Does an alkaline diet change your blood pH?

By about 0.014 units. That figure comes from a four-period study in which the same eight people ate diets built to be acid-forming and base-forming, matched for calcium, phosphate, sodium, protein and calories. Urine pH in the same study differed by 1.02 units. Urine pH is what the diet changes. Blood pH is what the cancer claim needs. The gap between those two numbers is the whole argument.

Does it protect your bones?

The first half of the idea holds up and the second does not. Making the diet more acid-forming reliably raises urine calcium, by about 66 mg a day per 47 mEq change. But across the five studies that met the strictest standard, there was no link between a change in urine acid and a change in the body's total calcium balance, in an analysis with a 94 percent chance of spotting a real effect. The calcium in the urine does not seem to be a net loss from the body.

What about the trial where potassium citrate increased bone density?

It is real, and it belongs in any honest account. 161 women past menopause with low bone mass got potassium citrate or potassium chloride for twelve months. The citrate group gained 1.87 percent bone density at the lower spine, 1.39 at the hip bone's neck and 1.98 at the total hip, all clear results. Both groups got potassium, so the comparison isolates the alkali. The catch is that a separate two-year study tested potassium citrate at two doses, next to 300 g a day of extra fruit and vegetables, and found no difference in bone density or bone turnover compared with a dummy pill.

There is no trial. A review screened 8,278 citations and read 252 summaries. One study met its criteria, no trials were found, and no studies of any kind were found on diet acid load or alkaline water as a cancer treatment. The one included study found no link between diet acid load and bladder cancer. That does not show the claim is false. It shows that after a thorough search there is almost nothing to judge.

Elimination4 studies in people cited

Alkaline diet

Q: Should I cut protein to lower my acid load?

The evidence that would justify that is the evidence that failed. The balance reviews found no sign that diet acid load pulls minerals from the skeleton. The cause-and-effect review found trials gave no evidence that phosphate, milk or grain foods harm bones. The medical review of this exact question raises the opposite worry: in older people, too little protein is a bigger problem for bone health than too much.

Written by Aaron CuhaReviewed Sep 2026

Also called: Acid-alkaline diet, Acid-ash diet, pH diet, Alkaline water

Half the idea holds up and half does not. Make the diet more acid-forming and the calcium in your urine rises, reliably. But the body's total calcium balance does not change, in an analysis with a 94 percent chance of spotting a real effect. And no study has found a way the diet would work at the body's normal pH.

What it actually is

Eat less of the foods classed as acid-forming, mainly meat, fish, hard cheese and grains, and more of the foods classed as alkaline-forming, mainly fruit and vegetables, often along with alkaline water or alkaline salts. The food classes themselves are real and measurable. A food's acid load on the kidneys is worked out from what it contains. It runs from an average top of around plus 23.6 mEq (a unit of acid) per 100 g for some hard cheeses, through 0 for fats and oils, to about minus 3 for fruit, fruit juice and vegetables. The predicted acid the body passes in urine lines up closely with urine pH, at a correlation of 0.83. So the food groups are not made up. What is disputed is what changing them does.

How its fans say it works

Two claims of very different strength, and they should be pulled apart before testing either. The acid-ash idea says the modern diet delivers a constant acid load. The body neutralises it by pulling alkaline minerals out of the skeleton, the freed calcium shows up in urine, and over decades this causes osteoporosis (thin, weak bones). That is a specific idea about the body with clear predictions, and it has been tested again and again in studies that measure every bit of calcium going in and out. The second, bigger claim is that an alkaline diet raises the body's pH and so prevents or treats cancer. That needs blood pH to move. But blood pH is held between roughly 7.35 and 7.45 by the lungs and kidneys, more or less whatever you eat. That is why urine pH and blood pH are different measurements, and why almost every study here reports the first.

What happened when calories were controlled

Best kind of study available: calories matched

Both groups ate the same number of calories, so a difference comes from what was in the diet, not how much people ate.

Calories are not the disputed factor here. Acid load is, and it has been controlled again and again in studies that measure every bit of calcium in and out, with calcium, phosphate, sodium, protein and calories matched between groups. The first half of the idea holds up: raise the acid load and urine calcium rises. The second half fails: the body's total calcium balance does not change.

Fenton 2011 weighed the case for cause and effect using a standard checklist (Hill's criteria), across 55 of 238 studies, including 22 trials and 11 studies that followed people over time. Urine calcium fitted the idea, but the calcium balance studies did not show the body losing calcium overall when acid load went up. No trial gave direct evidence of bones getting worse, meaning fractures from weak bones or bone strength measured by biopsy. The studies that followed people and did support the idea did not account for weight loss during follow-up, family history of osteoporosis, starting bone density or oestrogen levels. No study found a way the idea could work at the body's normal pH. And trials gave no evidence that phosphate, milk or grain foods play a harmful role in osteoporosis.
Fenton 2008 pooled 25 of 105 studies to measure the effect. On the comparison diets, the acid passed in urine averaged 47 mEq a day. A change of 47 mEq went with 1.6 mmol, or 66 mg, a day of extra calcium in acidic urine, and the link was clear and steady in both acidic and alkaline urine. The authors' own warning is the key sentence: this does not show that the calcium in urine comes from bone, or that it adds to osteoporosis.
A companion review attacked the idea through phosphate, which the acid-ash argument blames as a major acid source from dairy, meat and grains. It covered 12 studies, 30 study groups and 269 people. More phosphate lowered urine calcium and increased the calcium the body kept, at both high and low calcium intakes, whatever form of phosphate supplement was used. Every analysis ran against the idea.
Fenton 2009 tested exactly that question, using only studies that met the US Institute of Medicine's strict standards for measuring calcium balance. Five of 16 studies qualified. As acid in urine went up, urine calcium clearly went up too. But there was no link between a change in urine acid and a change in the body's total calcium balance. That analysis had a 94 percent chance of spotting a real effect, so finding nothing is a much stronger statement than usual. There was also no link with N-telopeptides, a marker of bone breakdown.
Buclin 2001 is the study that backs the idea, and it belongs here in full. Eight healthy volunteers each ate acid-forming and base-forming diets, in four periods, with calcium, phosphate, sodium, protein and calories matched. Blood pH differed by an average of only 0.014, a clear but tiny difference. Urine pH differed by 1.02, also clear. That is the cleanest example of how different these two measurements are in scale. Urine calcium was 74 percent higher on the acid-forming diet, and C-telopeptide, a marker of bone breakdown, was 19 percent higher, both clear results. The authors read that as the extra calcium coming from bone. Eight people, with four days of diet preparation.

What happened when people just ate it

The fair real-world test is the trials that gave alkaline salts, because alkaline salts are exactly what the diet tries to deliver through food. Here the research truly disagrees with itself. Macdonald 2008 put 276 women aged 55 to 65, past menopause, into four groups for two years: potassium citrate at 55.5 mEq a day, potassium citrate at 18.5 mEq a day, a dummy pill, or 300 g a day of extra fruit and vegetables, which supplies about 18.5 mEq of alkali. There was no difference between groups in three markers of bone breakdown and building. One breakdown marker (deoxypyridinoline) was lower in the high-dose group at four to six weeks, and that did not last. Spine bone loss was 1.8 percent on the dummy pill against 2.1 percent across the other groups, no real difference. The authors concluded that providing alkali does not explain any long-term benefit of fruit and vegetables on bone. Jehle 2006 goes the other way, and it is a good study. 161 women past menopause with low bone density (a T score between minus 1 and minus 4) got 30 mEq a day of potassium citrate or 30 mEq a day of potassium chloride for twelve months, and neither they nor the researchers knew who got which. Bone density rose more in the citrate group: by 1.87 percent at the lower spine, 1.39 percent at the hip bone's neck and 1.98 percent at the total hip, all clear results. Urine calcium stayed lower, rising urine citrate showed the body was staying more alkaline, and bone breakdown markers fell. The wrist and total body showed no real change. Because both groups got potassium, the comparison isolates the citrate part, which makes it the cleanest test of the alkali claim, and it is positive. Squaring the two is not hard, and it is worth doing plainly. A potassium salt given at a drug-sized dose to women with low bone mass is a different thing from eating fruit instead of cheese. The study that tested the food version next to the salt version found both did nothing. On the cancer claim there is almost nothing to square. A review screened 8,278 citations and read 252 summaries. One study met its criteria, no trials were found, and no studies at all were found on diet acid load or alkaline water for treating cancer. The one included study, which followed people over time, found no link between diet acid load and bladder cancer (an odds ratio of 1.15, too close to call), and 1.72 among long-term smokers, also too close to call.

Protein, and whether it muddies the result

Protein is the food group this idea blames, and this is where the failed test matters most in practice. The calcium balance reviews found no evidence that raising the diet's acid load pulls minerals from the skeleton. The cause-and-effect review found trials gave no evidence that phosphate, milk or grain foods harm bones in osteoporosis. The medical review of this exact question points the other way: in older people, too little protein is a bigger problem for bone health than too much. So anyone cutting protein to lower their acid load is acting on the half of the idea that did not survive testing, and may be working against the part of the protein research that matters most to them. The measured protein intakes and what each did are in the protein section of this site, and the view on older adults is on the high protein page.

The measured intakes behind the protein figures are on the protein page.

What reliably moves

Measure	Direction	From
Urine pH	Changes reliably and by a lot	1.02 units between matched acid-forming and base-forming diets. A food's calculated acid load lines up closely with urine pH, at a correlation of 0.83, so the food groups predict this marker well.
Blood pH	Barely	An average difference of 0.014 units between matched diets built to be acid-forming and base-forming. That is a clear but tiny difference, too small to matter to the body. This is the number that decides what the cancer claim can and cannot rest on.
Urine calcium	Down on an alkaline diet, reliably	74 percent lower on the base-forming diet in the matched study, and about 66 mg a day per 47 mEq change in urine acid in the pooled review. Found again and again, and misread again and again as bone loss.
The body's total calcium balance	Unchanged	No link between a change in urine acid and a change in calcium balance, across the five studies that met the strictest standard, in an analysis with a 94 percent chance of spotting a real effect. The extra calcium in urine is not a net loss from the body.
Bone breakdown markers	Disputed	N-telopeptides showed no link with urine acid in the balance review. C-telopeptide ran 19 percent higher on the acid-forming diet in the eight-person study. Deoxypyridinoline fell with potassium citrate in one trial and not in another. The marker research does not agree with itself.
Bone density	No change on food, better in one potassium citrate trial	No difference at two years in a four-group trial of 276 women that included a fruit and vegetable group. Up 1.87 percent at the lower spine at twelve months in 161 women on potassium citrate, against potassium chloride.
Fractures	Never measured	No trial has given direct evidence of bones getting worse, meaning a fracture from weak bones or bone strength by biopsy. The outcome the whole idea is about has never been measured in any trial of it.
Cancer cases or response to treatment	One study, no link, and nothing else	After screening 8,278 citations, one bladder cancer study that followed people, with an odds ratio of 1.15, too close to call. No trials found, and no studies at all of an alkaline diet or alkaline water as cancer treatment.

Long term, and serious health events

Two years is the longest trial, and it found nothing for food. No trial of this diet has counted fractures, and none has measured a cancer outcome. The most useful long-term statement is the list of what the cause-and-effect review found missing. There was no trial evidence of bones getting worse. The long-term studies that followed people did not account for weight loss during follow-up, family history, starting bone density or oestrogen levels. In the lab, 19 cell studies found no way the idea could work at the body's normal pH. One point is worth adding without dressing it up as a finding. The foods this diet pushes people toward are fruit and vegetables, and the foods it pushes them away from include processed meat and hard cheese. So the diet as people follow it is unlikely to do harm, even though the reason given for it did not hold up. That is not the same as the idea being right, and the two are constantly mixed up in the material that sells it.

Sources

Review of studies2011
Causal assessment of dietary acid load and bone disease: a systematic review & meta-analysis applying Hill's epidemiologic criteria for causality
Nutrition Journal
A review kept 55 of 238 studies: 22 that changed people's diets, 11 that followed people over time, and 19 in a dish. Acid in the diet raised calcium in urine but did not change the body's overall calcium balance. No study showed faster bone loss, and none found how it could work at the body's normal pH. The studies that followed people did not account for weight loss, family history, starting bone density or estrogen.
55 of 238 studies, including 22 randomised interventions, 11 prospective cohorts and 19 cell studies. Urine calcium was consistent with the hypothesis and calcium balance was not. No intervention study provided direct evidence of osteoporosis progression, no study revealed a mechanism at physiological pH, and cohorts were uncontrolled for weight loss, family history, baseline bone density and oestrogen status.
Review of studies2009
Meta-analysis of the effect of the acid-ash hypothesis of osteoporosis on calcium balance
Journal of Bone and Mineral Research
A review found five of 16 studies strong enough to judge calcium balance. More acid in urine went with more calcium in urine. But it did not change how much calcium the body kept, or a marker of bone breakdown. Calcium in urine does not show what is happening to the body's calcium overall.
Five of 16 studies met the strictest methodological standards for calcium balance. Significant linear relationship between rising net acid excretion and urine calcium (p < 0.0001); no relationship with change in calcium balance (p = 0.38 at 94 percent power) and none with N-telopeptides (p = 0.95). Changes in urine calcium do not accurately represent calcium balance.
Review of studies2009
Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis
Nutrition Journal
A review pooled 12 studies with 269 people. More phosphate in the diet lowered calcium in urine and helped the body keep more calcium, whether calcium intake was high or low. Every result went against the idea that acid forming foods drain calcium from bone.
12 studies, 30 intervention arms, 269 subjects. Higher phosphate intakes decreased urine calcium excretion and increased calcium retention at both high and low calcium intake and regardless of protonation. Every finding ran contrary to the acid-ash hypothesis.
Review of studies2008
Meta-analysis of the quantity of calcium excretion associated with the net acid excretion of the modern diet under the acid-ash diet hypothesis
American Journal of Clinical Nutrition
A review kept 25 of 105 studies. On normal diets the body got rid of about 47 units of acid a day. A change that size went with about 66 mg more calcium a day in urine. The authors say this does not prove the calcium came from bone.
25 of 105 studies. Net acid excretion on control diets averaged 47 mEq/day, and a 47 mEq change was associated with 1.6 mmol/day (66 mg/day) of urine calcium in acidic urine, with a significant linear relation in acidic and alkaline urine. The authors state this is not evidence that the excreted calcium came from bone.
Study in people2001
Diet acids and alkalis influence calcium retention in bone
Osteoporosis International
Eight volunteers ate an acid forming diet and a base forming diet in turn. Calcium, phosphate, salt, protein and calories were all matched. Blood acidity barely changed, while urine acidity changed a lot. On the acid forming diet, calcium in urine was 74 percent higher and a marker of bone breakdown was 19 percent higher. This is the study that backs the idea, and it had only eight people.
Eight volunteers, four-period double crossover, acid-forming against base-forming diets matched for calcium, phosphate, sodium, protein and calories. Blood pH differed by 0.014 (p = 0.002) and urine pH by 1.02 (p < 0.0001). Urine calcium 74 percent higher and C-telopeptide 19 percent higher on the acid-forming diet. The trial that supports the mechanism, at n = 8.
Study in people2008
Effect of potassium citrate supplementation or increased fruit and vegetable intake on bone metabolism in healthy postmenopausal women: a randomized controlled trial
American Journal of Clinical Nutrition
276 women past menopause were followed for two years in four groups. One ate 300 g a day of extra fruit and vegetables, and others took potassium citrate. Markers of bone turnover did not differ between groups. Spine bone loss was 1.8 percent on a dummy pill and 2.1 percent on treatment, about the same. The authors say alkali does not explain any long term bone benefit of fruit and vegetables.
276 postmenopausal women, two years, four arms including 300 g/day extra fruit and vegetables. No between-group difference in bone turnover markers. Spine bone density loss 1.8 percent on placebo against 2.1 percent on treatment (p = 0.88). Authors conclude alkali provision does not explain any long-term benefit of fruit and vegetables on bone.
Study in people2006
Partial neutralization of the acidogenic Western diet with potassium citrate increases bone mass in postmenopausal women with osteopenia
Journal of the American Society of Nephrology
The study that found a benefit. 161 women past menopause with thin bones took potassium citrate or potassium chloride for twelve months. The citrate group gained more bone density: 1.87 percent more at the spine, 1.39 percent at the hip bone neck and 1.98 percent at the whole hip. Both groups got potassium, so the difference came from the citrate.
The positive trial. 161 postmenopausal women with T score minus 1 to minus 4, randomised double blind to 30 mEq potassium citrate or 30 mEq potassium chloride for twelve months. Intergroup bone density increase 1.87 percent at L2 to L4, 1.39 percent at femoral neck and 1.98 percent at total hip, all p < 0.001. Both arms received potassium, isolating the citrate anion.
Review of studies2016
Systematic review of the association between dietary acid load, alkaline water and cancer
BMJ Open
A review screened 8,278 papers on diet acid, alkaline water and cancer, and only one study qualified. There were no trials, and no studies at all on using diet acid or alkaline water to treat cancer. The one study found no link with bladder cancer. The authors say promoting these for cancer is not justified.
8,278 citations screened, 252 abstracts reviewed, one study met inclusion. No randomised trials located and no studies at all of dietary acid or alkaline water for cancer treatment. The one included cohort found no association with bladder cancer (OR 1.15, 0.86 to 1.55, p = 0.36). Promotion for cancer prevention or treatment described as not justified.
Review of studies2012
The alkaline diet: is there evidence that an alkaline pH diet benefits health?
Journal of Environmental and Public Health
The review alkaline diet fans cite most. It searched studies on pH, acid load, bone, muscle, growth hormone, back pain, vitamin D and chemotherapy, and also looked at popular books. Its own conclusion is only that there may be some value and more studies are needed.
The most-cited affirmative review, included here because it is what advocates cite. A narrative PubMed search across pH, potential renal acid load, bone, muscle, growth hormone, back pain, vitamin D and chemotherapy, which also evaluated lay books. Its own conclusion is that there may be some value and that further studies are warranted.
Study in people1995
Potential renal acid load of foods and its influence on urine pH
Journal of the American Dietetic Association
This is the scoring system every study here uses. It rates how much acid a food leaves for the kidneys to clear. Some hard cheeses score as high as 23.6 per 100 g, fats and oils score 0, and fruits, juices and vegetables score about minus 3. The predicted acid matched urine acidity closely.
The classification underlying every study in this block. Calculated potential renal acid load ranges from an average maximum of 23.6 mEq per 100 g for some hard cheeses through 0 for fats and oils to about minus 3 for fruits, juices and vegetables, and predicted net acid excretion correlates with urine pH at r = 0.83 (p < 0.001).
Review of studies2013
Does a high dietary acid content cause bone loss, and can bone loss be prevented with an alkaline diet?
Journal of Clinical Densitometry
A review for doctors. Acid in the diet or high protein may raise calcium in urine, but the evidence that this causes thin bones is mixed. Studies of more alkaline diets, or of potassium citrate or bicarbonate pills, have not reliably helped bone. In older people, too little protein is a bigger problem for bones than too much.
Clinical review. Acid loading or a high protein intake may raise urine calcium, and the evidence supporting a role in the development of osteoporosis is not consistent. Intervention studies with a more alkaline diet or with potassium citrate or bicarbonate have not consistently shown a bone benefit. States that in the elderly, inadequate protein intake is a greater problem for bone health than protein excess.

What people report

These are things people say about their own eating. Nobody checked them, so they are not evidence. They are here because they tell you what to expect and what to watch for, which the studies do not. They cannot tell you whether anything works.

More energy and less bloating in the first weeks. This is reported consistently, and it fits just as well with simply eating more fruit and vegetables and less processed food.
Urine pH strips turning the expected colour within a day or two. That is the one effect the body's chemistry clearly predicts, and it is often read as proof of a whole-body change it does not show.
No change in any blood test on retest, reported often by people who checked. That is the expected result, given what the four-period study measured.
Less joint pain, reported often in the community and never measured in any study of this diet.
Difficulty and expense, especially around alkaline water systems, the most common reason people stop.
Anxiety about acidity, described by some who left the diet as the part that outlasted it.
Protein intake dropping without meaning to, reported by people who cut meat, fish, eggs and dairy because of the acid score. That is exactly the problem the bone research warns about in older adults.

Sources: Alkaline diet communities, wellness publishing, and the alkaline water industry, which makes money from the claim. Note that the most-cited supportive review in the medical literature looked at popular books alongside published studies, and concluded only that there may be some value and that more studies are needed. Unchecked self-report throughout.

Who this is wrong for

Anyone using it instead of treatment for a diagnosed cancer. A review screened 8,278 citations and found no trial of an alkaline diet or alkaline water for treating cancer of any kind, and no trial of either for preventing cancer.
Anyone with kidney disease or adrenal insufficiency, or on a potassium-sparing water pill, an ACE inhibitor or an angiotensin receptor blocker (common blood pressure drugs). The alkali trials gave 18.5 to 55.5 mEq a day of potassium salts under medical supervision, and potassium load is a question for a prescriber, not a forum.
Anyone cutting protein to lower their acid load, older adults in particular. The medical review of this exact question concludes that in older people too little protein is a bigger problem for bone health than too much, and the balance studies found no evidence that diet acid load pulls minerals from the skeleton.
Anyone expecting their blood pH to change. The measured difference between matched diets built to be acid-forming and base-forming was 0.014 units, against a urine pH difference of 1.02.
Anyone paying extra for alkaline water because of the cancer claim, or being sold urine pH test strips as a measure of the whole body's acid balance.
Anyone with a history of eating disorders. A diet that sorts every food onto a good or bad side of a calculated score is a poor fit.

Questions

Does an alkaline diet change your blood pH?: By about 0.014 units. That figure comes from a four-period study in which the same eight people ate diets built to be acid-forming and base-forming, matched for calcium, phosphate, sodium, protein and calories. Urine pH in the same study differed by 1.02 units. Urine pH is what the diet changes. Blood pH is what the cancer claim needs. The gap between those two numbers is the whole argument.
Does it protect your bones?: The first half of the idea holds up and the second does not. Making the diet more acid-forming reliably raises urine calcium, by about 66 mg a day per 47 mEq change. But across the five studies that met the strictest standard, there was no link between a change in urine acid and a change in the body's total calcium balance, in an analysis with a 94 percent chance of spotting a real effect. The calcium in the urine does not seem to be a net loss from the body.
What about the trial where potassium citrate increased bone density?: It is real, and it belongs in any honest account. 161 women past menopause with low bone mass got potassium citrate or potassium chloride for twelve months. The citrate group gained 1.87 percent bone density at the lower spine, 1.39 at the hip bone's neck and 1.98 at the total hip, all clear results. Both groups got potassium, so the comparison isolates the alkali. The catch is that a separate two-year study tested potassium citrate at two doses, next to 300 g a day of extra fruit and vegetables, and found no difference in bone density or bone turnover compared with a dummy pill.
Can it treat cancer?: There is no trial. A review screened 8,278 citations and read 252 summaries. One study met its criteria, no trials were found, and no studies of any kind were found on diet acid load or alkaline water as a cancer treatment. The one included study found no link between diet acid load and bladder cancer. That does not show the claim is false. It shows that after a thorough search there is almost nothing to judge.
Should I cut protein to lower my acid load?: The evidence that would justify that is the evidence that failed. The balance reviews found no sign that diet acid load pulls minerals from the skeleton. The cause-and-effect review found trials gave no evidence that phosphate, milk or grain foods harm bones. The medical review of this exact question raises the opposite worry: in older people, too little protein is a bigger problem for bone health than too much.