The Third Dimension of Fruits and Vegetables
The health benefits of a fruit and vegetable based diet are well known, and are most often attributed to their phytonutrient content: vitamins, minerals, flavonoids, phenolic compounds, and fibre. Overlooked in this regard is the role that fruit and vegetable consumption plays in acid-alkaline balance. Fruits and vegetables contain minerals such as potassium and bicarbonate that contribute to the creation of a slightly alkaline state within the body. This is discussed in relation to bone health, cortisol secretion, cancer development and progression, as well as renal function. There is a possibility that supplementation with greens drinks or salts of potassium and/ or bicarbonate can shift the body toward a more alkaline state, and this is supported by preliminary research. Healthcare providers can teach their patients to assess acid-alkaline balance through testing of morning urine; this type of objective testing has the additional benefit of helping patients observe the physiological changes occurring through diet and lifestyle modification, and may help increase long term compliance.
In recent years, government and private sector dietetic organizations have stepped up efforts to encourage the North American population to consume greater amounts of fruits and vegetables. The rationale for this effort is quite clear, it is built upon volumes of international research showing that fruits and vegetables offer a layer of protection against a variety of chronic diseases, most notably cardiovascular disease and cancer (Khaw 2008). The health benefits of dietary fruits and vegetables are generally attributed to two major nutritional aspects – antioxidant (vitamin/ mineral and phytochemical) and fibre content. Indeed, when examined independently, dietary antioxidant and fibre content derived from fruits and vegetables are health protective (Mente 2009). However, there is yet a third avenue of health promotion provided by fruits and vegetables – the underappreciated contribution of dietary bases within fruits and vegetables has assumed great importance in the face of our contemporary, acidheavy diet (Welch 2008).
The pH Scale and PRAL
Acid-alkaline states are reflected on the potential of hydrogen (pH) numerical scale. The scale runs from 1 – 14, with 1 being most acidic and 14 most alkaline. Importantly, since this is a logarithmic scale, moving between each full number (i.e. 6 to 7) represents a 10-fold difference; therefore small changes are not insignificant. The pH of our bodily systems is tightly regulated, operating near the middle of the pH scale. In the blood stream, which operates in the narrow range of 7.35-7.45 (LTO 2013), any deviation away from this near-neutral pH may compromise our very survival. Since the bone matrix contains a relatively abundant alkali reserve in the form of calcium and magnesium cations, it may be called upon to buffer the tightly regulated blood pH in the presence of acidic influences. Today, one of the most consistent acidic influences on pH regulatory systems is the western diet (Berkemeyer 2009).
The notion that diet can play a role in the acid-base balance is not a new one; researchers first showed almost a century ago that meats, dairy, eggs and grains can increase the acidity of urine in humans, while dietary fruits and vegetables can have an alkaline influence on the urine (Sherman 1912). The determination of the acid or base potential of a food or beverage in the human body has advanced with a great degree of sophistication since the early days of subjecting the food to combustion and determining if the ash was acid or alkaline. Today a laboratory test known as the Potential Renal Acid Load (PRAL) has emerged as a reliable indicator of the acid or alkaline potential of a food or beverage in the human body, and is being actively studied by Thomas Remer as a convenient way to estimate the net renal acid excretion due to various food (Remer 1995, 2003). The PRAL model takes into account the following factors in determining the relative acidity of a particular food: “mineral and protein composition of [the] foods, the average intestinal absorption rates of the respective nutrients, sulfur metabolism, and urinary excretion of organic acids” (Remer 1995). Foods and beverages that have potential to contribute to the net acid load in the human body, particularly those rich in proteins and sodium, are said to have a high, or more positive PRAL. Conversely, foods and beverages that are abundant in potassium, bicarbonate and alkaline minerals are said to have a lower, or more negative, PRAL score (Remer 1995). In general, fruits and vegetables consistently have a negative PRAL score (more alkaline), while grains, meats, fish, and dairy products have a positive PRAL score (more acidic). Sometimes foods or beverages patients might consider to be ‘acidic’, such as citrus fruits or tomatoes, are actually quite alkaline in the body due to the presence of minerals and bicarbonates.
Tipping the Scale
The contemporary North American diet contains an abundance of acid-forming foods, particularly animal meats, cheeses, grains, soft drinks and processed foods. Our societal deficiency of fruits and vegetables is obvious: less than 40% of Americans consume the minimum recommended five servings of fruits and vegetables according to a the National Health and Nutrition Examination Survey (NHANES) 1999- 2000 survey (Guenther 2006). Statistics such as this demonstrate widespread deficiency of alkaline minerals and bicarbonates in the American diet, with the scale clearly tipped in favour of acidic foods. Using a computational model, researchers have demonstrated that the mean net endogenous acid production (NEAP) projected for preagricultural, hunter-gatherer diets was -88 mEq/d, compared to +48 mEq/d based on the standard American diet as recorded in the NHANES III study (Sebastian 2002). This increased dietary acid load is not without consequence to human health.
The relationship between acid-rich foods – consumed in the absence of buffering alkaline-rich fruits and vegetables – and the development of osteoporosis is of particular interest to scientists. Since blood pH must remain in a narrow (slightly alkaline) range for survival, calcium and magnesium are removed from the bone to buffer, or neutralize a continuously acidic diet; consequently, calcium and magnesium are drawn into the circulation and excreted through the urine (Rylander 2006). Over time this may lead to an appreciable loss of minerals from the bone matrix. Research does indicate that frequent consumption of high PRAL acid-forming foods (cheese, meats, processed grains) and infrequent consumption of potassium and bicarbonate-rich, alkaline-forming foods (fruits and vegetables) is associated with increased urinary calcium and magnesium loss and a greater risk of osteoporosis (Vormann 2008, Wynn 2008) Scientists have also shown that the bone-forming osteoblasts are less active in acidic environments. Even a modest change to a more alkaline diet has been associated with a 50 percent reduction in fracture risk (Lanham-New 2008).
More recent studies have linked an acidic diet to increased body weight, increased waist circumference (Berkemeyer 2009, Remer 2007) and various markers of cardiovascular disease, including elevated cholesterol and hypertension (Murakami 2008). Recently it was reported that adults with metabolic syndrome are likely to have more acidic urine than adults without metabolic syndrome (Maalouf 2007). On the other hand, more alkaline urine is associated with a greater percentage of lean body mass (Dawson- Hughes 2008). In addition, a more alkaline diet rich in potassium was found to improve mental outlook and energy in otherwise healthy adults (Torres 2008).
The Cortisol Connection
Swiss researchers discovered an important physiological change induced by an acidic, fast-food-type diet, a change with enormous implications for human health: consuming an acidic, Western-type diet for nine days was shown to significantly elevate the stress hormone cortisol. When the researchers neutralized the Western diet with bicarbonate supplements, the cortisol levels dropped down to normal (Maurer 2003). Since cortisol increases the propensity to gain abdominal fat, promotes inflammation and oxidative stress, disturbs immune function and mood states (Epel 2009), this research makes pH an important consideration in human health. The lesson in this research may be less about acid foods themselves, and more about the importance of neutralization with our absentee fruits and vegetables.
For years an avoidance of acidic foods has been advocated for reducing cancer risk, malignancy and recurrence. Indeed, the possibility of acidic meats rich in sodium promoting cancer was first hypothesized more than a century ago (Braithwaite 1901). While supporting the protective role of fruits and vegetables in cancer, the American Institute for Cancer Research (AICR) recently scoffed at the notion of any connection between acidic foods and cancer (AICR 2008). Several lines of research indicate that further investigation is required, however, and the preponderance of recent evidence suggests that there may indeed be a connection. First, more alkaline urine has been noted to enhance the excretion of a variety of xenobiotics in a process known as ion trapping at the kidney. In the presence of more alkaline urine, certain environmental toxins and drugs existing as weak acids are more readily excreted and reabsorption by the renal tubules is inhibited (Minich 2007).
Given that alkaline, mineral-rich, drinking water can influence urinary pH, there has been surprisingly little research into the connection between the pH of municipal water and cancer rates. The only studies conducted so far, three separate investigations in Asia, found that rates of esophageal, rectal, and pancreatic cancer mortality rates are all significantly lower in regions where municipal water pH is more alkaline (Yang 1999a, Yang 1999b, Yang 1999c). Use of soft water was associated with a 42% increased risk of esophageal cancer (adjusted OR 1.42, 95% confidence interval 1.22-1.66) (Yang 1999a), 38% increased risk of rectal cancer (AOR 1.38, 95% CI 1.10-1.73) (Yang 1999b), and 39% increased risk of pancreatic cancer (AOR 1.39, 95% CI 1.09–1.76) (Yang 1999c). In addition, Russian researchers reported that among 150 patients recovering from gastric cancer, those consuming alkaline mineral water had approximately 3.8-fold reduced recurrence rates, while 300 breast cancer patients postmastectomy had a 20% reduction in recurrence, though unfortunately further details were unavailable due to language limitations (Vladimirov 2004).
Secondly, the research showing that the typical acid-heavy North American diet can increase cortisol, and that neutralization of the same acidic diet with bicarbonate can reduce cortisol in humans, is also of great relevance to cancer. In animal studies, elevations in cortisol is associated with rapid growth of tumors, and in human depressive disorders, characterized by hypercortisolemia, a more rapid breast cancer progression has been noted in 19 out of 24 studies (Palesh 2007). Various aspects of the immune system are compromised with chronic cortisol elevation (Epel 2009). It is also true that a shift toward a more acidic environment diminishes the functionality of natural killer cells and promotes the production of inflammatory cytokines (Kellum 2004, Lardner 2001).
The most convincing evidence comes from direct studies of the pH of cancer cells and their surrounding environments. A number of recent studies using pH sensitive magnetic resonance imaging contrast agents and microelectrodes have consistently shown that the extracellular pH of tissue surrounding tumors is significantly lower than that of healthy tissues (Bellone 2013, Estrella 2013). A low pH microenvironment is now known to increase the growth and invasiveness of tumor cells in vivo. Bathing tumor cells in an acidic pH (6.7, typical of the extracellular pH of tumors) increases invasiveness by 4-fold (Silva 2009).
Discounting test-tube studies in cancer and acidbase balance, the AICR stated that “altering the cell environment of the human body to create a lessacidic, less-cancer-friendly environment is virtually impossible” (2008). Yet, emerging studies are at odds with this claim. In recent animal investigations oral bicarbonate has been shown to increase the extracellular pH of tumors, subsequently reducing the in vivo number and size of tumor metastases. Ultimately the reductions in metastases after oral bicarbonate led to increased survival rates of the animals with tumors (Robey 2009). Importantly, the chronic administration of bicarbonate produced no change in the tightly regulated blood pH, indicating that the results were based on a local buffering phenomenon via the oral alkaline solution. This provides more than mere speculation that the reverse would also be true, i.e. that chronic consumption of oral diet-derived acids can influence the interstitial fluid of primary and/or metastatic tumors in the absence of significant changes to blood pH. While much more research is needed, for now the only myth concerning acid-alkaline diet and cancer is that which states there is no relationship between the two.
Chronic Kidney Disease
A fourth area within medicine that is being studied with respect to acid-base balance is chronic kidney disease, though in this case the population has already progressed from subacute acidosis (Kovesdy 2012). Nonetheless, it is of relevance that in this context, supplementing with alkali may be able to slow the loss of renal function. A study by de Brito-Ashurst et al found that supplementing 134 patients with reduced baseline creatinine clearance (15–30 mL/min) with oral sodium bicarbonate tablets 600mg three times daily, titrated to achieve target serum bicarbonate levels of ≥23 mEq/L, resulted in a slower slope of progression for creatinine clearance and fewer incidences of rapid loss of kidney function and end stage renal disease (defined as creatinine clearance <10 mL/min), compared to usual care (2009). Other studies have shown similar findings, with slower decline in eGFR and decreases in urinary endothelin-1, albuminuria, and tubular injury markers (Kovesdy 2012, Phisitkul 2010).
What to Do?
When a daily diet with a high net acid load becomes the rule rather than the exception, it sets the stage for what has been described as a chronic low-grade level of metabolic acidosis. This, in turn, may be influencing a number of different health outcomes. Therefore, in the clinical setting it is important to establish a baseline of acid-alkaline status in the body. Urinary pH has been established as a reliable surrogate marker for the state of acid-alkaline balance in the human body (Welch 2008), and while 24-hour urinary pH is the gold standard, it may be worthwhile to have patients measure the first morning urine after an overnight fast for 7-10 days. It may also be prudent to have a discussion with patients concerning the meaning of the pH scale itself, reminding them that small changes in the numerical value are of significant importance. For patients the measurement of pH is an inexpensive investment; commercially available litmus paper provides an accurate assessment of pH, equal to that of the dipsticks used by clinicians (Desai 2008).
The obvious clinical priority is to provide the standard advice to consume an abundance and broad variety of fruits and vegetables. Concomitant reduction of meats, dairy and grains will help reduce the net acid load. Reframing the advice away from fibre and antioxidants, moving in the direction of pH may provide a novel stimulus to comply with the healthy change, particularly when provided in the context of a simple urinary test that may enhance goal-oriented motivation. Supplementation is also an option. Recently researchers from the University of Toronto showed that a commercially available supplement with dehydrated plant foods (greens+) can influence urinary pH. The pH of first-morning urine was made significantly more alkaline in otherwise healthy adults after 14 days, particularly among those with more acidic urine pre-supplementation (Berardi 2008). It has also been shown that supplementation with potassium citrate and bicarbonate can influence urinary pH in the direction of alkalinity (Minich 2007).
While the science of net dietary acid load has advanced in recent years, the clinical utility of addressing the acidbase balance is not a recent phenomenon. The notion that frequent consumption of acid-heavy foods can promote inflammation is also not a new concept, nor is the use of diet and bicarbonate supplements to address health. In the 1920s dermatologists reported that alkaline ash foods and bicarbonates were helpful in lowering skin inflammation – “In nearly all cases, active inflammatory processes cease and the eruption rapidly clears when the urine is rendered alkaline” (Ormsby 1920). The acidbase connection to human health requires much more study, since for now there are still more questions than answers. Hopefully in the near future we will have a greater understanding of the mechanisms surrounding the net dietary acid load and its influence on cortisol, interstitial pH, detoxification and our immune systems. The collateral health benefits provide more than enough justification for an emphasis on potassium, bicarbonate, and mineral-rich fruits and vegetables.
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