Does a High Dietary Acid Content Cause Bone Loss, and Can Bone Loss Be Prevented With an Alkaline Diet?

Abstract

A popular concept in nutrition and lay literature is that of the role of a diet high in acid or protein in the pathogenesis of osteoporosis. A diet rich in fruit and vegetable intake is thought to enhance bone health as the result of its greater potassium and lower "acidic" content than a diet rich in animal protein and sodium. Consequently, there have been a number of studies of diet manipulation to enhance potassium and "alkaline" content of the diet to improve bone density or other parameters of bone health. Although acid loading or an acidic diet featuring a high protein intake may be associated with an increase in calciuria, the evidence supporting a role of these variables in the development of osteoporosis is not consistent. Similarly, intervention studies with a more alkaline diet or use of supplements of potassium citrate or bicarbonate have not consistently shown a bone health benefit. In the elderly, inadequate protein intake is a greater problem for bone health than protein excess.

Full text

Special Section on Bone and Nutrition
Does a High Dietary Acid Content Cause Bone Loss, and
Can Bone Loss Be Prevented With an Alkaline Diet?
David A. Hanley*
,1
and Susan J. Whiting
2
1
Division of Endocrinology and Metabolism, Departments of Medicine, Community Health Sciences and Oncology,
University of Calgary, Calgary, AB, Canada; and
2
College of Pharmacy and Nutrition, University of Saskatchewan,
Saskatoon, SK, Canada
Abstract
A popular concept in nutrition and lay literature is that of the role of a diet high in acid or protein in the path-
ogenesis of osteoporosis. A diet rich in fruit and vegetable intake is thought to enhance bone health as the result of
its greater potassium and lower ‘‘acidic’’ content than a diet rich in animal protein and sodium. Consequently, there
have been a number of studies of diet manipulation to enhance potassium and ‘‘alkaline’’ content of the diet to im-
prove bone density or other parameters of bone health. Although acid loading or an acidic diet featuring a high
protein intake may be associated with an increase in calciuria, the evidence supporting a role of these variables
in the development of osteoporosis is not consistent. Similarly, intervention studies with a more alkaline diet or
use of supplements of potassium citrate or bicarbonate have not consistently shown a bone health benefit. In the
elderly, inadequate protein intake is a greater problem for bone health than protein excess.
Key Words: Acid-ash hypothesis; acid-base balance; alkaline potassium; fruits and vegetables.
Introduction
In this work we examine evidence that a change in acid-
base balance through dietary means can affect bone health.
This concept is sometimes termed the ‘‘acid-ash hypothesis’’
and is often promoted as an important factor in the develop-
ment of osteoporosis. This hypothesis suggests that foods
high in ‘‘acidic’’ content (e.g., animal protein and grains)
cause a chronic acidemia because of their sulfate and phos-
phate content, whereas fruits and vegetables create a more
alkaline environment because of their greater potassium-
organic anion content and may even prevent age-related
bone loss and osteoporosis. It proposes that the acidic anions
provide an increased acid load on the kidney and that the in-
creased net acid excretion (NAE) is accompanied by in-
creased calcium loss in the urine. Furthermore, proponents
of the acid-ash hypothesis suggest that, to maintain a normal
acid-base homeostasis, there is an increase in bone resorption
to buffer the excess dietary ‘‘acid.’’
Further credence was given to this concept when the Dietary
Reference Intake recommendation for potassium in 2005 by
the Institute of Medicine (1) made a specific reference to in-
creasing alkaline sources of potassium, that is, fruits and veg-
etables, to enhance bone health. However, recommendations
that restrict protein intake to reduce NAE, and restriction of
otherwise-healthy foods because of their ‘‘acidity.’’ may also
have implications that could be detrimental to bone health. A
recent review of the impact of acid-base balance on bone sug-
gests the proponents of the acid-ash hypothesis of osteoporosis
have underestimated the ability of the kidney and respiratory
system to deal with dietary sources of acid (2). The purpose
of this work is to examine the different types of evidence for
an acid-base effect on bone and to provide recommendations
for dietary intakes that are in-line with the evidence.
AcideBase Effects on Bone:
Observational Studies
A role for dietary vegetables and fruit on bone health has
emerged in the literature. Population-based studies have
Accepted 06/01/13.
*Address correspondence to: David A. Hanley, MD, FRCPC,
Richmond Road Diagnostic and Treatment Centre, 1820 Richmond
Road S.W., Calgary, AB T2T5C7 Canada. E-mail: dahanley@
ucalgary.ca
420
Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health, vol. 16, no. 4, 420e425, 2013
ÓCopyright 2013 by The International Society for Clinical Densitometry
1094-6950/16:420e425/$36.00
http://dx.doi.org/10.1016/j.jocd.2013.08.014

reported that increased potassium intake through vegetables
and fruits is associated with increased bone mineral density.
For example, in 1999 Tucker et al, by using cross-sectional
and prospective Framingham data of subjects 69e97 yr,
showed that potassium and magnesium intakes, as well as fruit
and vegetable intake, were significantly associated with greater
bone mineral density (BMD) and with a slower rate of bone
loss, albeit the latter only in men (3). Fruit and vegetable intake
has been associated with a lower NAE, and thus, some authors
have related these studies to the concept of alkaline diets being
beneficial to bone.
Observational studies on protein, however, have not been
consistent in linking a protein-induced change in NAE to
changes in bone measures or fracture risk. Prospective as well
as intervention studies on the effect of protein intake and
BMD and/or fracture rates have almost all shown that elderly
women benefitted from an increase in protein intake (2).
Indeed, the most recent European osteoporosis guidelines
recommend a daily protein intakeof 1 g/kg body weight, a value
greater than the current dietary recommendations in the
United States and Canada (4). Thus, attempts to change NAE
by reducing protein intake may be detrimental to skeletal health.
The Dietary Approaches to Stop Hypertension (DASH)
diet, which emphasizes the intake of vegetables, fruits, and
low-fat dairy products and the avoidance of processed foods
(Table 1), may have bone benefits. In a 3-month trial among
186 middle-aged men and women, investigators reported that
the DASH diet significantly reduced biochemical markers of
bone turnover (5). However, the DASH diet does not neces-
sarily provide evidence for an acid-base effect because it
also incorporates many important healthful changes, includ-
ing sufficient calcium and protein intakes (O1000 mg and
O75 g, respectively); and a sodium intake below the upper
level of 2300 mg, which may reduce sodium-induced hyper-
calciuria.
A large study has corroborated the bone-health effect of in-
creasing fruits and vegetables. In the Women’s Health Initia-
tive Dietary Modification study, a low-fat and increased fruit,
vegetable, and grain educational intervention in close to
50,000 postmenopausal women was evaluated with respect
to incident hip, other site-specific, and total fractures and
self-reported falls, and, in a subset, BMD (6). After an 8-
year follow-up, the intervention group had a lower rate of
reporting 2 or more falls than did the comparison group. Al-
though few trials have been conducted in humans, many ani-
mal and cell studies indicate that a diet high in fruit supplies
carotenes, polyphenols, and other active plant compounds that
may play beneficial roles in bone metabolism (7).
The Alkaline Potassium Hypothesis
Advocates of the Alkaline Potassium Diet Hypothesis use
the Paleolithic diet as being ‘‘ideal’’ for preserving bone in-
tegrity (8). The Paleolithic diet of hunteregatherers is high
in potassium and bicarbonate precursors from vegetables
and fruit, which advocates believe counteracted the very
high protein intakes of those early humans. Herein dietary
potassium at levels of 400 mEq per day (close to 3 times
the current adequate intake for potassium) would be essential
to maintain bone integrity. In contrast, the modern western
diet is low in alkaline equivalents, and cereals, although
they are plant-based, do not provide the alkalizing effect of
fruits and vegetables. In addition, the modern western diet
is high in sodium, mainly because of processed foods. To re-
turn to a more favorable ratio of potassium (K)-to-sodium
(Na) in the diet, that is, to a ratio that is comparable with
what humans ate in preagricultural diets, both an increase
in potassium and an avoidance or severe restriction of sodium
chloride is necessary (8). Interestingly, Canadian and Ameri-
can food guide revisions have reduced the amount of cereal
grains servings and increased the amounts of fruit and vege-
table servings, that is, Eating Well with Canada’s Food Guide
(released in 2007) and MyPyramid (released in 2005). Both of
these food guides resemble the DASH diet. As illustrated in
Table 1, the DASH diet (and food guides that resemble it)
is probably the ‘‘best’’ dietary pattern that can be achieved to-
day, via the use of largely unprocessed foods available in the
marketplace. By following the DASH diet, one can attain a di-
etary Na:K ratio of approximately 1:1. This ratio is a marked
improvement over dietary intakes that typically occur, that is,
w2:1, in the United States and Canada.
The Acid-Ash Hypothesis
The Acid-Ash Hypothesis is a variant of the Alkaline Potas-
sium Hypothesis. Both are premised on the argument that
acidic compounds in the diet (high protein, high phosphate,
or other ‘‘acidic’’ anions like sulfate) have an adverse effect
on bone, whereas alkaline components, such as fruit and veg-
etables, will counter this effect. Early work centered on mea-
suring NAE after consumption of diets varying in protein,
with or without variations in alkaline salts or alkaline foods
(2). However, it has never been demonstrated that, in healthy
subjects, manipulation of the diet caused any disturbance in
blood pH or bicarbonates. The ‘‘metabolic acidosis’’ predicted
with the Acid-Ash Hypothesis has remained hypothetical.
Systematic Reviews of Acid-Base and Bone
A moderately large amount of literature exists on the influ-
ence of dietary acid or alkali on bone. Although the common
theme is that a diet high in protein or phosphate would be det-
rimental to the skeleton, recent systematic reviews of this lit-
erature have not supported these premises.
The proponents of the Acid-Ash Hypothesis have sug-
gested that a diet providing high phosphate content would
be acidic and that this would result in negative calcium bal-
ance and bone loss. However, a recent meta-analysis of stud-
ies of dietary intervention with phosphate supplements found
no support for this concept (9). This analysis examined stud-
ies of phosphate supplementation that also controlled cal-
cium intake by the subjects. Control of sodium intake was
not consistent in the studies reviewed, and only one of the
studies used randomization and provided the Institute of
High Dietary Acid Content and Bone Loss 421
Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health Volume 16, 2013

Medicine’s recommendations for calcium balance studies.
However, despite the variability in the quality of the studies,
regression analysis indicated that as phosphate intake in-
creased, urinary calcium decreased, irrespective of the vari-
ability in dietary calcium intake in these studies, or
whether the phosphate supplement was alkaline, neutral or
acidic. In fact, the reduction in urinary calcium excretion
was greatest with the use of acidic phosphate supplements.
However, the calcium balance was more positive with the
neutral or alkaline phosphate supplements. Very few studies
examined the effect of phosphate supplement on bone turn-
over markers or bone density; therefore, no consistent effect
could be ascertained.
This meta-analysis of the phosphate supplementation liter-
ature actually provides modest support for the opposite con-
clusion from what would be expected from the Acid-Ash
Hypothesis; that is, a high phosphate intake is associated
with increased calcium retention and a reduction in calciuria
(9). Nevertheless, the quality of the studies reviewed was not
high, and calcium balance is only a weak surrogate for long-
term effects on bone mass or bone quality.
Fenton et al also have provided 2 further meta-analyses of
literature testing the acid content of the diet on calcium bal-
ance and other bone-related outcomes (10,11). The initial
meta-analysis examined the effect of NAE on calciuria in
healthy individuals (10). In all, 25 dietary intervention studies
(of 105 reviewed) met appropriate inclusion criteria for the
meta-analysis; of note, only 2 were randomized, controlled
trials. There was a strong association between NAE and cal-
cium excretion, although 5 of the studies did not show a rela-
tionship. It was estimated that the contribution of a typical
‘‘western’’ diet to NAE was 47 mEq per day, which corre-
sponded to an increase in calcium excretion of 1.6 mmol
per day. They calculated that, if diet could cause a person
to lose this much extra calcium in the urine each day, and
if the source of this calcium was bone, during an extended pe-
riod of time a clinically significant skeletal loss could occur.
However, the authors cautioned that the studies do not
Table 1
Intakes of Nutrients Important for Bone Health According to Serving Sizes of Foods of the DASH Diet
Food groups (examples
of a serving)
DASH diet
(minimum
servings/day)
Approximate
calcium intake
(foods fortified),
mg
Approximate
sodium
intake, mg
Approximate
potassium
intake, mg
Approximate
protein
intake, g
Milk products
Milk, 1% (250 mL, 1 cup) 2 575 720 520 17
Cheese (50 g)
Grain products
Bread (1 slice) 7 160 950 560 21
Cereal (30 g, 1 cup)
Rice (1 cup)
Vegetable group (raw leafy vegetable)
Lettuce (1 cup) 4 200 100 970 6
Spinach (1 cup)
Fruit group
Banana (medium size) 4 95 10 1610 4
Orange (medium size)
Orange juice (1/2 cup)
Meat
Lean meat (80 g) 2 or less 50 135 550 19
Fish (80 g)
Poultry (80 g)
Alternatives
Egg (1) 0.6 (4 servings/week
from nuts, seeds,
and dry beans)
30 35 180 8
Cooked dry beans (125 g)
Tofu (100 g)
Peanut butter (2 tbsp-30 mL)
Total e1110 1950
a
4390 75
Note: Calcium, potassium, and protein are close to, or exceed, current recommendations, whereas sodium intake falls below its upper level.
Modified from Institute of Medicine (1).
Abbr: DASH, Dietary Approaches to Stop Hypertension.
a
Consuming unsalted products reduces sodium intake further.
422 Hanley and Whiting
Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health Volume 16, 2013

provide evidence that the source of the increase in calciuria is
bone, and there are obvious adaptive measures in the hor-
monal regulation of calcium absorption and metabolism that
could allow adaptation to an increase in urinary calcium.
These authors then went on to a meta-analysis of the liter-
ature examining the effect of interventions (diet or supple-
ments) that manipulated dietary acid/base on calcium
balance (11). The studies had to meet the following criteria:
healthy adult subjects; report change in NAE in relation to
calcium balance; randomize subjects to the order of treat-
ments; and the investigators had to follow the standard recom-
mendations for calcium balance studies (7 d of tested diet
before outcome measurement; all consumed foods were
provided to the subjects; accurate assessment of amounts con-
sumed; and laboratory analysis to confirm the calcium content
of the food). Only 5 studies met these criteria, and although
a positive relationship was seen between NAE and calcium
excretion, as in the earlier meta-analysis of 25 studies, there
was no significant relationship between NAE and calcium
balance (R2 50.003; p50.38). Therefore, the authors
concluded that changes in urinary calcium excretion do not
accurately reflect calcium balance and that the promotion of
an alkaline diet to reduce NAE in the interests of preserving
the skeleton is not justified by available evidence. Finally, the
authors of a systematic review and meta-analysis of the effect
of dietary acid on bone disease (osteoporosis), applying Hill’s
criteria of causality, reviewed 238 studies, of which 55 met
criteria for inclusion (12). The authors found the available ev-
idence does not support a causal association between dietary
acid load and osteoporosis and that there was not enough ev-
idence to support recommendation of an alkaline diet for bone
health.
Recent Randomized Controlled Trials
To support the Alkaline Potassium Hypothesis, a number of
randomized controlled trials have been published. Only those
of 2 years’ duration that included direct measures of bone
density are examined here. There have been 3 such studies in
adult women who were given alkaline potassium as either
the citrate or bicarbonate salt alone with calcium and vitamin
D; 2 studies published bone data together in one report (13)
provided null evidence for an effect, whereas a third study
(14) provides support for the Alkaline Potassium Hypothesis.
Macdonald et al (15) completed a trial of potassium citrate
(in doses of 18.5 and 55 mEq/d) or fruit and vegetable con-
sumption (predicting 18.5 mEq/d potassium intake) in post-
menopausal women for 2 years. At the same time, Frassetto
et al (13) were testing potassium bicarbonate (in doses of
30, 60, and 90 mEq/d), also in women and for 2 years. These
authors presented the results of both studies in a single paper
wherein they presented all BMD results related to salt load;
only those with moderate salt load are plotted in Fig. 1. Over-
all, no change in bone density could be attributed to potas-
sium citrate, potassium bicarbonate, or fruit and vegetable
consumption. The authors grouped their data to determine
whether sodium intake was a factor in the lack of an effect
of alkaline potassium, and this factor proved to be of no sig-
nificance.
In contrast, in a recent randomized controlled trial involv-
ing women 65e80 yr, investigators found a bone benefit of
60 mEq/d potassium citrate (14). As shown in Fig. 2, BMD
in the potassium group was 1%e2% greater than placebo;
similar results were obtained using when bone microarchitec-
ture was assessed with peripheral quantitative computed to-
mography. Biochemical markers of bone turnover indicated
less bone resorption at 6 months whereas the formation
marker was greater at 24 months of intervention. Why one
study should show clear results whereas the others could
not is not apparent. The ingestion of 60 mEq/d by the women
in the study by Jehle et al (14) study brought their mean po-
tassium intakes above the recommended level of 120 mEq/d,
Fig. 1. Mean change in BMD with 24 months treatment
with alkaline-potassium (dose as mEq/d) or as fruits and veg-
etables (F&V) in women 41e105 yr, in situation of medium
mean arterial pressure, combining data from 2 studies, n 525
or 65, depending on study. Frassetto et al (8). BMD, bone
mineral density.
Fig. 2. Mean change in BMD with 24 months’ treatment
with alkaline-potassium (dose as mEq/day), in women
65e80 yr, n 584e85 per group. Jehle et al (14). BMD,
bone mineral density.
High Dietary Acid Content and Bone Loss 423
Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health Volume 16, 2013

but their sodium intakes (as measured by the use of urinary
excretion levels) remained increased at approximately 160
mEq (compared with a recommended level of 56 mEq) (1).
There is no obvious explanation why one study shows
a bone benefit of potassium and the other two do not. Jehle
et al (14) propose a link between the significant decrease in
NAE with potassium citrate and the increment in bone density
and structural parameters, but one has to question whether
a change in blood pH of 0.02 within the normal range is of
clinical significance for bone. It is possible there may be other
effects of potassium citrate independent of NAE and acid base
status. A larger and longer-term clinical trial is needed.
Conclusion
In this paper, attention has been given to the concept that
an alkaline diet or alkaline potassium salts promote calcium
retention. As demonstrated in the systematic reviews and
meta-analyses, there is not enough evidence to support
a causal relationship between the acid/alkali composition of
a diet and bone health. However, some studies do support
a bone benefit of a ‘‘healthy’’ diet with increased vegetable
and fruit content or supplements containing potassium bicar-
bonate or citrate: (1) epidemiologic studies in which fruit and
vegetable intake was demonstrated to be positive for BMD or
other markers of bone health; and (2) experimental studies
either in laboratory animals or human volunteers showing
that alkaline potassium salts promoted a more positive cal-
cium balance, or reduced markers of bone resorption, in com-
parison to alkaline sodium salts or to acid-forming potassium
salts. The data, however, are not clear-cut, as some clinical
trials have shown that greater potassium intake does not pro-
tect against bone loss. Also, the question has arisen as to
whether the alkaline salt must have potassium as the cation,
although sodium clearly would not benefit bone health be-
cause of other mechanisms. Thus current recommended in-
take (AI) for potassium, of 4700 mg (120 mEq) for ages
14 years and over is based, in part, on the alkaline-
potassium hypothesis. Meeting this high level of potassium
necessitates choosing a healthy diet emphasizing fruits and
vegetables with a lowered sodium intake and adequate cal-
cium, such as the DASH diet, Canada’s Food Guide, and My-
Pyramid. This dietary choice, and not intake of an alkaline
potassium salt, is more likely to help optimize bone health.
References
1. Institute of Medicine. 2005 Dietary reference intakes: sodium,
chloride, potassium and sulphate. Washington, DC: National
Academy Press.
2. Bonjour JP. 2013 Nutritional disturbance in acidebase balance
and osteoporosis: a hypothesis that disregards the essential ho-
meostatic role of the kidney. Br J Nutr 4:1e10.
3. Tucker KL, Chen H, Hannan MT, et al. 1999 Potassium, magne-
sium, and fruit and vegetable intakes are associated with greater
bone mineral density in elderly men and women. Am J Clin Nutr
69:727e736.
4. Kanis JA, McCloskey EV, Johansson H, et al. on behalf of the Sci-
entific Advisory Board of the European Society for Clinical and
Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO)
and the Committee of Scientific Advisors of the International Os-
teoporosis Foundation (IOF). 2013 European guidance for the di-
agnosis and management of osteoporosis in postmenopausal
women. Osteoporos Int 24(1):23e57.
5. Lin PH, Ginty F, Appel LJ, et al. 2003 The DASH diet and so-
dium reduction improve markers of bone turnover and calcium
metabolism in adults. J Nutr 133:3130e3136.
6. McTiernan A, Wactawski-Wende J, Wu LL, et al. 2009 Low-fat,
increased fruit, vegetable, and grain dietary pattern, fractures,
and bone mineral density: the Women’s Health Initiative Dietary
Modification Trial. Am J Clin Nutr 89:1864e1876.
7. Shen C-L, von Bergen V, Chyua M-C, et al. 2012 Fruits and
dietary phytochemicals in bone protection. Nutr Res 32:
897e910.
8. Frassetto LA, Hardcastle AC, Sebastian A, et al. 2012 No evi-
dence that the skeletal non-response to potassium alkali supple-
ments in healthy postmenopausal women depends on blood
pressure or sodium chloride. J Nutr 138:419Se422S.
9. Fenton TR, Lyon AW, Eliasziw M, et al. 2009 Phosphate de-
creases urine calcium and increases calcium balance: a meta-
analysis of the osteoporosis acid-ash diet hypothesis. Nutr J 8:41.
10. Fenton TR, Eliasziw M, Lyon AW, et al. 2008 Meta-analysis of
the quantity of calcium excretion associated with the net acid ex-
cretion of the modern diet under the acid-ash diet hypothesis.
Am J Clin Nutr 88:1159e1166.
11. Fenton TR, Eliasziw M, Lyon AW, et al. 2009 Meta-analysis of
the effect of the acid-ash hypothesis of osteoporosis on calcium
balance. J Bone Miner Res 24:1835e1840.
Key Points
A diet high in protein, providing a high phos-
phate and sulfate content, has been thought
to increase the acid load on the kidney. This in-
creased net acid excretion has been associated
with increased urinary calcium loss. Meta-anal-
yses of studies of dietary acid/base intake and
bone do not support a major influence.
Urinary calcium loss does not necessarily
mean a negative calcium balance or bone
loss. Further, a high phosphate intake is more
consistently associated with lower calcium ex-
cretion and increased calcium retention.
Evidence for alkalinizing the diet with in-
creased intake of fruits and vegetables may
be beneficial for bone, but more studies are
needed, in the form of well-conducted clinical
trials of long duration. There is contradictory
evidence of bone effects of intervention with
potassium citrate or bicarbonate supplements
from randomized clinical trials.
Nevertheless, there are compelling reasons to
promote a diet high in fruit and vegetables
for bone health. Intakes for bone health based
on dietary recommendations found in govern-
ment food guides or dietary patterns recom-
mended for chronic disease such as the
DASH diet, should be encouraged.
424 Hanley and Whiting
Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health Volume 16, 2013

12. Fenton TR, Tough SC, Lyon AW, et al. 2011 Causal assessment
of dietary acid load and bone disease: a systematic review and
meta-analysis applying Hill’s epidemiologic criteria for causal-
ity. Nutr J 10:41.
13. Frassetto LA, Hardcastle AC, Sebastian A, et al. 2012 No evi-
dence that the skeletal non-response to potassium alkali supple-
ments in healthy postmenopausal women depends on blood
pressure or sodium chloride intake. Eur J Clin Nutr 66:
1315e1322.
14. Jehle J, Hulter HN, Krapf R. 2013 Effect of potassium citrate on
bone density, mincroarchitecture, and fracture risk in healthy
older adults without osteoporosis: a randomized controlled trial.
J Clin Endocrinol Metab 98:207e217.
15. Macdonald HM, Black AJ, Aucott L, et al. 2008 Effect of po-
tassium citrate supplementation or increased fruit and vegeta-
ble intake on bone metabolism in healthy postmenopausal
women: a randomized controlled trial. Am J Clin Nutr 88:
465e474.
High Dietary Acid Content and Bone Loss 425
Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health Volume 16, 2013