Examining the relationship between diet-induced acidosis and cancer.
ABSTRACT Increased cancer risk is associated with select dietary factors. Dietary lifestyles can alter systemic acid-base balance over time. Acidogenic diets, which are typically high in animal protein and salt and low in fruits and vegetables, can lead to a sub-clinical or low grade state of metabolic acidosis. The relationship between diet and cancer risk prompts questions about the role of acidosis in the initiation and progression of cancer. Cancer is triggered by genetic and epigenetic perturbations in the normal cell, but it has become clear that microenvironmental and systemic factors exert modifying effects on cancer cell development. While there are no studies showing a direct link between diet-induced acidosis and cancer, acid-base disequilibrium has been shown to modulate molecular activity including adrenal glucocorticoid, insulin growth factor (IGF-1), and adipocyte cytokine signaling, dysregulated cellular metabolism, and osteoclast activation, which may serve as intermediary or downstream effectors of carcinogenesis or tumor promotion. In short, diet-induced acidosis may influence molecular activities at the cellular level that promote carcinogenesis or tumor progression. This review defines the relationship between dietary lifestyle and acid-base balance and discusses the potential consequences of diet-induced acidosis and cancer occurrence or progression.
- SourceAvailable from: Felice N Jacka[Show abstract] [Hide abstract]
ABSTRACT: In 21st-century public health, rapid urbanization and mental health disorders are a growing global concern. The relationship between diet, brain function and the risk of mental disorders has been the subject of intense research in recent years. In this review, we examine some of the potential socioeconomic and environmental challenges detracting from the traditional dietary patterns that might otherwise support positive mental health. In the context of urban expansion, climate change, cultural and technological changes and the global industrialization and ultraprocessing of food, findings related to nutrition and mental health are connected to some of the most pressing issues of our time. The research is also of relevance to matters of biophysiological anthropology. We explore some aspects of a potential evolutionary mismatch between our ancestral past (Paleolithic, Neolithic) and the contemporary nutritional environment. Changes related to dietary acid load, advanced glycation end products and microbiota (via dietary choices and cooking practices) may be of relevance to depression, anxiety and other mental disorders. In particular, the results of emerging studies demonstrate the importance of prenatal and early childhood dietary practices within the developmental origins of health and disease concept. There is still much work to be done before these population studies and their mirrored advances in bench research can provide translation to clinical medicine and public health policy. However, the clear message is that in the midst of a looming global epidemic, we ignore nutrition at our peril.Journal of PHYSIOLOGICAL ANTHROPOLOGY 07/2014; 33(1):22. · 1.16 Impact Factor
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ABSTRACT: The extracellular pH (pHe) of many solid tumors is acidic as a result of glycolytic metabolism and poor perfusion. Acidity promotes invasion and enhances metastatic potential. Tumor acidity can be buffered by systemic administration of an alkaline agent such as sodium bicarbonate. Tumor-bearing mice maintained on sodium bicarbonate drinking water exhibit fewer metastases and survive longer than untreated controls. We predict this effect is due to inhibition of tumor invasion. Reducing tumor invasion should result in fewer circulating tumor cells (CTCs). We report that bicarbonate-treated MDA-MB-231 tumor-bearing mice exhibited significantly lower numbers of CTCs than untreated mice (P < 0.01). Tumor pHe buffering may reduce optimal conditions for enzymes involved in tumor invasion such as cathepsins and matrix metalloproteases (MMPs). To address this, we tested the effect of transient alkalinization on cathepsin and MMP activity using enzyme activatable fluorescence agents in mice bearing MDA-MB-231 mammary xenografts. Transient alkalinization significantly reduced the fluorescent signal of protease-specific activatable agents in vivo (P ≤ 0.003). Alkalinization, however, did not affect expression of carbonic anhydrase IX (CAIX). The findings suggest a possible mechanism in a live model system for breast cancer where systemic alkalinization slows the rate of invasion.BioMed research international. 01/2013; 2013:485196.
Examining the relationship between diet-induced
acidosis and cancer
Ian Forrest Robey*
Increased cancer risk is associated with select dietary factors. Dietary lifestyles can alter systemic acid-base balance
over time. Acidogenic diets, which are typically high in animal protein and salt and low in fruits and vegetables,
can lead to a sub-clinical or low-grade state of metabolic acidosis. The relationship between diet and cancer risk
prompts questions about the role of acidosis in the initiation and progression of cancer. Cancer is triggered by
genetic and epigenetic perturbations in the normal cell, but it has become clear that microenvironmental and
systemic factors exert modifying effects on cancer cell development. While there are no studies showing a direct
link between diet-induced acidosis and cancer, acid-base disequilibrium has been shown to modulate molecular
activity including adrenal glucocorticoid, insulin growth factor (IGF-1), and adipocyte cytokine signaling,
dysregulated cellular metabolism, and osteoclast activation, which may serve as intermediary or downstream
effectors of carcinogenesis or tumor promotion. In short, diet-induced acidosis may influence molecular activities at
the cellular level that promote carcinogenesis or tumor progression. This review defines the relationship between
dietary lifestyle and acid-base balance and discusses the potential consequences of diet-induced acidosis and
cancer occurrence or progression.
Keywords: Acid-base balance, Diet, Acidosis, Cancer
Diet, cancer, and ‘acidity’
The relationship between diet and cancer is well known
[1-3]. Dietary intake exists as the largest external or en-
vironmental epigenetic factor capable of driving the de-
velopment or maintenance of cancer. The American
Institute for Cancer Research (AICR) comprehensive
global report has compiled numerous studies demon-
strating associations between dietary habits and cancer
risk . The findings recommend increased or regular
consumption of vegetables, fruits, whole grains, and
legumes, while discouraging excess consumption of sug-
ary and energy-dense foods and drinks, red and pro-
cessed meats, and salty processed foods (www.aicr.org).
Acidity is a well known factor associated with cancer.
Lower pH levels in the extracellular space promote the
invasive and metastatic potential of cancer cells [5-14].
Extracellular acidity is mostly generated by tumor cells
due to upregulated proton [H+] and lactic acid produc-
tion . This phenomenon is distinct from ‘acidity’
caused by a net-acid diet. A net-acid diet or acidogenic
diet is determined by the balance between acid and
base-forming dietary constituents. Most fruits and vege-
tables are net-base producing foods since the metabo-
lized products are organic anion precursors such as
citrate, succinate, and conjugate bases of carboxylic acids
[16-18]. The final metabolite of these precursors is bicar-
bonate anion. Sulfur containing amino acids, methionine
and cysteine, typically found in meats, eggs and dairy
products, are oxidized into sulfuric acid which is ultim-
ately net-acid producing . Cationic amino acids such
as lysine and arginine can be acid producing if their an-
ionic counterpart is chloride, sulfate, or phosphate.
However, if the anionic component is a metabolizable
organic acid (glutamate or aspartate), there is almost no
impact on systemic acidity [17,18]. Other dietary factors are
known to influence acid-base status as well. Sodium chlor-
ide is reported to be an independent and causal factor for
inducing metabolic acidosis in a dose-dependent manner
[19,20]. Conversely, potassium salts, and to a lesser degree
magnesium, serve as a countervailing effect on net acid
excretion and help to promote alkaline balance [21,22].
Arizona Respiratory Center, University of Arizona, 1501 N. Campbell Ave.,
Suite 2349, PO Box 245030, Tucson, Arizona 85724, USA
© 2012 Robey; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Robey Nutrition & Metabolism 2012, 9:72
Acidogenic dietary intake such as high protein con-
sumption can have an immediate effect on increasing
net acid production while low protein lacto-vegetarian
consumption can result in significantly reduced net acid
excretion [23,24]. Short-term dietetic acid loading may
cause temporary acid-base disequilibrium, but is quickly
compensated and has no measureable clinical effect. A
persistent acidogenic diet, however, raises the likelihood
of an increased [H+] surplus and chronically lower levels
of serum bicarbonate if compensatory processes become
less efficient and are unresolved by dietary adjustments.
Potential long-term effects of acidogenic diets are fur-
ther compounded by the reduction of renal function typ-
ically from ageing [16,25-28].
Blood pH from prolonged or chronic acidogenic diets
is reported to be near the lower physiological range
(7.36-7.38) rather than the higher end (7.42-7.44). Spe-
cifically, persistent acidogenic diets have the potential to
cause small decreases in blood pH and plasma bicarbon-
ate, but not beyond the normal physiological range. This
condition is described as ‘diet-induced’, ‘low-grade’, or
‘chronic metabolic acidosis’ [28-30] or sometimes ‘latent
acidosis’ . Diet-induced acidosis is distinct from clin-
ical metabolic acidosis in that clinical metabolic acidosis
occurs when factors other than just acidogenic diet con-
tribute a system’s inability to compensate for blood [H+]
perturbations, typically resulting in blood pH below 7.35
. The patho-physiological effects of clinical metabolic
acidosis are well known , while the true pathophysio-
logical impact of long-term, diet-induced acidosis is not
well understood. For example, it is unknown if [H+] ac-
cumulation from chronic diet-induced acidosis can be
stored at the cellular level if it does not play a role in
lowering blood pH or is compensated by competent
renal or respiratory function. Studies of the impact of
clinical metabolic acidosis on biological systems may still
be informative towards understanding the effects of diet-
induced acidosis because they examine how acid-base
disequilibrium causes physiological stress and influences
molecular pathways active in disease processes .
It is generally understood that the cancer condition
evolves from genetic and epigenetic changes in the normal
cell. Both microenvironmental and systemic factors exert
selective pressures that aid in the initiation or aggravation
of tumors. Acid-base disequilibrium is considered a type
of systemic stress. With the understanding that long-term
acidogenic diets potentially exert chronic physiological
stress, the question proposed here is: Can diet-induced
acidosis increase cancer risk or promote existing tumors?
Cortisol and acid-base balance
Acid-base balance in the body influences adrenal hor-
mone production of cortisol. When bicarbonate [HCO3
levels are low the kidneys upregulate glutaminase activity
and trigger cortisol production [35-37]. Studies in animals
and humans have reported that system cortisol levels are
enhanced by acid-base disruption through transiently
induced metabolic acidosis . Acidosis appears to medi-
ate cortisol activity through the pituitary-adrenal cortex-
renal glutaminase I axis . Dietary induction of acidosis
increases serum cortisol concentrations . In healthy
adult humans serum and salivary cortisol is increased sig-
nificantly within hours after a high protein meal, and cor-
tisol levels were dependent on the protein content of the
The converse to these findings is shown in a study
designed to neutralize the acidogenic effect of the
‘Western’ diet, characterized by a high consumption of
meat, salt, sugar and fat, and proportionately lower intake
of fruit, vegetables, and whole grains. The relationship to
cortisol levels and acid-base status were examined in
six healthy men and three women measuring serum
and urine cortisol concentrations along with cortisol
metabolite levels (tetrahydrocortisone and tetrahydrocor-
tisol) in the urine of individuals with sodium and potas-
sium chloride replaced with equimolar amounts of
sodium and potassium bicarbonate in an otherwise
similar diet under “metabolic ward conditions”. Within
24 hours, urinary and plasma cortisol and correspond-
ing metabolites were significantly lower, signaling lower
cortisol production and activity. Urinary pH and serum
Not all studies report a positive correlation between
high protein, potentially acidogenic diets, and cortisol
levels. These studies did not assess acid-base balance in
their experimental populations so it is difficult to con-
firm if these studies are directly comparable to findings
linking acidogenic dietary intake and increased cortisol
production. It is likely that factors such as gender and
body mass index are relevant inconsistencies between
various reports [42-44].
Many of these studies suggest there may be a role for
diet-induced acidosis in modulating systemic cortisol
levels, and that neutralization of acid loading through
alkalinization may reduce cortisol levels. Moreover, most
of the studies evaluating the role of acidogenic intake on
cortisol demonstrate that the interventions had an acute
and dose-dependent effect on cortisol levels, suggesting
a direct or closely linked dynamic between acid-base sta-
tus and system cortisol levels. Finally, the studies show
that diet-induced acidosis is mild and subsequent induc-
tion of cortisol activity, although higher in serum con-
centration, is sub-clinical and within the normal serum
range . If there were pathophysiological conse-
quences it could only be derived from chronic or persist-
ent conditions maintained on an acidogenic diet.
-] levels increased while serum pH remained
Robey Nutrition & Metabolism 2012, 9:72
Page 2 of 11
Cortisol bioactivity in cancer
There is no clear mechanism linking cortisol bioactivity
directly with carcinogenesis, but studies have reported
that cortisol signaling may exert biological influence on
existing tumors. Androgen-independent prostate tumors
expressing high levels of androgen receptor can be
stimulated by cortisol and its metabolite cortisone,
resulting in growth promotion and proliferation. The
mechanism for this interaction is made possible due to a
mutation in the androgen receptor that favors ‘promis-
cuous’ binding of additional signaling molecules like
glucocorticoids . In some breast cancer studies glu-
cocorticoids suppress growth by blocking cell cycle pro-
gression . Tumor inhibition appears to be androgen
dependent at least in some cell lines [47,48]. In colon
cancer, cortisol signaling inhibits 11β-hydroxysteroid de-
hydrogenase 2 (11βHSD2) enzymatic activity which pre-
vents activation of the COX-2 tumor promoter, an early
activation marker for colon carcinogenesis. The diversity
of tumor responses to glucocorticoid signaling suggests
that the relationship between hormonal activity and
tumor regulation is receiver-dependent. The following
sub-sections discuss the possible indirect role of cortisol
signaling in cancer risk and carcinogenesis.
Cortisol and tryptophan metabolism
Cortisol activates the tryptophan metabolism pathway
which is carried out by rate-limiting enzymes of trypto-
phan catabolism, 2,3-dioxygenase (TDO) and indolea-
mine 2,3-dioxygenase (IDO). Cortisol directly stimulates
TDO activation and may augment IDO activity indir-
ectly through inflammatory cytokine signaling such as
interferon gamma [49,50]. Excessive or chronic cortisol
production acquired from a ‘Western’ dietary lifestyle
could play a role in augmenting the tryptophan metabol-
ism pathway and drive downstream molecular events
that promote carcinogenesis.
The product of TDO and IDO activity, kynurenine, has
several roles in promoting tumorigenesis. Kynurenine
inhibits the activation of effector T-cells when tryptophan
levels are low. Incapacitating effector T-cell function is
suggested as an important component in increasing vul-
nerability to tumor development [51-53]. Tryptophan me-
tabolism also promotes immune tolerance of professional
antigen presenting cells (APCs) which are critical in acti-
vating other immune cells [51,53,54]. Finally, kynurenine
binds to aryl hydrocarbon receptor (AHR), which med-
iates TDO and IDO signaling in regulatory T-cells. The
activated AHR suppresses the stimulation of regulatory
T-cells involved in inhibiting early tumor development
[51,55-57]. The connection between diet-induced, low-
grade hypercorticoidism and the effect on tryptophan me-
tabolism to subsequently promote tumor development
has not been adequately explored. Furthermore, it is
unknown what other factors may enhance, regulate, or at-
tenuate these signaling events, but a persistent reduction
of effective immune surveillance capability promoted in-
directly by diet-induced acidosis could cultivate microen-
vironmental conditions favorable for oncogenic cells to
develop metastatic potential.
Cortisol and insulin resistance
Upregulated cortisol bioactivity driven by diet-induced
acidosis may be a factor in metabolic syndrome by pro-
moting insulin resistance. Chronic hyperglucocorticoid-
ism upregulates visceral obesity while reducing insulin
sensitivity mainly in visceral adipocytes which appear to
be more responsive to cortisol than subcutaneous adipo-
cytes due to higher expression levels of glucocorticoid
receptors [58,59]. Visceral adipocytes also exhibit greater
11βHSD1 activity, which converts cortisone to bioactive
cortisol . Glucocorticoids stimulate visceral adipo-
cytes to increase the activity of lipoprotein lipases, while
simultaneously suppressing insulin mediated glucose up-
take [61-66]. This phenomenon suggests that cortisol
activated adipocytes are less efficient in storing fatty
acids which tend to increase the level of free fatty acids
in circulation and contributes to diminished insulin sen-
Glucocorticoid signaling promotes insulin resistance
through other signaling pathways as well. Insulin stimu-
lated glucose transporter-4 (GLUT-4) translocation to the
cell surface of adipose tissue is suppressed by glucocorti-
coids. Cortisol directly inhibits insulin secretion from pan-
creatic beta cells. Finally, cortisol can reduce insulin
mediated vasodilation of endothelial cells, and suppresses
peripheral insulin driven glucose uptake [68-70].
Acidosis associated insulin resistance through cortisol
activity may result in compensatory pancreatic insulin
secretion and higher levels of circulating insulin in the
serum, a condition known as hyperinsulinemia. Epidemi-
ology studies have shown a positive correlation between
circulating insulin levels and increased risk and patho-
genesis of colorectal and pancreatic cancers [71-76], can-
cers of the endometrium , kidney cancer  and
breast cancer [79,80]. Longitudinal studies report a
higher risk for breast cancer in women with hyperinsuli-
nemia [81-83]. Human studies are confirmed by experi-
mental data showing that injected insulin promotes
tumorigenesis in animal models for colon  and
breast [85,86] cancer. Insulin deficiency or insulin block-
ing reduces tumor incidence or progression and is re-
versible with re-introduction of insulin . Several of
the study findings conclude that hyperinsulinemia is an
independent risk factor from obesity and diabetes .
Insulin is a pleiotropic hormone with both mitogenic
and metabolic properties. It binds with the highest affin-
ity to its own receptor and with lower affinity to the
Robey Nutrition & Metabolism 2012, 9:72
Page 3 of 11
insulin growth factor-1 (IGF-1) receptor. The insulin re-
ceptor exists in two isoforms, IR-A and IR-B. IR-A is
expressed at lower levels than IR-B, but has greater
mitogenic activity when stimulated by insulin. Addition-
ally, both insulin receptor isoforms can form heterodi-
meric complexes with the IGF-1 receptor. The IR-A/IGF
hybrid receptor is expressed in all human tissues and
binds to insulin with high affinity . Activation of
these receptors by insulin stimulates cellular transform-
ation and promotes malignancy. Insulin promotes cellu-
lar proliferation, migration, and cellular survival mainly
through the MAPK pathway and sometimes through
PI3K pathway . It is proposed that chronically
exposed cells to even moderately elevated insulin levels
may favor cell proliferation and subsequently increase
the risk for malignant transformation . Thus, persist-
ent diet-induced acidosis favorable for maintaining
chronically high levels of cortisol could be supportive of
insulin sensitized tumor development.
Insulin growth factor
Studies examining the relationship between diet-induced
acidosis and insulin growth factor (IGF-1) levels have
varied outcomes. Acute induction of systemic acidosis
appears to reduce serum IGF-1 levels. Short-term (5-7
days) induction of metabolic acidosis in healthy male
subjects using ammonium chloride (NH4Cl) causes a
significant reduction in serum IGF-1 levels , con-
firming the results of an animal study carried out under
similar parameters . An adult fasting between 5-10
days induces a mild metabolic acidosis and appears to
have the effect of reducing plasma IGF-1 concentrations
as well [92-94]. Plasma IGF-1 levels are doubled by
treatment with bicarbonate in individuals with renal
tubular acidosis . In healthy subjects though,
neutralization of diet-induced acidosis with bicarbonate
treatment for a 7 day period does not have a significant
impact on IGF-1 levels .
High protein consumption over long-term periods
(months to years), which promotes greater net acid pro-
duction and subsequent latent or low-grade metabolic
acidosis, appears to have the opposite outcome from
short term studies on IGF-1 levels. Studies conducted
for 12 weeks or longer revealed a strong correlation be-
tween increased dietary protein and higher serum IGF-1
levels, suggesting at least long-term dietary habits, not
short-term perturbations, significantly impact IGF-1
serum concentrations [96-99]. Another epidemiological
study in healthy middle-aged and elderly male partici-
pants concluded that while protein consumption was
positively correlated to serum IGF-1 levels, the finding
was only consistent in individuals with a body mass
index (BMI) of <25kg/m2. There was no significant rela-
tionship between protein consumption and IGF-1 levels
in obese individuals (BMI >25kg/m2). The study also
reported that even while protein consumption increased
IGF-1 serum levels, there was an age dependent decline
in IGF-1 levels overall . The findings suggest a po-
tential for chronic acidogenic or ‘Western’ diets to ele-
vate IGF-1, but other factors complicate this dynamic
and require additional study. While it is reasonable to
predict that the individuals in these long-term studies
have developed low-grade acidosis from their diet, it
does not mean that acidosis is a driver of IGF-1 upregu-
lation. Furthermore, if diet-induced acidity upregulates
IGF-1, as suggested from the long-term dietary studies,
it is not yet determined if this occurs directly or indir-
ectly through cortisol signaling [2,88,89].
IGF-1 binding to the insulin receptor has been shown to
inhibit apoptosis and increase target cell proliferation,
thus linking its signaling activity to the risk of different
forms of cancer [101-103]. Several case control studies
have demonstrated a possible link between IGF-1 bio-
[104,105], colorectal [106-108], and breast . The
serum IGF-1concentrations in the case population of
the studies were relatively consistent with the ranges
measured in the previously discussed studies evaluating
the effects of ‘Western’ diet consumption on IGF-1
levels [97,100]. IGF-1 median levels of about 200ng/ml
in individuals younger than 70 years of age were typic-
ally associated with high protein diets (~90-105 g/day).
Leptin is an adipocyte derived hormone cytokine that
plays a role in regulating body weight and energy bal-
ance in the hypothalamus . Metabolic acidosis
modulates lipid metabolism in adipocytes [111-114].
Acidosis reduces leptin concentrations in cultured adi-
pocytes . In uraemic Wistar rats, sodium bicarbon-
ate supplementation appeared to increase (but not
significantly) leptin levels . A study in chronic kid-
ney disease (CKD) patients with metabolic acidosis
revealed that serum leptin was significantly increased by
treating patients with a daily low to moderate dose
(0.05-0.2g/kg) of sodium bicarbonate. The report con-
cluded that either reversal of acidosis increases serum
leptin or metabolic acidosis masks serum leptin levels
Studies comparing serum leptin between healthy indi-
viduals consuming acidogenic type diets and those con-
suming more alkaline types of diets present mixed and
variable findings. A study in men and women compared
serum leptin levels between a group of 279 people con-
suming a diet rich in fish and a group of 329 people
consuming a strictly vegetarian diet. Fish consumption is
a high net acid producing diet . Both groups had
Robey Nutrition & Metabolism 2012, 9:72
Page 4 of 11
similar BMI values. The study was consistent with find-
ings from in vitro, and animal investigations in that it
reported the protein-rich diet was associated with sig-
nificantly lower levels of serum leptin than in individuals
on the vegetarian diet, independent of age . How-
ever, another study measuring serum leptin levels in over
50,000 healthy participants reported a positive correl-
ation with consuming a ‘Western’ diet, at least in the 5th
quintile of the study population . Other studies
have not observed an independent association between
dietary intake and serum leptin levels after adjusting for
energy intake, gender, age and BMI [117,118]. These
reports illustrate the deep and complex relationship be-
tween acidogenic diets and serum leptin concentrations
Physiological acidosis may indirectly influence leptin ac-
tivity through cortisol signaling in obesity which is a con-
dition predicted to be associated with dysregulated acid-
base balance . As discussed previously, acid-base sta-
tus affects cortisol levels . In turn, cortisol stimulates
synthesis and secretion of leptin directly from adipocytes
. Plasma leptin concentrations are positively corre-
lated to body fat mass in humans [120,121]. Leptin has
been shown to negatively regulate cortisol levels in healthy
mice and humans [122-125], implicating leptin as an anti-
obesity factor. In humans, leptin attenuation of cortisol
appears to be a greater factor in females . Serum lep-
tin levels are paradoxically high, however, in obese indivi-
duals. This phenomenon is likely due to an acquired
leptin signaling resistance that eventually occurs in the
obese state . On average, plasma leptin concentra-
tions are 10 times higher in obese individuals compared to
those of lean individuals [127,128].
Elevated plasma leptin levels in obesity may contribute
to cancer incidence . Leptin has been implicated as a
functional component of mammary carcinoma in wild-
type p53 deficient mice . Epidemiological, animal,
and in vitro studies have demonstrated that leptin is asso-
ciated with breast cancer, prostate cancer, gynecological
cancers, gastrointestinal cancers, and leukemia [131-133].
Leptin has numerous molecular targets allowing for a
multifunctional effect. Leptin functions as a mitogen and
is known to stimulate breast tumor cells, prostate tumor
cell lines, as well as colonic and hepatic cells. Leptin sig-
naling is most likely to activate the mitogen-activated pro-
tein kinase (MAPK) pathway through binding of Ob-Rb
leptin receptor [131-138]. Leptin may also enhance cell
proliferation through protein kinase C alpha (PKC-α)
[139,140]. Leptin has been shown to bind the estrogen re-
ceptor and stimulate estrogen biosynthesis by induction of
aromatase activity [141,142]. Other cancer-permissive
functional activities of leptin include promotion of angio-
genesis [143-145], apoptosis , and cellular migration
Acid-base balance may play a role in modulating serum
levels of adipokine hormone adiponectin. Adiponectin
regulates multiple metabolic processes and is expressed
exclusively in mature adipocytes and circulates in the
plasma . Numerous human and animal studies have
reported a strong correlation between diet and serum
adiponectin levels. Higher levels of serum adiponectin
are typically associated with the ‘Mediterranean’ diet,
known for high vegetable and fruit intake and low or
moderate amounts of meat consumption. Other nutri-
tional factors such as the amount and type of fatty acid
intake are thought to influence serum adiponectin, but
the mechanisms of diet-induced regulation of adiponec-
tin regulation are not fully understood . The first
and only study demonstrating the role of acid-base dis-
equilibrium in regulating serum adiponectin concentra-
tions was an interventional trial to measure levels of
serum adiponectin in healthy individuals induced with
transient metabolic acidosis. Twenty healthy females
completed a seven day course of oral ammonium chlor-
ide (NH4Cl), resulting in reduced serum bicarbonate and
subsequent reduction in adiponectin mRNA and serum
protein adiponectin. This was further confirmed in cul-
tured adipocytes where acidosis inhibited gene transcrip-
tion of adiponectin, suggesting a pH sensing mechanism
at the cellular level may influence the regulation of adi-
ponectin production .
Low serum adiponectin levels are considered to be
permissive for development of cancer [3,150]. Reduced
serum adiponectin levels are observed in patients with
breast and gastric cancers, and simultaneously linked to
dietary lifestyle [151,152]. Higher serum adiponectin
may be protective against cancer as an anti-proliferative
through direct binding of other growth factors, such as
platelet derived growth factor-BB (PDGF-BB), heparin-
binding epidermal growth factor-like growth factor (HB-
EGF), and basic fibroblast growth factor (basic FGF),
hence restricting bioavailability . This was demon-
strated in a mouse study where adiponectin was shown
to slow tumor growth through its inhibitory effect on
tumor neovascularization .
In addition to its interference with proliferative signal-
ing, adiponectin mediates its regulatory effects through
two receptors, AdipoR1 and AdipoR2 . Signaling
through these receptors stimulates the activity of adeno-
sine monophosphate-activated protein (AMP-k) kinase
and peroxisome proliferator-activated receptor alpha
(PPARα) which drives glucose uptake and fatty acid oxi-
dation. Through this mechanism, coupled with AdipoR1
receptor association with the insulin receptor, adiponec-
tin is proposed to enhance signal transduction to
promote insulin sensitivity . Although a greater
understanding is necessary, there is evidence suggesting
Robey Nutrition & Metabolism 2012, 9:72
Page 5 of 11
acid-base status maintained through dietary intake could
promote carcinogenesis or tumor progression through
dysregulated adiponectin signaling.
A very recent discussion about the role of diet-induced
acidosis and pathophysiology introduces the hypothesis
that persistent acidogenic or ‘Western’ diets lead to la-
tent or low-grade metabolic acidosis, subsequent acid-
base balance disequilibrium, and production of lactic
acid at the cellular level. These events appear to be crit-
ical upstream precursors to a host of ill-conditions, dis-
eases, and ageing. The premise further explains that
increased [H+] accumulates persistently in the mito-
chondrial matrix without contributing to ATP produc-
tion. This dynamic is theorized to inhibit mitochondrial
energy production (MEP) through inhibition of the TCA
cycle. MEP inhibition results in the diversion of elec-
trons away from completion of the electron transport
chain and toward the reduction of oxygen (O2) into re-
active oxygen species (ROS) such as free radical oxygen
species or peroxides [34,157]. As this cycle continues,
vulnerable cells develop a reduced capacity to restore
homeostatic balance and are subject to increased intra-
cellular oxidative stress.
The oxidative stress generated by ROS has multiple
effects causing damage to cellular and organelle mem-
branes, sulphydryl groups in proteins, and cross-linking
or fragmenting ribonucleoproteins and DNA. DNA mu-
tagenesis through persistent oxidative stress is generally
accepted as a major mechanism behind carcinogenesis
and cancer progression . Oxidative DNA damage
has been associated with breast cancer [159,160], hepa-
tocellular carcinoma and liver cancer [161,162], and
prostate cancer [163-165]. Oxidative stress in correlation
with obesity can manifest and have significant patho-
genic effects within the first two decades of life .
Although oxidative stress can be measured directly and
indirectly through various methods, it is far more diffi-
cult to differentiate between acidogenic diet-induced and
endogenous ROS production coupled with antioxidant
status and other molecular factors that may impact oxi-
dative steady state .
Although not fully understood, the long-term effect of
diet-induced acidosis is considered to have an impact on
bone osteoclasts . Serum [HCO3
may only partially account for neutralization of acidity,
and may be supplemented further by alkaline stores
from the soft tissue and bone . Osteoclastic resorp-
tion of minerals is a proposed mechanism in buffering
systemic acidosis [169,170]. In vitro findings demonstrat-
ing the mechanisms of excess [H+] on bone tissue is the
most reliable evidence currently driving the concept of
compensatory buffering through acidosis-induced bone
resorption. In cultured osteoclasts, lower pH conditions
induce the breaking up of mineralized bone tissue
matrix [171-175]. Bicarbonate [HCO3
sufficient to acidify media and promote net [H+] influx
into bone , and appears to be necessary (not just
reduced pH conditions which could be induced by re-
spiratory acidosis) to stimulate calcium [Ca2
Stimulation of osteoclastic resorption by diet-induced
acidosis is mediated through receptor activator of NFкB
ligand (RANKL) signaling . RANKL signaling is
known to promote osteoclast differentiation and acti-
vates various mitogenic pathways that are frequently
operational in tumor cells, including p38, MAPK, AP-1,
c-Jun, and Akt/PKB [179-182]. RANKL expression has
also been observed in lymphoid tissue, skeletal muscle,
thymus, liver, colon, intestine, heart, brain, and the ad-
renal and mammary glands . RANKL signaling has
been shown in mouse models to promote tumorigenesis
in breast and lung tissue . It is unknown, however,
if systemic acidosis induces RANKL activity in other cell
types besides osteoclasts.
One of the strongest RANK-stimulated transcription
factors in osteoclasts is the nuclear factor of activated
T-cells (NFATc1) protein [185,186]. Once exposed to
extracellular acidic pH, cytosolic [Ca2
clasts increase intracellular localization of nuclear tran-
scription factor NFATc1 through calcineurin signaling.
The ovarian cancer G-protein coupled proton-sensing
receptor (OGR1), which is induced during osteoclast
differentiation, is thought of as the primary mediator
between acidosis and NFATc1 activation. Calcineurin
signaling is not required however, to maintain NFATc1
activation under extracellular acidic conditions and
NFATc1 activity is reversed by extracellular alkaline
conditions, suggesting that acidosis directly prevents
NFATc1 inactivation by kinases . NFATc1 has
many functions in cancer  and has been linked to
regulation of the c-Myc oncogene [189-193]. Although
the link between acidosis and RANK/NFATc1 mediated
carcinogenesis or tumor promotion is not established,
chronic activation of these factors through a dietary
induced state of dysregulated acid-base status may con-
tribute to cancer risk.
-] deficiency may be
+] efflux from
+] stores in osteo-
This work examines the potential for cancer risk or
tumor promoting consequences of diet-induced acidosis.
Although protein is a major factor involved in promot-
ing endogenous acid production, it should be made clear
that attenuation of protein consumption is not a recom-
mended dietary strategy for attaining improved acid-
Robey Nutrition & Metabolism 2012, 9:72
Page 6 of 11
base balance. There is scientific evidence supporting the
concept that appropriate alkali supplementation in the
form of fruits and vegetables serves aptly to neutralize
excess [H+] produced from protein metabolism [34,194].
The analysis provided discusses how diet-induced acid-
osis is a potential upstream and indirect trigger in a
multifactorial cascade of molecular events associated
with carcinogenesis. There is limited evidence to sug-
gest that dietary acidosis alone is sufficient in increas-
ing cancer risk, but it may function in concert with
other factors associated with cancer risk. Obesity or
metabolic syndrome, which effect glucocorticoid and
adipokine profiles and are often linked to insulin re-
sistance and the pro-inflammatory state, could also
serve as significant factors as they are associated with
both acidogenic or ‘Western’ diet  and cancer risk
In conclusion, there are numerous systemic pathways
affected by diet-induced acidosis that may be cancer
promoting, but a causal role is poorly defined. Moreover,
the contribution of diet-induced acidosis in driving car-
cinogenesis would be difficult to measure especially
since the effects appear to accumulate for a long period
of time. Nonetheless, exploring the role of dietary
induced acidosis involvement in molecular pathways
that promote carcinogenesis will raise new questions
and foster ideas to improve our understanding on the
role of acid-base balance in human disease.
IGF-1: Insulin growth factor; GLUT: Glucose transporter; IDO: Indoleamine 2,3-
dioxygenase; TDO: 2,3-dioxygenase; APC: Antigen presenting cell; AHR: Aryl
hydrocarbon receptor; ROS: Reactive oxygen species; CKD: Chronic kidney
disease; BMI: Body mass index; PDGF-BB: Platelet derived growth factor-BB;
OGR1: Ovarian cancer G-protein coupled proton-sensing receptor;
NFATc1: Nuclear factor of activated T-cells; AMP-k: Adenosine
monophosphate-activated protein kinase; PPARa: Peroxisome proliferator-
activated receptor alpha; MEP: Mitochondrial energy production;
MAPK: Mitogen-activated protein kinase; 11ßHSD2: 11ß-hydroxysteroid
dehydrogenase 2; HB EGF: Heparin-binding epidermal growth factor-like
growth factor; RANKL: Receptor activator of NFкB ligand; OGR1: Ovarian
cancer G-protein coupled proton-sensing receptor; NFATc1: Nuclear factor of
activated T-cells; AMP-k: Adenosine monophosphate-activated protein kinase;
PPARa: Peroxisome proliferator-activated receptor alpha; MEP: Mitochondrial
energy production; MAPK: Mitogen-activated protein kinase; 11ßHSD2: 11ß-
hydroxysteroid dehydrogenase 2; AICR: American Institute for Cancer
The author declares that he has no competing interests.
IR conceived and drafted the manuscript in its entirety and approves the
National Centers for Complementary and Alternative Medicine, NIH grant
Received: 24 April 2012 Accepted: 27 July 2012
Published: 1 August 2012
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Cite this article as: Robey: Examining the relationship between diet-
induced acidosis and cancer. Nutrition & Metabolism 2012 9:72.
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