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The Acid-Base Equilibrium
In Human Health
Optimal growth and development are only attainable when there is a well-balanced inner
environment. One of the most important features of homeostasis is regulating the body’s
acid-base balance. It is the equilibrium of acid-alkalinity status in our bodies that permits the
optimum function of all major metabolic processes essential to life.(1)
The Acid-Base Balance Complexity
The physiology of acid-base homeostasis is complex, involving
different body compartments and a range of biological
buffering systems. Each day our normal process of metabolism
creates acid as non-volatile sulfate from amino acid catabolism,
non-metabolised organic acids, and phosphoric and other
acids.(2) In order to maintain the body’s acid-base balance,
Diet
Intestine
Regulates bicoarbonate
levels & moderates
alkali reabsorption from
pancreatic secretions
AA-S
OA
Liver & other tissues
Blood
Acid-Base
Pool
Lung
Regulates the bicarnobatecarbonic acid buffer
system via respiratory
compensation
Kidney
Reabsorbs the
filtered bicarbonate
generating new
bicarbonate in the
collecting duct &
eliminates alkali ions
Figure 1: A basic representation of the organs involved in the
regulation of acid-base balance within the body
different systems intrically interreact with one another, and
individual organs stimulate a series of reactions to support the
correct equilbrium.(3)
For instance, after food consumption, in the gastrointestinal
system the role of the intestine is to regulate the blood’s
bicarbonate levels by modulating how much alkali from
pancreatic secretions is reabsorbed. The absorption of sulfurcontaining amino acids (AA-S) and alkali salts (of metabolizable
organic acids - OA), and their consequent availability in the liver
and other tissues, is controlled by the gut.(3) The renal system is
involved in controlling the excretion of alkali ions (bi-products
of sulphur amino acid and organic acid oxidation) released into
the blood. The respiratory system controls the carbonic acidbicarbonate buffer system and therefore, through the process
of respiratory compensation, the blood pH keeps within its
correct range.(3) (Figure 1)
The body’s own natural buffering systems are generally able to
regulate changes in blood pH, thus preventing major changes
in cell function.(4) Buffers can include intracellular proteins such
as haemoglobin, tissue components such as calcium carbonate
and calcium phosphate in bone, as well as the bicarbonatecarbonic acid buffer pair generated by the hydration of carbon
dioxide. The bicarbonate-carbonic acid buffer pair is generally
considered most critical, since any alterations of this can affect
all other buffer systems in the body.(5)
In healthy humans, homeostatic mechanisms and the body’s
ability to regulate the pH inside and outside of the cells is
essential for optimal enzyme-controlled metabolic processes.
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Many factors can alter the acid-base balance, directly
influencing enzymatic reactions and the regulation of
metabolites within the body.(5) It is difficult to exactly measure
the acid-base status of a patient, unless there is a specific
metabolic disturbance causing significant alterations to blood
pH, such as those expressed in cases of acute or chronic acidosis
or alkalosis.(6) However, often a patient’s acid-base balance is in
disequilibrium, without any major alterations to extracellular
pH or buffering capacity, rendering any testing irrelevant.(6)
Acidosis versus Alkalosis
Acidosis (a state of extreme acidity) and alkalosis (extreme
alkalinity) are abnormal conditions.(1)
Acidosis can include metabolic and respiratory types, though
research also highlights renal tubular acidosis.(2) The primary
basis for metabolic acidosis is excessive production of acid.(2)
Table 1 lists some of the causative factors for this high-grade
acid load. Respiratory acidosis, generally caused by retention of
carbon dioxide, is commonly associated with ventilatory failure
and chronic pulmonary diseases.(5)
Table 1: Causative Factors for Metabolic Acidosis
A high consumption or
Insufficient bicarbonate
generation of organic
production(2)
(2)
acids
Anaerobic metabolism
Renal disease or chronic
due to shock or cardiac
renal failure(5)
(5)
arrest
Diabetic ketoacidosis(5)
Loss of bicarbonate ions
from the gut or kidneys(5)
Diarrhoea(2)
Biliary fistula(2)
Research suggests that renal tubular acidosis is most
commonly associated with severe health conditions, such
as Systemic Lupus Erythematosus and Sjogren’s syndrome.
However, evidence further stipulates that fevers, urinary tract
obstruction, deficiency in aldosterone, and the administration
of glucocorticoid steroid drugs can also induce this type of
acidosis.(2)
Furthermore, chronic acidosis can lead to a dampening
of activity within the central nervous system, with the
manifestation of symptoms such as headaches, lethargy,
weakness and confusion.(5)
High intensity exercise causes high serum levels of lactic acid
and metabolic acidosis, physically manifesting as muscle
fatigue, cramping and exhaustion. Research proposes that
one way to prevent exercise-induced acidosis is with alkali
supplementation, suggesting that improved muscular
performance may be achieved by increasing the buffer capacity
of the body.(7)
Conversely, uncontrolled alkalosis can induce overactivity
of the nervous system, expressed as restlessness, irritability,
muscle twitching, tingling and/or numbness of the
peripheries, and seizures.(1) Alkalosis can be induced through
hyperventilation (respiratory alkalosis) resulting from stress
or anxiety, high fevers, or over-medication with non-steroidal
anti-inflammatory drugs. Metabolic alkalosis, marked by
increases in serum bicarbonate ion, occurs from a number of
factors. These may include hydrochloric acid depletion from
the stomach because of vomiting or drainage, severe intestinal
obstruction, hypokalaemia, or antacid medication ingestion.(5)
Both acidosis and alkalosis can co-exist, particularly if an
individual has respiratory disease, renal disorders and/or
metabolic disturbances.(4)
The Influence of Nutrition on Acid-Base
Equilibrium
Nutrition is widely recognised as one of the most important
factors that can directly impact an individual’s acid-base
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equilibrium. Studies undertaken as far back as the early 1700’s
highlighted the relevance of dietary consumption to the body’s
acid-base balance.(7)
How does food itself impact the acid-base equilibrium?
Evidence suggests that the actual composition of foods
contributes either a net acid or base effect to the body. In
very general terms, an acid load or base effect occurs from
the balance between (i) acid-forming elements in foods – for
example, sulfuric acid that results from the reduction of cysteine
and methionine in dietary proteins – or, (ii) base-forming
elements in food, such as bicarbonate that comes from the
metabolism of organic anion potassium salts in plant foods.(2)
Today, studies show that humans tend to consume diets that
generate high levels of metabolic acids, leading to a reduction
in pH and a dysregulation of the acid-base balance.(8) It is
suggested that human tendency towards an acidic state is
largely due to a dietary absence of elements such as potassium
alkali salts (K-base), generally found in plant foods.(2)
Acid diet Systemic acidity Increased systemic acidity Decreased acid excre/on from the body Decline in kidney func/on In terms of the current quality of foods, the use of highly
processed inexpensive non-perishable food products, coupled
with poor dietary habits, has resulted in epidemics of nutritional
disorders throughout the modern world. Epidemiologic
studies have found that the absence of vitamins or trace
elements accounts for a high proportion of dietary induced
metabolic disorders.(7)
Increased acid secre/on into the system Increased mineral excre/on via kidneys Figure 2: Effects of an Acid Diet
Generally, and under normal steady-state conditions, dietinduced low-grade metabolic acidosis produces a slight
decrease in blood pH and plasma bicarbonate that still sits
within a normal pH range. Whilst within this range, the
body equilibrates closer to the lower end of the normal pH
range instead of calibrating toward the higher end of the
normal range. However, even low-grade acidosis can have
severe metabolic consequences if it remains at a constant
and long-term state.(2) Diets that generate a higher acid load,
in conjunction with a natural age decline in kidney function,
are the two main factors that render the body less capable of
excreting metabolic acids, which then leads to a greater risk for
the development of chronic metabolic disorders.(8)
Research proposes that dietary changes and alkaline nutrient
supplementation may assist in normalising states of chronic
low-grade acidosis. Specifically, the kind and quantity of
proteins, fruits and vegetables consumed can influence the
net acid load in the body. Evidence has shown vegetarian
diets to have a consistently lower endogenous acid production
than diets consisting of higher, or even moderate amounts of
protein. Supplementing with alkaline nutrients and increasing
intake of fruits and vegetables are associated with a more base
producing diet.(2)
The effects of dietary acid load is often overlooked in subjects
presenting with disturbances of acid-base metabolism.
However, because the body’s natural adaptation mechanisms
(via the renal, endocrine, and musculoskeletal systems) impose
an enormous burden in cumulative organ damage over
time, dietary influences can no longer be ignored as a major
influential factor.(9)
Several studies report on the pathophysiological effects of long
term acidosis and how this affects multiple body systems.
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In children, severe metabolic acidosis has been associated with
decreased hormone growth levels. In these cases, children
show visible signs of stunted growth and development, often
expressed as depressed height and weight, bone weakness and
lowered levels of Insulin Growth Factor-1 (IGF-1).(9)
Decreased bone and muscle mass in adults is a welldocumented consequence of severe metabolic acidosis. A
large reservoir of base is found in the bones, in the form of
alkaline salts of calcium (phosphates or carbonates). During
increased acid loads, the body’s natural response is to mobilize
these salts and release them into systemic circulation. Once
acid-base homeostasis is achieved, these released calcium
and phosphorus salts are then excreted in the urine. As a larger
metabolic consequence, there is reduced bone mineral content.
In a state of ongoing acidosis, the skeletal system continues
its natural buffering process in order to maintain acid-balance
homeostasis, a process that then becomes detrimental to bone
mineral content and bone mass.(9)
A strong association between acidosis and enhanced pain
perception has not yet been conclusively determined. However,
studies have found that local tissue acidosis in subjects with
complex regional pain syndrome leads to enhanced pain
sensation.(2)
The relationship between insulin resistance and the acid-base
equilibrium is still unclear. In human studies, insulin resistance
has been linked to decreased excretion of urinary citrate. It is
suggested that hypocitraturic subjects have a higher degree
of insulin resistance compared to controls. Additionally, it is
well documented that renal function can be compromised in
diabetes mellitus patients. The risk of uric acid stone formation is
higher in these subjects as a result of impaired renal ammoniagenesis, which causes a lower urinary pH.(2)
Cardiometabolic risk factors, such as changes to blood pressure,
cholesterol and obesity, have been associated with mild
metabolic acidosis. Research suggests that this may be due to
increases in cortisol production, calcium excretion or decreased
citrate excretion. In 2008, a study examining the associations
between diet induced acid load and the risk of cardiometabolic
disorders in women, found that acidic dietary loads were
positively associated with higher systolic and diastolic blood
pressure, as well as increased LDL-cholesterol, basal metabolic
index (BMI) and waist circumference.(10)
In summary
In science, there appears to be a unifying concept to describe
acid-base balance, which is stated as : “The evolution of acidbase equilibrium is geared to maintain the structural and
functional integrity of proteins in the presence of unavoidable
changes in body temperature, osmolarity and ionic strength”.(7)
The manifestation of severe metabolic disturbances resulting
from dietary-induced alterations to the human acid-base
equilibrium presents a real challenge to health practitioners.
Dietary-induced acidosis is a real phenomenon with
significant clinical relevance. Being able to understand the
various mechanisms involved in acid-base metabolism and
recognising the influencing factors may help to identify the
early signs of metabolic disturbances before the onset of more
severe disorders. Both dietary interventions and nutritional
supplementation with base forming minerals have been
shown to normalize acidosis and support a more optimal acidbase balance within the body.
References available on request.
This information is for healthcare practitoners only
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