. Her hobbies include powerlifting, Olympic lifting, baking, volunteering with the local vegan organization, and talking to cats.
The alkaline dietary theory suggests that “acidifying” and “alkalizing” foods should be consumed in “a balance” with an emphasis on consuming alkalizing foods. The acidifying foods include meats, dairy products, corn, wheat, and refined sugars. The alkalizing foods include fruits and vegetables. The alkaline dietary theory proposes that a diet of fruit and vegetables lowers the body’s acid load and reduces stress on the kidneys. The alkaline dietary theory recommends that approved foods are consumed in specific ways, called “food combining,” to reduce acidosis.
There is no evidence for food combining principles to regulate acidosis in humans in the literature, although one study showed that food combining principles did not produce any additional weight loss when calories were reduced equally in a traditional diet and a food combining diet. 
The hypothesis that meat causes cancer because meat is acidic is flawed. The alkaline diet was originally studied in the context of bone health, because an acidic load in the body would, in theory, leech calcium from the bones and reduce bone health. The data showed that acid load from meat did not harm bones, and similar results were obtained with milk. Authors of a 2009 meta-analysis concluded that their study “did not find evidence that phosphate intake contributes to demineralization of bone or to bone calcium excretion in the urine. Dietary advice that dairy products, meats, and grains are detrimental to bone health due to ‘acidic’ phosphate content needs reassessment. There is no evidence that higher phosphate intakes are detrimental to bone health.”  [3-10]
Fruits and veggies are generally associated with reduced cancer risk, but there is no evidence they have to be consumed in any special pattern as proposed by the alkaline dietary theory. I have not seen any papers claiming food combining or other alkaline dietary principles are required for the health benefits of fruits and veggies. If an alkaline diet protects against cancer, then fruits and vegetables should both consistently show protective effects in studies examining cancer risk.
Meat and dairy should be associated with increased cancer risk if the alkaline dietary theory is correct about a food’s acid load and its ability to promote undesirable health effects. For example, colon cancer is commonly associated with meat consumption, but dairy products and calcium appear protective. Both meat and dairy are considered acidic by the alkaline diet theory, but their influences on CRC risk are different. In hepatocellular carcinoma (HCC, liver cancer), it has been suggested that only vegetables have protective effects, but not fruits. In breast cancer, it has been suggested that fruits or the combination of fruits and vegetables are weakly protective, but not vegetables alone. Inconclusive data exists for the effects of fruits and vegetables on bladder cancer risk. Together, these reviews and meta-analyses question the validity of the alkaline diet theory when its two main food groups have different influences on the risk of various cancers. [11-20]
A popular extension of the alkaline dietary theory is that it can be used as a treatment when someone is diagnosed with cancer. There is insufficient evidence for this claim, and more research is needed before the alkaline diet can be suggested as a component of treatment. [21-22]
To address the last part of this claim, omnivores eating plenty of fruits and veggies with small portions of lean meats are likely to have positive health outcomes. This does not seem controversial, especially because the standard American diet does not include much fruit and veggie consumption. This would be where a whole foods vegan diet could have advantages, because vegans would be consuming fruits and veggies closer to the recommended amounts.
“[D]uring 2007–2010, half of the total U.S. population consumed <1 cup of fruit and <1.5 cups of vegetables daily; 76% did not meet fruit intake recommendations, and 87% did not meet vegetable intake recommendations. Median frequency of reported fruit intake across all respondents was once per day, ranging from 0.9 in Arkansas to 1.3 times per day in California. Median frequency of reported vegetable intake was 1.7 times per day, ranging from 1.4 in Louisiana, Mississippi, and North Dakota to 1.9 times per day in California and Oregon. Based on prediction equations, 13.1% of respondents met fruit recommendations, and 8.9% met vegetable recommendations. The percentage of state populations meeting recommendations for fruits ranged from 7.5% in Tennessee to 17.7% in California, and for vegetables, from 5.5% in Mississippi to 13.0% in California.” 
Check out Vegan Bodybuilding and Nutrition, the evidence-based vegan fitness and nutrition Facebook group Christine moderates.
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2. Fenton, T. R., Lyon, A. W., Eliasziw, M., Tough, S. C., & Hanley, D. A. (2009). Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis. Nutr J. 8(41).
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