Alkaline Diet

The acid-ash food classification

The sorting of foods into acid and alkaline groups traces to early twentieth-century laboratory chemistry. A systematic review of bone outcomes reports that Sherman published tables in 1912 listing the acid and base contributions of 64 foods, based on the mineral content of the ash left when each food was burned. A British Columbia dietitian fact sheet describes the same method: the ash was mixed with water, its pH was measured, and foods were labeled acid-ash or alkaline-ash.

Remer and Manz revised the approach in 1995 with a calculation called potential renal acid load, or PRAL, which estimates a food's effect on the acid the kidneys must excrete from nutrient content. In their study the calculated net acid excretion correlated with urine pH (r = 0.83), which they proposed could guide dietetic work such as preventing recurrent kidney stones. The sources reviewed do not describe PRAL as a test of body or blood acidity.

The bone hypothesis

A review of the nutritional acid load hypothesis of osteoporosis traces it to investigations in people with chronic kidney disease in the 1960s, in which bone mineral was interpreted as a buffer against accumulating acid. The reviewer argues that this interpretation was later questioned on theoretical and experimental grounds, and that data from kidney disease were then extrapolated to healthy people and turned into dietary recommendations.

Popular books, supplements and water products

Reviewers describe the modern alkaline diet as a consumer movement built on the older acid-ash hypothesis. A 2016 systematic review says the hypothesis was developed more than 100 years ago and lists a 2002 book, The pH Miracle by Robert Young, among the promotional sources. It describes marketing through websites, books and videos, plus supplements and water 'alkalinizer' machines.

An earlier review reports that alkaline diets and products have been marketed through flyers, magazines, direct mail and books, and that marketers encourage people to measure urine or saliva pH. The sources reviewed do not trace the movement's history in more detail than this.

Names in use

Clinical and research sources use several names for the same idea. A dietitian fact sheet calls it the acid-ash diet, a 2012 review title calls it the alkaline pH diet, and bone researchers speak of the acid-ash hypothesis or of dietary acid load. Promotional material usually says simply the alkaline diet, and may extend the label to alkaline water and alkalizing supplements.

Technical terms

Net acid excretion is the amount of acid the kidneys excrete in urine, and potential renal acid load is a calculated estimate of the acid a food adds to that load. These are measures of what passes through the kidneys. They differ from the pH of a food as eaten: the fact sheet notes that a food's own pH does not predict the pH of its ash, so a sour-tasting item can still be classed alkaline-ash.

Acid-base language in clinical medicine is narrower. The British Dietetic Association states that blood pH changes only in metabolic acidosis, which it associates with critically ill people, and that there is no consensus on which foods are acidic or alkaline. One review proposes a milder, low-grade diet-related acidosis, a concept that is debated.

How promoters describe the pattern

Promoters describe a way of eating that favors foods labeled alkaline-forming and avoids those labeled acid-forming, with the aim of making the body less acidic. A cancer-center fact sheet notes that, in practice, this pattern limits many high-protein choices, including meat and dairy products. Details differ between books and websites, and this page does not reproduce any program.

Testing and related products

Followers are often encouraged to test urine or saliva acidity and adjust their eating to match, and to buy supplements or water alkalizers. The sources reviewed describe these as consumer practices promoted by websites, books and salespeople, and none describes a standardized clinical protocol.

Related Machipedia pages

This page belongs to the Dietary Approaches family on Machipedia. Readers comparing eating patterns may also consult the pages on Plant-Based Diet and Raw Food Diet, and the page on Master Cleanse for a short-term program. The sources reviewed for this page do not describe how alkaline diet books relate to those patterns, or to Naturopathy, so no link is asserted here.

Claims about cancer

Promoters claim that modern diets acidify the body and cause cancer, and that an alkaline diet can treat cancer after diagnosis. A British Columbia fact sheet summarizes the premise as cancer thriving in an acidic environment but not surviving in an alkaline one, and the British Dietetic Association describes the claim as creating a hostile environment for cancer.

Claims about bone, ageing and other conditions

The acid-ash hypothesis of osteoporosis holds that a diet high in protein and grain foods and low in potassium produces an acid load, increases urine calcium and draws calcium out of the skeleton. Promoters have also linked acidity to cardiovascular disease, diabetes and high blood pressure.

One narrative review argues that a diet-driven mild acid load builds with age as kidney regulation declines, and discusses possible effects on muscle, growth hormone and back pain. The author presents these as areas needing further research, and the review is not systematic.

Blood pH and urine pH

A dietitian fact sheet states that blood pH is held between 7.35 and 7.45 by the bicarbonate buffering system and the kidneys, so urine pH can range from about 4.5 to 8.5 while blood pH stays stable. It says a diet of mostly acid-ash foods has not been shown to move blood pH outside the normal range. The British Dietetic Association states that dietary intake does not alter blood pH.

A systematic review reports that in one randomized trial diet changes moved systemic pH by 0.014 units and urine pH by 1.02 units. Diet therefore changes urine pH, which the sources describe as a normal kidney function.

Bone health

A 2011 systematic review and meta-analysis screened 238 studies and included 55, including 22 randomized interventions. Urine calcium rose with acid load, but calcium balance studies did not show loss of whole-body calcium, and no study showed a mechanism at physiological pH. It concluded that no evidence showed an alkaline diet protects bone.

A 2009 meta-analysis of five randomized studies of adults found no relationship between changes in net acid excretion and calcium balance or a bone turnover marker. A Canadian cohort of 795 adults followed for fractures found that urine pH and acid excretion did not predict fractures or bone density change, though the authors noted that a single fasting urine sample may limit that result.

Findings are not uniformly null. A 2025 meta-analysis of six observational studies reported a marginal association between dietary acid load and fracture (pooled odds ratio 1.10, 95% confidence interval 0.99 to 1.21). A trial in 201 healthy older adults found that potassium citrate supplements, given with calcium and vitamin D, raised lumbar spine bone density over 24 months compared with placebo. That trial tested a supplement, not an alkaline diet.

Cancer

A 2016 systematic review of dietary acid load, alkaline water and cancer screened 8,278 citations and 252 abstracts and included one study. No randomized trials and no studies of treatment were located. The included cohort study, in Finnish male smokers, found no association between estimated diet acid load and bladder cancer. The authors concluded there is almost no research to support or disprove the claims, and that promoting the diet for cancer prevention or treatment is not justified.

Another review found no studies showing a direct link between diet-induced acidosis and cancer, and proposed possible cell-signaling pathways as a hypothesis. Dietitian sources add that solid tumors acidify their own surroundings through their metabolism, a result of the cancer rather than a cause, which does not change blood pH.

Differing interpretations

A 2012 narrative review states that no scientific literature supports an alkaline diet for cancer prevention and that dietary acid load does not equal osteoporosis, yet suggests an alkaline-style diet rich in fruits and vegetables may be prudent. A bone review argues the hypothesis disregards renal acid-base homeostasis.

Delayed care and restrictive eating

A systematic review reports that salespeople reportedly approach patients with cancer and promote water alkalinizers as a treatment. Any approach used in place of established treatment can delay care, and this page does not suggest replacing or postponing medical care. The British Dietetic Association advises telling the oncology team or a dietitian about any diet being followed, and warns that restrictive diets allowing few foods are unlikely to be balanced.

A British Columbia dietitian fact sheet states that following an alkaline diet may not be suitable for people with cancer, because limiting many high-protein foods without replacing them can leave protein needs unmet and lead to muscle loss. It also advises that people at risk of malnutrition may find acid-labeled foods difficult to include.

Kidney disease and potassium

The fact sheet notes that the body's ability to regulate blood pH is impaired in kidney disease and in some respiratory conditions. A literature review states that a potassium-rich diet is not recommended for people with advanced chronic kidney disease or end-stage kidney disease because of the risk of life-threatening hyperkalemia, although the same review finds weak evidence for intense dietary potassium restriction and calls for individualized advice.

Alkaline-style eating and alkali supplements can increase potassium and other mineral intake, so people with kidney disease or on related medication would need individual advice from their care team. The sources reviewed do not report a systematic assessment of the harms of alkaline salts or supplements.

Urine test strips and alkaline water

The authors of the Canadian fracture cohort argued that urine pH testing to identify people at risk of osteoporosis should be discouraged, since urine pH did not predict fractures. The dietitian fact sheet says testing can mislead people into believing they are acidic or alkaline and can motivate continued diet change and testing, and that alkaline water changes urine pH but not whole-body or blood pH.

Training and professional oversight

The sources reviewed describe no training standard, credential or professional register specific to the alkaline diet, and none was found. Evidence-based guidance on the topic comes from dietetic professional groups such as the British Dietetic Association's oncology specialist group and registered dietitians at a Canadian cancer agency. See Dietetics for how that profession is organized.