A radical rethink of what makes your diet healthy or bad for you

I find myself in the restroom, holding a piece of litmus paper in anticipation. I plan to test my urine and hope that it stays a neutral hue, avoiding any shades of red that would indicate acidity. It’s not a trivial matter; this test represents a personal gauge of whether my dietary habits are detrimental to my health. Acidic urine may suggest an excess in what is termed my dietary acid load, exposing me to numerous potential health issues. The remedy? A simple dietary overhaul. If my findings lean towards the acidic, I will promptly adjust my meals to include more greens, like spinach, and retry. 

Though it may sound like fringe medical advice, there’s an increasing consensus among nutrition scientists that neglecting dietary acid load could be a significant oversight in our approach to healthy eating. “A higher dietary acid load correlates with an elevated risk of chronic illnesses,” explains Hana Kahleova from the Physicians Committee for Responsible Medicine, a Washington, DC-based non-profit research entity. Such diseases encompass kidney and liver maladies, heightened cancer risk, obesity, high blood pressure, and even psychological conditions like anxiety and depression. 

Alarmingly, many of us are mismanaging this issue, particularly those adhering to a conventional Western diet. Conversely, there’s encouraging news: the adverse effects of excessive dietary acid can often be remedied by making informed food choices. The burgeoning research surrounding dietary acid load also sheds light on the links between various dietary patterns and chronic disease occurrences. 

The concept of food influencing the acid-alkaline balance within our bodies took shape in the 1960s, marked by insights revealing that human urine typically manifests acidity, yet the urine of vegetarians leans slightly alkaline. Subsequent studies made connections to the concept of “acid ash” in diets. This previously used measure, known as the acid-ash test, involved burning food items and analyzing their ash, which theoretically mirrored metabolism processes and indicated whether the end products of digestion were acidic or alkaline.

In 1968, research conducted by two Harvard doctors suggested that excessive dietary acid could lead to two prevalent age-related conditions: osteoporosis (bone loss) and sarcopenia (muscle degradation). Their theory proposed that, to counterbalance excessive acid, the body depletes bones and muscles to release alkaline compounds, such as carbonates and phosphates, resulting in decreased bone density and muscle mass. Although the acid-ash hypothesis has since been largely discredited due to lack of evidence linking acidic diets to osteoporosis, the core idea has re-emerged as dietary acid load—a concept reborn from its ashes.  

The principles of measuring acidity are basic chemistry. You probably remember using litmus paper in science class to determine the pH of different substances, ranging from 0 (very acidic) to 14 (very alkaline), with 7 signifying neutrality. In a manner akin to my urine test, litmus paper turns red for acidic substances and blue for alkaline ones. A more intricate version of this analysis illustrates that human blood and its derived tissues maintain a very stable pH, ideally between 7.35 and 7.45, rendering it slightly alkaline overall.  

“Our body requires a consistent pH level,” remarks Kahleova. If the pH strays far from this range, especially dipping below 7.35, it triggers acute metabolic acidosis—a condition characterized by rapid heartbeat, confusion, fatigue, nausea, dizziness, headaches, and, in severe cases, can be fatal. This is unpleasant, but not common. Generally, our bodies effectively maintain pH balance. Common causes of acute acidosis arise from pre-existing medical conditions like kidney and liver disease, cancer, and diabetes, but can also result from extremely high-protein meals, intense exercise, acute diarrhea, or laxative overdoses.  

What raises my acidity?

The primary sources of acid in the bloodstream are CO2 from respiration (which becomes carbonic acid in water) and the acids produced through digestion and metabolism of food and beverages. The lungs manage the former, while the kidneys handle the latter. While carbon dioxide is typically excreted without incident, dietary acids can accumulate based on what we consume, a combined effect known as dietary acid load (DAL).  

To maintain its preferred alkaline condition, our body has to excrete acids on par with those it ingests. When acids outbalance, kidneys excrete the surplus via urine. They can also retain alkaline bicarbonate ions to restore balance in the bloodstream. This system generally works well for most individuals. However, avoiding acute metabolic acidosis doesn’t guarantee optimal health; even hovering around the pH lower threshold (7.35) can lead to low-grade metabolic acidosis—a less critical but still significant health concern.

Determining whether a food is acidic relies not on its plate-side pH but on the pH of its metabolic products. The end products following ingestion vary widely in acidity and can be surprising. Take citrus fruits, for example; while they are deemed acidic, they become alkaline in the body as the citric acid gets converted to bicarbonate during metabolism. Furthermore, they and other plant foods often contain compounds that yield alkaline residues. This contrasts sharply with animal-derived proteins, which are rich in sulfur-containing amino acids that lead to acid production. Many grains and nuts have similar acid-forming impacts. Essentially, proteins are the primary determinants of dietary acid load. Additional notable acid sources include sodium chloride (table salt) and the additive phosphoric acid found in fizzy drinks and various processed products like meats and dairy. 

More risks of a Western diet

At this stage, alarm signals may be going off. Western diets are infamously laden with animal-based foods, salt, refined grains, and ultra-processed options, while being deficient in fruits and vegetables—an ideal scenario for low-grade metabolic acidosis. Researchers believe that this phenomenon is prevalent, if not universal, among those consuming the typical Western diet. “We are all exposed to a consistently high dietary acid load in our diets,” states Ilias Attaye at Erasmus University Medical Center in Rotterdam. 

However, simply transitioning away from a Western dietary framework isn’t a straightforward fix; numerous factors must be weighed. For instance, certain fresh fruits and vegetables contain compounds that metabolize into oxalic acid, making options like beets, blackberries, cherries, grapes, and raspberries less alkaline than one might hope, as noted by Gabriela Leal-Escobar from the Ignacio Chávez National Institute of Cardiology. Moreover, many plant-based processed foods have acid-promoting additives, including phosphoric acid. “You must remain cautious with additives; ensure vegetables don’t have any added substances, as they can significantly exacerbate the acid load,” emphasizes Attaye. 

Another challenge is that determining dietary acid load can be quite complicated. Analyzing urine’s pH levels proves too simplistic for clinical purposes. There’s no universally accepted standard for measuring DAL, but a more refined method exists. The Potential Renal Acid Load (PRAL) method was introduced in the early 1990s to supersede the outdated acid-ash test. This estimation method calculates the expected acid or alkaline output resulting from 100 grams of any food or beverage consumed, reported in milliequivalents per liter (mEq/L). The resulting score ranges from about -15 to +35; lower values denote greater alkalinity, while higher positive values represent acidity, with 0 being neutral. 

PRAL scores are deduced from five nutrient components: protein, phosphorus, calcium, magnesium, and potassium. While protein and phosphorus amplify the PRAL score, calcium, magnesium, and potassium reduce it. This might seem curious, since proteins are pivotal in determining dietary acid load; however, the protein sources come into play. Animal products typically contain higher phosphorus compared to plant-based counterparts, which are generally abundant in calcium, magnesium, and potassium, making animal protein consumers more likely to register higher dietary acid loads.

Typically, foods derived from animals carry acidic PRAL values, while plant-based foods present alkaline scores. “Meats hold a dietary acid load ranging from 8 to 10, while cheese scores around 30, with Parmesan peaking at 34,” states Kahleova. “Rye bread has a measurement of approximately 4, still classified as slightly acidic. Legumes often settle around 0 or a bit negative, while the majority of vegetables and fruits hit negative values—around -4 or -5. Leafy greens lead the way with a score of -14, marking them as optimal for alkalinity.” On another note, alcoholic beverages generally maintain neutral PRAL ratings; wine scores +0.03 per 100 ml, spirits +0.11, and beer -0.2. 

PRAL can be tailored according to individual height and weight, yet it’s not a flawless indicator—notably omitting salt, which may lead to a slight undervaluation of actual dietary acid load. The expectation is that chloride ions derived from salt are mostly linked to processed foods, which many already account for in their PRAL scores. Additionally, since most individuals on Western diets tend to consume similar salt quantities, its effects tend to even out, allowing for general disregard. For everyday references, though, PRAL does provide a useful insight into whether your diet leans acidic or alkaline, contributing to healthier dietary practices.

If you’re curious about acidity in food, there’s no need to compute PRAL from scratch. Helpful tables exist, listing PRAL values for common foods, allowing you to track your daily intake by simply noting down what you eat. A score below 60 mEq/d indicates likely dietary sufficiency, while a negative score—albeit rare in the Western context—is usually harmless. Conversely, exceeding 60 mEq/d is a concern.

In a few days of tracking my own consumption—I found it challenging since the resources only cover raw ingredients—my PRAL score consistently registered around 70 mEq/d. This is mildly better than the average for a typical Western diet. However, as a vegetarian with a penchant for cheese, my score could be improved. Attaye points out that healthy kidneys typically filter out about 40 to 60 mEq of acid each day easily. While they can handle more, it induces significant strain. “They will always find ways to regulate pH,” says Kahleova. However, the excess burden fosters low-grade metabolic acidosis and its related health consequences. 

Initially, the kidneys bear the brunt of this excess acidity. Over time, this leads to gradual impairments, culminating in mild chronic kidney disease. This creates a cycle where impaired kidneys struggle to eliminate excess acid, leading to a consistent burden to maintain pH, potentially resulting in severe acidosis. Nutritional advice often targets low-PRAL diets for individuals already experiencing kidney impairment; however, preventative measures are advantageous. “Reducing the workload on kidneys is beneficial for overall health,” advises Kahleova. 

How acidity harms

There is substantial evidence linking high dietary acid load with renal issues, but emerging research suggests acidic environments may have broader implications. Low-grade metabolic acidosis appears tentatively linked to various chronic conditions, including diabetes, obesity, liver problems, cardiovascular issues, hypertension, cancer, anxiety, and depression. These results are primarily derived from smaller studies, and comprehensive investigations are necessary before DAL can formally inform nutrition guidelines. Excitingly, Attaye has received grants for a study analyzing how varying acid diets impact the metabolic health of individuals with diabetes.

The obesity connection, however, is relatively established. Kahleova’s recent clinical trial with overweight participants revealed intriguing results over a 16-week period, where subjects alternated between a Mediterranean and a low-fat vegan diet. Weight loss differed significantly, with vegan followers shedding an average of 6 kilograms of body fat, not solely attributed to calorie intake reduction. Kahleova found DAL played a pivotal role as well, measuring dietary acidity via PRAL adjustments for weight, noting the vegan diet scored approximately -19.3 mEq/d, contrasting with -1.6 mEq/d for the Mediterranean diet. “An alkaline dietary environment boosts metabolic efficiency; vegan diets elevated metabolic rates, thus increasing total calorie expenditure after meals,” she concludes. 

While other conditions linked to high dietary acid load require more thorough examination, Attaye speculates on a potential mechanism by which acidic diets may contribute to chronic diseases. “Fundamental studies are still underway, so our understanding remains ongoing,” he notes. “But I suspect it may encourage low-grade inflammation.” An overburden on kidneys results in cortisol release, an inflammatory trigger, subsequently posing health risks associated with chronic inflammation. 

Considering the known implications of a high-acid diet, it’s unsurprising that it may also augur a heightened risk of premature mortality. A recent review led by Mohammad Reza Pashaei from Urmia University of Medical Sciences highlights that every incremental rise of 10 mEq/d in dietary acid load correlates with a 3 percent increase in overall mortality risk.

All this paves the way towards a dietary pattern—one both Attaye and Kahleova predict could gain recognition akin to the Mediterranean diet: the low-acid diet. To clarify, it does not align with the spurious alkaline diet rhetoric, which posits that acidity causes cancer and that alkaline diets can thwart or cure it—a notion thoroughly debunked. In 2018, the British Dietetic Association labeled this ideology as “nonsense.” 

A scientifically valid low-acid diet would closely align with general healthy eating principles. There’s a strong correlation between high DAL and guidelines advocating reduced consumption of animal-derived foods, salt, processed items, and an increased intake of fruits and vegetables. “It reinforces the broader narrative of consuming less animal protein, fewer processed foods, and more leafy greens,” Attaye asserts. “Yet, some subtleties exist; it isn’t entirely synonymous, as specific vegetables and grains have an elevated acid load.” 

It has long been recognized that our dietary choices significantly influence chronic disease development. The emerging insights on dietary acid load provide a novel perspective on this connection. “Nutrition is shifting towards a more integrated understanding of food. I believe DAL will play a role in this evolution. It’s not the only lens but an important one,” reflects Attaye.  

Moreover, there’s a tangible takeaway for all of us. The adverse effects stemming from excessive acid-forming food and beverage choices can generally be rectified by opting for more alkaline options. I can personally vouch for this: my initial urine test indicated acidity; however, after consuming a serving of spinach, I tested again and found the litmus paper turned a reassuring blue. 

“This is a matter we can positively influence through our food choices,” states Kahleova. “It’s a straightforward intervention accessible to everyone.”