Dietary Acid Load: From Kimball C Atwood, the Father of Functional Food, to Contemporary Science
Abstract
Much has been written about the “alkaline diet” in the lay press. Proponents suggest it is a cure-all for endless lists of human ailments. Critics suggest that since acid-base balance is so tightly regulated, the acidity or alkalinity of diet is, with only few exceptions, of little relevance to human health. This review explores early origins of the marketing of the acid-alkaline diet and reflect its rudimentary science off a more sophisticated, contemporary understanding of dietary acid load. As outlined here, the North American alkaline diet phenomenon was manufactured by grapefruit mogul and food faddist, Kimball C Atwood. The marketing techniques initiated by Atwood—using the trapping of science to promote a healthy idea to the masses—were highly lucrative and imitated by many other companies. However, by using the ornamentation of science, Atwood set in motion a century of confusion regarding the legitimacy of the acid-alkaline diet and the importance of dietary acid load in the prevention or management of chronic illnesses. Understanding this history allows naturopathic doctors to appreciate the reasons why confusing and contradictory media headlines related to acid-alkaline diets endure. The reasonable notion that dietary acid load and low-grade acidosis matters to various aspects of health—that it is neither a con nor a cure—is backed up by volumes of emerging science.
Introduction
Life on Earth has evolved under the influence of the potential of hydrogen (pH) within natural environments. For example, flourishing marine ecosystems have enjoyed a relatively stable ocean pH for millennia; however, rapid changes in the industrial age have already produced anthropogenic shifts in the pH of ocean water, threatening life within the marine ecosystems (Linares et al 2015, Pelejero et al 2010). In agricultural ecosystems, plant growth, and the presence of soil microbes that have a beneficial influence on plant growth, is determined by soil pH; the abundance and diversity of bacteria are increased along a pH range from acidic to slightly alkaline, and soil acidification, a threat to crop growth, is offset by various techniques in agriculture (Rousk et al 2010). Humans, of course, are no exception to the rule of hydrogen ion regulation; the pH of bodily systems is tightly regulated. For example, deviations from a very narrow 7.36-7.44 blood pH are considered an ’emia’ (acidemia/alkalemia) and can present a threat to survival (Quade et al 2021).
The idea that specific dietary patterns and foods can put pressure on the tightly regulated pH within the blood and extracellular spaces has been contentious. In the first part of the 20th century, physicians placed a good deal of clinical emphasis on the pH of urine as a surrogate marker for various ailments; while the dangers of acidosis and alkalosis were well known, a tendency toward a more acidic urinary pH was much more frequently attached to chronic disease states. The general public responded to the emotional meaning of the word acid (from Latin acerbus (bitter); acidus (sour); acer (sharp)) and its perceived ‘corrosiveness’ to health; the notion of acid-base ‘balance’ was more likely to provided inner meaning and security to the lay consumer of information (Manz 2001).
The paper reviews the early origins of the marketing of the acid-alkaline diet and reflect its rudimentary science off a more sophisticated, contemporary understanding of dietary acid load. As outlined here, the North American alkaline diet phenomenon was initiated by grapefruit mogul and food faddist, Kimball C Atwood. Understanding this history allows the reader to appreciate the reasons why media headlines such as “The Alkaline Diet – Con or Cure?” (Walker 2011) endure. A century after Atwood invented the alkaline cure, Robert O Young, an uncredentialed “naturopathic practitioner”, wrote the international bestselling “pH Miracle!” (Young and Young 2002) which was translated into 18 languages. Young would eventually be convicted of practicing medicine without a license after he promoted cancer cures and set up alkaline intravenous treatments at $500USD per session (Figueroa 2017). The promotion of an alkaline diet as a “cure” or “miracle” is obviously not part of contemporary naturopathic training; however, the reasonable notion that dietary acid load and low-grade acidosis matters to various aspects of health—that it is neither a con or a cure—is backed up by emerging science.
Father of Functional Food and the Super Fruit
Early enthusiasm for the role of acid-alkaline influences and diet in health can be traced to Kimball C Atwood (1853-1936); Atwood was an influential entrepreneur who made heavy investments in Florida’s undeveloped west coast. In the early 1900s he transformed thousands of acres of land in Manatee County into the largest grapefruit grove in the world. At the time, widespread availability of grapefruit was limited. Atwood’s challenge was how to sell those grapefruits and get a return on his massive investments. He decided upon an aggressive marketing campaign focused on the wide-ranging health benefits of grapefruit, and more specifically to promote it as “The New Cure” for disease. In his words: “Nature has responded to the world-wide cry for relief from a distressing malady by appealing to the palate in a most seductive way” (Atwood Grape Fruit 1910A).
Of course, patent medicines and botanical nostrums had long been sold for ailments from A to Z. However, Atwood broke from this tradition and chose a single dietary item and promoted its multidimensional healing properties. Seizing on the fledgling clinical interest in manipulating urinary pH to promote health, Atwood developed a three-pronged marketing campaign to sell his grapefruits. First, he touted physician support for the food. For example, “A prominent physician of New Haven prescribes [grapefruit] for all his patients, telling them be sure to get the ATWOOD” (Atwood Grape Fruit 1909); second, Atwood described the curative properties from diseases and disorders, and more generally for increased “energy”, to “renew their youth” and inferences that it improves sleep (“taken at night on retiring it is better than drugs”) (Scribner 1909); third, he provided at least one key mechanism of action by which the grapefruit could cure diseases and promote health – that is, by “rendering an unduly acid urine alkaline” (Atwood Grape Fruit 1910B).
The marketing campaign was directed at physician journals and the lay press. Indeed, Atwood paid for block advertisements in journals such as American Medicine. Perhaps delighted with his advertising support, the editors of American Medicine wrote a favorable review of grapefruit for health which Atwood subsequently recycled and quoted within his advertisements in the more prestigious Journal of the American Medical Association (JAMA) and in dozens of other journals and magazines; the JAMA ad states: “American Medicine says: ‘Realizing the great value of grapefruit, the medical profession have long advocated its daily use, but it has only been in the past few years that the extraordinary curative virtues of this ‘King of Fruits’ have been appreciated. This dates from the introduction of the ATWOOD Grape Fruit, a kind that so far surpasses the ordinary grape fruit that no comparison can be made” (Atwood Grape Fruit 1912). Atwood also incorporated the testimonial of Edward E Keeler, a medical doctor and homeopath, who wrote glowingly of the grapefruit in his popular book “Here’s How Health Happens” (Keeler 1912).
Remarkably, Atwood not only simultaneously promoted the grapefruit cure and alkalinity, he also informed the advertisement reader on the extent of his financial investments in ‘science’. For example, the half-page advertisement in New England magazine (1910) reads: “Physicians [have found] that only ATWOOD Grape Fruit can be depended upon to impart [the] properties so beneficial to persons of acid natures, especially sufferers of rheumatism… The ATWOOD Grove, at Manavista, Florida, where 250 acres are devoted to its scientific cultivation at an initial expenditure of over a quarter of a million dollars” (Epicures 1910).
In sum, Kimball C Atwood promoted grapefruit as a food for function and separated it from other fruits as the ‘king’; he injected physician testimonials and positioned the curative fruit as the subject of medical and scientific investment. The ability of this super fruit to render the urine alkaline was a central part of the message. Atwood’s return on marketing investments was tremendous; his methods of advertising in magazine and journals were so successful that media wrote headlines such as “How Atwood Sells His Fruit” (Bittinger 1910), “To Advertize Grapefruit” (Harris 1906), and “A Selling Plan for Grapefruit” (Editors 1910). The latter story reported that Atwood recuperated $3 dollars in profit for every $1 invested in his aggressive marketing. The next wave of Atwood’s marketing campaign, exemplified by these words in an advertisement in the American Journal of Clinical Medicine, broadened and reinforced the medicinal properties of the fruit: “Last season we placed emphasis on the curative value of citric acid as found in the ATWOOD Grape Fruit. With the first suggestion of the use of this grapefruit in rheumatic and febrile conditions came a quick endorsement from physicians and the public…in a class by itself when used either as a luxury or medicinally…everything that science and experience was done” (Atwood Grape Fruit 1911).
The place of Kimball C Atwood in the annals of medical history and health marketing isn’t merely a matter of intellectual curiosity; he greatly increased the public’s interest in the “acid-alkaline” diet and the idea that there are ‘functional’ foods and super fruits; competitors who had been quietly selling oranges as a mere commodity were astonished at the public uptake of Atwood’s advertising, commenting that he had driven unprecedented levels of demand over mere months compared to their efforts over years. His grapefruit cure campaign was lengthy – a decade after it began, Atwood was still placing block advertisements in magazines directed at women (Atwood Grape Fruit 1918). Put simply, Atwood was a catalyst in spreading the idea that ‘acidity’ matters. He pushed the notion onto physicians and in a circular system, pulled it from them. As a matter of historical interest, it is worth pointing out that Benedict Lust, widely held to be the founder of naturopathic medicine in North America, was a rival of Atwood; Lust had his own grapefruit groves two hours away, in Tangerine, Florida. Lust marketed his grapefruits as a cut above in quality (Lust 1916).
Atwood’s highly effective marketing campaign predated the first thorough attempts to identify the acid-base forming elements in common foods by several years; Henry C Sherman, who would go on to become the president of the American Institute of Nutrition and the American Society of Biological Chemists, and colleagues provided the first comprehensive study of 47 different foods – and the biological effects of consumption – in 1912 (Sherman and Gettler 1912). In the years following Atwood’s marketing campaign, scientists and medical doctors in North America and Europe provided case reports supporting the use of specific diets that were purported to be ‘alkaline’. For example, it was reported that the incorporation of alkaline foods reduced cutaneous inflammatory lesions (Kroetz 1930, Umrath 1943). Researchers in dermatology concluded that “In nearly all cases, active inflammatory processes cease and the eruption rapidly clears when the urine is rendered alkaline” (Ormsby and Mitchell 1920). By the late 1930s, an alkaline diet was recommended for inflammatory skin conditions such as eczema (Hellier 1938). However, there were mixed findings in the research (Ingram and Fowweather 1931, Whitfield 1934) and the validity and relevance of the acid-alkaline food lists was questioned (Bischoff et al 1934); milk company scientists seemed especially sensitive, claiming that the acid-alkaline diet was a major part of food fads promoted by “quacks and ignoramuses and religiously followed by a host of deluded persons” (Tobey 1936). By the 1960s, outside of metabolic acidosis or kidney disease, the acid-alkaline diet was dismissed as being of little relevance to clinical nutrition (Brady 1959, Ewalt 1959).
Dietary Acid Load
The acid-alkaline diet concept emerged again in the 1970s. In 1969, two physician/scientists writing in the Lancet proposed that osteoporosis may, to some degree, be related to the dominance of acidic foods (or the absence of alkaline fruits and vegetables) in the western diet. They proposed that in the context of a continuous acidic, western diet, the tight regulation of blood pH necessitates miniscule amounts of alkaline salts to be removed from bone as a buffering source. They suggested that over time this could add up to meaningful losses—as much as 15% of inorganic bone mass in an average individual over a decade (Wachman and Bernstein 1968). Until the end of first decade of the 21st century, there was little evidence to support the theory. However, as discussed below, new evidence has substantiated the hypothesis.
One of the potential factors behind the inconsistency of findings related to early acid-alkaline diet interventions, and the topic in general, was related to the inaccuracy of lists of supposed acid and alkaline foods and beverages. Early on, the determination of the acid or base potential of a food or beverage in the human body was based on subjecting the food to combustion and determining if the ash was acid or alkaline (Dwyer et al 1985). However, the laboratory test known as the potential renal acid load (PRAL), developed in 1995, is now recognized as a reliable indicator of the acid or alkaline potential of a food or beverage in the human body. Foods and beverages rich in proteins and sodium are said to have a high, or more positive PRAL. That is, they are considered to be acidic in the human body. On the other hand, foods and beverages that are rich in potassium and alkaline minerals with the potential of forming bicarbonates are said to have a lower, or more negative, PRAL score (Remer and Manz 1995). Citrus fruit as promoted by Atwood is definitely in the negative range; the consistent theme is that fruits and vegetables are alkaline (negative PRAL), meats, hard cheeses and grains are acidic (positive PRAL), and milk and yogurt are mildly acidic. PRAL scores are a reliable marker of dietary acid load and shifts in urinary pH reflect PRAL-associated dietary patterns (Remer et al 2003).
While the acidic diet osteoporosis theory has been historically contentious, recent studies clearly demonstrate that an alkaline diet (plant-based, low-PRAL) and dietary alkaline supplements are capable of increasing urinary pH, blood pH, and/or blood bicarbonate concentrations (Cosgrove and Johnston 2017, Hottenrott et al 2020, Limmer et al 2020). Well-designed studies published in the last five years provide evidence that high PRAL and net endogenous acid production (NEAP) are negatively associated with bone mineral density, and positively associated with frailty and fracture risk (García-Gavilán et al 2021, Hayhoe et al 2020, Kataya et al 2018). The findings are bolstered by studies that have linked fruit intake and serum bicarbonate levels to bone mineral density in older adults (Liu et al 2015, Tabatabai et al 2015), and alkaline salt (potassium) interventions or potassium-rich dietary patterns that show a favourable influence on bone health (Cao et al 2021, Granchi et al 2018, Ha et al 2020, Moseley et al 2013).
While the connections between dietary acid load and bone health continue to strengthen, there has been a robust growth in research linking dietary acid load to multiple chronic non-communicable diseases. In the last five years, dietary acid load has been associated with type 2 diabetes (Akter et al 2017, Kiefte-de Jong et al 2017), insulin resistance (Caferoglu et al 2021, Gæde et al 2018, Lee and Shin 2020, Moghadam et al 2016), obesity (Abbasalizad Farhangi et al 2019), cardiovascular disease and associated lipid risk factors (Arisawa et al 2020, Han et al 2016, Jafari et al 2021, Mazidi et al 2018), hypertension (Banerjee et al 2021, Krupp et al 2018, Murakami et al 2017), hyperuricemia (Esche et al 2018, Shin and Lee 2021), kidney dysfunction (Mirmiran et al 2016, Rebholz et al 2015, So et al 2016), breast cancer (and prognosis) (Park et al 2019, Wu et al 2020A), pancreatic cancer (Shi et al 2021), lung cancer (Ronco et al 2021), colorectal cancer (Jafari Nasab et al 2021), migraine headaches (Mousavi et al 2021), and mortality (Akter et al 2017). Discussed in further detail below will be the remarkable new studies linking dietary acid load to mental disorders. With so many non-communicable diseases linked to dietary acid load, it should be expected that there should be one or several common mechanisms of action. As discussed below, the idea that, in the context of our evolutionary past, the acidic westernized diet is a metabolic stressor, is one unifying concept.
Acidic Diet as a Stressor
The theory that a consistently acid westernized diet places a burden on the skeletal system (a reservoir of alkaline minerals) has provided a relatively sound mechanism of action for links between diet and osteoporosis; however, until recently, mechanistic links between dietary acid load and many diverse medical conditions have been elusive. In a 2003 study by Swiss researchers, a specific physiological change induced by a high-acid load, fast-food type diet was discovered. Consumption of an acidic, western-type diet for nine days significantly elevated the stress hormone cortisol. When researchers neutralized the diet with bicarbonate supplements, even while subjects maintained the high-acid-load diet, the cortisol levels were reduced significantly versus controls maintaining the western diet (Maurer et al 2003). Similar clinical studies have since demonstrated the ability of oral alkaline supplements to neutralize elevations in glucocorticoid activity (Buehlmeier et al 2016, Conen et al 2016). In children, increased fruit and vegetable intake has been associated with lower urinary glucocorticoids (Esche et al 2015, Esche et al 2016).
Essentially, an acidic, westernized diet, largely devoid of potassium, bicarbonates and other alkaline-rich fruits and vegetables, is a metabolic stressor. In the context of our evolutionary past, such a diet is relatively novel and may present a ‘mismatch’. Since subclinical hypercortisolism with chronic, mild cortisol excess is frequently related to hypertension, and is also characteristic of obesity, cardiovascular disease, lipid disorders, type 2 diabetes, lower skeletal muscle mass, various mental disorders, and osteoporosis, the implications to healthcare are significant (Di Dalmazi et al 2015, Herane-Vives et al 2018, Kim et al 2018, Min 2016, Ortiz et al 2019). In line with this research is the recent finding that higher dietary acid load is associated with C-reactive protein (CRP)— compared to women with the lowest quartile of dietary acid load, women with the highest quartile showed 30–33% higher levels of CRP (Wu et al 2019). The relationship between dietary acid load, glucocorticoids, and inflammation, now replicated in several studies, represents at least one important unifying mechanism whereby the absence of alkaline-rich plant foods can be related to multiple chronic non-communicable diseases.
Dietary acid load has recently been linked to depression, anxiety, and other mental disorders (Daneshzad et al 2020, Milajerdi et al 2020, Mozaffari et al 2020, Wu et al 2020B). For example, depressed women with a dietary acid load higher than median reported 2.75 times the risk of reduced physical function and 3.10 times the risk of poor physical health compared to non-depressed women with a dietary acid load lower than median (Tessou et al 2021). Children with high PRAL dietary patterns have been found to have more overall emotional problems, and hyperactivity in particular (Bühlmeier et al 2018). Even a short-term (two week) high-potassium/low-sodium dietary intervention has been shown to improve mood compared to control diets (Torres et al 2008).
Additional mechanistic pathways involve alteration of the gut microbiome. For example, alkaline water, compared to tap water, has been shown to increase the growth of Bifidobacterium (Tanaka et al 2021). Emerging clinical research demonstrates value of alkaline water in irritable bowel syndrome (Shin et al 2018); animal research suggests that alterations in microbial tax may be at least one mechanism by which the alkaline water positively influences the intestinal ecosystem (Higashimura et al 2018).
Gone are the days when dietary acid load and acid-base balance can be dismissed as irrelevant. In 2021, the results from the Golestan Cohort Study with over 50,000 participants showed that acid and alkaline balance are important to cardiovascular and all-cause mortality. The researchers concluded that “it may be important to consider a balanced acid-base diet as a protective strategy to prevent pre-mature death, especially from cardiovascular disease” (Hejazi et al 2021). Recent randomized controlled trials demonstrate that plant-based diets significantly reduce dietary acid load (Kahleova et al 2021, Müller et al 2021).
Cancer Controversy
Among the lay public, the concept of dietary acid load is most often discussed in relation to cancer prevention and/or treatment (Walker 2011). In recent years, a spate of trade paperbacks have been published with titles promising the prevention, cure and/or management of cancer by an alkaline diet (Doris 2020, James 2020, Josh 2021, Philip 2021). Despite the epidemiological links between dietary acid load and cancer, there is at present no research that shows that specific dietary interventions are helpful in oncology by virtue of an alkaline potential. At the same time, the widely touted skeptical claim that the systemic microenvironment surrounding tumors cannot be altered by oral alkaline interventions, has itself been debunked. In animal models, researchers have proven that oral bicarbonate, without changing blood pH, can increase the extracellular pH of tumors. The reduced acidity at the local level subsequently decreased the in vivo number and size of tumor metastases, as well as survival (Robey et al 2009). Recently, low levels of serum bicarbonate have been associated with higher levels of systemic inflammation and lower short-term survivability in post-operative adults with colorectal cancer (Chan et al 2020). The use of bicarbonate and other alkaline-based interventions to treat cancer is currently an area of intense scrutiny by oncology researchers (Ando et al 2021, Wang et al 2021).
This exciting work should not be confounded, as it often is by the lay public and those promoting profit-based books and over-the-counter products, with an alkaline diet cure. In 2021, the website Plant Based News reported the case of a cancer cure through an alkaline diet intervention, but that story was subsequently retracted by the outlet (Baker 2021).The story and its retraction encapsulate an ongoing controversy that is nearly a century old. For now, the benefits of promoting a diverse, colourful, fibrous diet dominated by polyphenol-rich fruits and vegetables to the wellbeing of all individuals, including those with a history of cancer, with current cancer, or in remission, are obvious and many.
Conclusion
The idea of the industrial diet as harmfully acidic, and a functional superfruit to provide a healthy alkaline offset, belongs to citrus mogul Kimball C Atwood. The marketing techniques initiated by Atwood—using the trapping of science to promote a healthy idea to the masses—were highly lucrative and imitated by many other companies. However, by using the ornamentation of science, Atwood placed a decorative horse before the grapefruit cart, and set in motion a century of confusion regarding the legitimacy of the acid-alkaline diet and the importance of dietary acid load in the prevention or management of chronic illnesses. Despite volumes of recent scientific evidence on the importance of dietary acid load, and the mechanisms linking it to chronic disease (and dis-ease), the concept is still dismissed in some quarters as a fad.
Knowledge of the importance of acid-base balance and the consequences of metabolic acidosis or metabolic alkalosis is an important part of medical training. In 2021, an editorial in BMJ Open Heart stated that low-grade acidosis, the version induced by the westernized diet, is a “21st century public health crisis” requiring greater emphasis in medical schools (DiNicolantonio and O’Keefe 2021). Naturopathic doctors are well-versed in the topic, and accountability can be found in required testing in both basic science and clinical exams. At the same time, naturopathic doctors have been keen observers and clinical specialists in the rational center of a long continuum—between the poles of miracle cures at the one end, and outright dismissal of the acid-base balance by dairy board propagandists at the other. As the evidence mounts on the relationships between dietary acid load, chronic low-grade acidosis/hypercortisolism, and chronic non-communicable diseases, naturopathic doctors are ideally positioned to provide clinical guidance.
Beyond the clinic, it is important for our profession to separate ourselves from the pseudoscience associated with “alkaline diets” touted to cure long lists of ailments and “melt the pounds away”. The 2017 sentencing agreement in the State of California vs. Robert O Young, the international celebrity of the alkaline diet, was that he make a public admission “declaring that he is not a microbiologist, hematologist, medical or naturopathic doctor or trained scientist” (Figueroa 2017). As licensed and trained naturopathic doctors, it is vital that we understand the borderland between Kimball C Atwood’s superfood marketing, and the emerging science that can promote the health of our patients and communities.
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