Skepticism
Before writing this blog post, I had vaguely heard of dietary acid load but was inclined to believe that it was nonsense. I’m not sure how came to believe that. After reading a number of articles, I changed my mind. Evidence to date shows that dietary acid load affects your health and well-being. Plus, reducing your dietary acid load seems to be relatively straightforward, as you’ll see.
What is dietary acid load?
During the digestive process, the food you eat undergoes a number of biochemical processes that affect your body in many ways. One of those ways is the balance between acidity and alkalinity of your blood. That balance is measured as the pH, pronounced “pee-aich.” The pH scale runs from 1 to 14, with numbers less than 7 denoting acidic conditions, while numbers more than 7 denoting alkaline conditions. The pH of blood is tightly regulated around an average value of 7.25. Even slight variations above or below this point cause problems. The digestive process creates acidic chemicals from some foods (generally meat, dairy products, ultra-processed foods) and alkaline chemicals from other foods (generally fruits, vegetables, legumes, nuts). Thus, dietary acid load reflects the relative amounts of acid-forming foods and alkaline-forming foods. A diet heavy in meat, dairy, and ultra-processed foods will have a higher dietary acid load, while a diet heavy in fruits, vegetables, and legumes will have a lower dietary acid load.
Why is dietary acid load important?
As you’ll see, diets with higher dietary acid load predict increased risks of serious health problems. The list includes greater risk of premature death, cardiovascular disease, hypertension, impaired bone health, type 2 diabetes, kidney disease, the metabolic syndrome, kidney stones, and certain cancers.
Premature death
Japanese researchers wondered if diet-induced metabolic acidosis would predict risk of morality. The Japan Public Health Center-based Prospective Study recruited 42,736 men and 49,742 women free of chronic diseases and with an average of 57 years at baseline. Dietary acid load was calculated according to the NEAP and PRAL methods using data from food-frequency questionnaires. PRAL uses the estimated daily intakes of protein and phosphorus (both of which increase dietary acid load and PRAL score) and potassium, calcium, and magnesium (all of which decrease dietary acid load and PRAL score). NEAP uses the ratio of daily protein intake divided by the daily intake of potassium. After adjusting for many confounding factors (such as age, sex, smoking status) and compared to participants in the lowest quartile of dietary acid load, participants in the highest quartile had a significant 13 percent higher risk of dying during 17 years of follow-up. The risk increased of dying increased as PRAL scores increased from the first to the fourth quartile. Increased PRAL scores also predicted significant increased risks of death from cardiovascular disease and heart disease, but not from cancer or brain-related disease. The risks of all-cause and cardiovascular mortality increased sharply when PRAL scores rose above zero into the acidic realm but didn’t change much as PRAL scores became negative into the alkaline realm. Similar associations appeared using NEAP as the measure of dietary acid load.
Hypertension
Animal and human studies suggest a link between dietary acid load and blood pressure. Researchers at Harvard used data from 87,293 female participants with an average of 36 years in the Nurses’ Health Study II to see if diets with higher dietary acid load would predict greater risk of hypertension. Dietary data were collected every 4 years during 14 years of follow-up. Dietary acid load was calculated using a standard formula and using the ratio of animal protein to potassium intake and termed net endogenous acid production (NEAP). After adjusting for confounding factors and compared to participants in the highest quintile of NEAP, participants in the lowest quintile had a significant 14 percent lower risk of developing hypertension during follow-up. After further adjustment for intakes of protein and potassium, the risk was 23 percent lower. Similar results appeared using the ratio of animal protein to potassium intake as the measure of dietary acid load. Thus, reducing your dietary acid load could help reduce your risk of developing hypertension.
Impaired bone health
The dietary acid load in food may effect skeletal health. Researchers in the UK used cross-sectional data from 1,056 mostly pre-menopausal women with an average age of 47 years to determine if lower dietary acidity was linked to greater bone mass and less bone turnover. Bone mineral density was measured in the hip, spine, and forearm, while bone turnover was measured in the forearm. Dietary intake was evaluated using a food-frequency questionnaire. Dietary acidity was measured using the NEAP approach, which is based on the ratio of protein to potassium intake in the diet. After adjusting for confounding factors, lower values of energy-adjusted NEAP (less dietary acid load) significantly correlated with higher bone mass in the spine and forearm but not hip. Bone mass declined across quartiles in increasing NEAP values. Lower values of energy-adjusted NEAP were significantly correlated with higher forearm bone resorption (movement of calcium back into bone).
Type 2 diabetes
Researchers in the Netherlands and at Harvard used data from three large cohorts with long follow-ups – the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study – to investigate links between dietary acid load and risk of type 2 diabetes. A total of 187,486 women and men participants without diagnosed type 2 diabetes or cardiovascular disease at baseline comprised the study population. Dietary intake was evaluated with food frequency questionnaires administered every 4 years. Dietary acid load was calculated according to the NEAP and PRAL methods and with the ratio of animal protein to potassium. Dietary acid scores were grouped in quintiles from low to high. Diabetes was noted from self-reports and confirmed from medical records. After accounting for many confounding factors (including diabetes risk factors and diet quality) and compared to participants in the lowest quintile of dietary acid load, participants in the highest quintile had a significant 21, 19, and 26 percent higher risks of developing type 2 diabetes during follow-up per NEAP, PRAL, and the animal protein / potassium ratio methods after pooling data from the three cohorts. Interestingly, diabetes risk factors and diet quality did not fully explain the links between dietary acid load and type 2 diabetes. Other unknown factors must be involved.
Metabolic syndrome
Diets high in acid load may promote aspects of the metabolic syndrome, which reflects insulin resistance, obesity, blood fat abnormalities, and hypertension. Researchers in the Middle East conducted a meta-analysis of 8 cross-sectional studies that reported links between dietary acid load and prevalence of the metabolic syndrome. The NEAP and PRAL methods quantified dietary acid load. Patients with higher dietary acid load per NEAP or PRAL had a significant 42 and 76 percent higher odds, respectively, of having the metabolic syndrome. Each 10 mEq/day incremental increase in dietary acid load predicted a significant 2 and 28 percent higher odds of having the metabolic syndrome per NEAP and PRAL, respectively. Unfortunately, the studies reflected substantial publication bias (a shortage of studies that found no effect of dietary acid load on metabolic syndrome). Preliminary evidence suggests that diets lower in acid load might reduce the risk of the metabolic syndrome.
Kidney stones
Researchers at Harvard used cross-sectional data from three large cohorts (Nurses’ Health Study, Nurses’ Health Study II, Health Professionals Follow-up Study) to determine if dietary animal and vegetable protein and the ratio of animal to vegetable protein intake predicted the odds of having a kidney stone. Dietary intake was evaluated with food-frequency questionnaires. After adjusting for confounding factors and compared to the highest quintile of dairy protein intake, Nurses’ Health Study II participants in the lowest quintile had a significant 16 percent lower odds of having a kidney stone. For nondairy animal protein, the comparable odds were a significant 15 and 20 percent higher for participants in the Health Professionals Follow-up Study and the Nurses’ Health Study, respectively. Higher intakes of potassium was linked to lower odds of having a kidney stone for all three cohorts. Participants in all three cohorts with higher animal protein / potassium ratio had higher odds of a kidney stone, even after adjusting for total protein and potassium. The odds of a kidney stone may be related to the type of dietary protein (animal or plant). However, diets high in potassium or high in potassium compared to animal protein may reduce the odds of a kidney stone.
Amino acid review
Researchers in German and Uruguay reviewed chemistry of dietary acid load, foods that contribute to and reduce high dietary acid loads, and adverse effects of diets with high acid loads. Diets in developed countries typically lack sufficient potassium to offset the acid load arising from other items, especially meat, cheese, eggs, and processed foods. Animal-based protein contains three amino acids (lysine, arginine, histidine) that yield hydrochloric acid upon being metabolized. Similarly, animal-based protein contains three amino acids (methionine, homocysteine, cysteine) that yield sulfuric acid upon being metabolized. Plant-based contain lesser fractions of these acid-forming amino acids. Phosphorus-containing compounds also produce acidic metabolites. Animal products generally have more phosphorus per serving that fruits and vegetables, although lentils and pinto beans have relative high amounts of phosphorus. Fruits and vegetables contain relatively high levels of potassium and magnesium, which form alkaline metabolic products. Specifically, leafy green vegetables (beet greens, Swiss chard, spinach) top the chart for potassium and magnesium concentration per serving. Cross-sectional and cohort studies, and randomized controlled trials suggest that high dietary loads predict increased risks of cardiovascular disease, metabolic alterations, kidney disorders, and diabetes. Reducing dietary acid load primarily involves reducing intakes of meat, cheese, and eggs, while increasing intakes of fruits and vegetables.
Recent evidence that dietary acid load affects health
Researchers in Europe recently summarized the evidence that increased dietary acid load (which leads to chronic low-grade blood serum metabolic acidosis) predicts increased risks of chronic diseases. The list includes chronic kidney disease, hypertension, decreased bone quality, fatty liver disease, and cancer. Elevated blood serum acidity causes the kidneys to work harder to correct this imbalance, leading over time to increased risk of chronic kidney disease, which is typically progressive and incurable. However, dietary changes that reduce intakes of meat and protein and increase intakes of fruits and vegetables, especially green leafy vegetables, may help prevent chronic kidney disease and/or slow its progression. Higher dietary acid load also predicts increased risk of kidney stones. Hypertension is the leading cause of cardiovascular disease. Emphasizing fruits and vegetables and de-emphasizing meat and protein predicts lower blood pressure and lower risk of hypertension. Bone tissue serves as a source of calcium that can buffer against higher acid loads faster than the kidneys can. However, loss of calcium from bones may weaken them, placing older persons at greater risk of fractures. Observational studies suggest that higher dietary acid load predicts greater risk of certain cancers including breast, bladder, and lung. While the above seems disheartening, the simple shifting of dietary intake away from meat and protein to fruits and vegetables may reduce dietary acid load and limit risk of chronic diseases.
What to do
Evidence suggests that high dietary acid load predicts several serious, adverse health outcomes, although relatively little evidence comes from randomized controlled trials. That notwithstanding, the best way to avoid a high dietary acid load is to do something that you should probably be going anyway – ramping up your intake of fruits and vegetables (especially the leafy green kinds) and reducing your intake of meat, cheese, and eggs.
