A correct acid-base balance is essential for good health. Numerous enzymatic reactions depend on the intra- and extra-cellular pH remaining within a narrow range. Deviation from this norm can lead to a number of health problems. Our dietary habits tend to tip the balance towards acidification. Eating a more balanced diet, exercising and taking mineral- and plant-based alkalinising nutritional supplements often help restore the balance.
In medical terms, acid-base balance refers to the blood pH (potential of Hydrogen) which must be maintained at a level close to 7.4 (slightly alkaline or base).
Regulating acid-base balance
Such is the importance of acid-base balance in blood and tissues that numerous biological functions are involved in its regulation, including respiration, excretion, digestion and cellular metabolism. Substances called buffers act chemically to prevent pH changes in the blood. The most important of these are bicarbonate, albumin, globulin and haemoglobulin.
The kidneys also react to blood pH. If it is too acid, they excrete excess hydrogen via the urine and retain excess sodium. Phosphorus, in its phosphate form, is essential for this exchange. The body obtains it from the bones when it is not available elsewhere. When the blood is extremely acid, the kidneys use a different method, excreting ammonium ions via the urine. When the body is too alkaline, the process is reversed to retain hydrogen ions.
The lungs also play a part in regulating acid base balance by eliminating carbon dioxide from the blood. The carbon dioxide combines with water in the body to form carbonic acid, so that eliminating the carbon dioxide also eliminates the acid. The respiratory rate can vary according to the body’s acidity, speeding up in acid conditions to eliminate carbon dioxide, and slowing down in alkaline conditions to retain acids and reduce alkalinity. Just as the blood flow’s pH is strictly controlled, so the acid-alkaline environment of the cell’s interior is also regulated within a tight range. This regulation takes place by means of pumps in the cell membranes which allow hydrogen to enter or leave the cells. Most of these pumps need phosphorus and magnesium in order to function. The pH of the cell’s interior can also be regulated via chemical reaction changes producing variable quantities of hydrogen.
Evaluating your body’s acidity or alkalinity
The easiest way is to test the pH of your urine with pH strips. The strip instantly changes colour on contact with urine, each colour corresponding to a pH. The first urine of the day may have a pH of 5 or even lower. The body gets rid of acidity during sleep. During the day, a healthy pH reading should be between 7 and 7.5.
Reactions that regulate acidosis or alkalosis
In the case of acidosis, the blood pH is too acid (lower than 7.35). In this case, the blood’s buffering systems will act to shift the pH towards alkaline and the respiratory rate will increase to eliminate carbonic acid via carbon dioxide exhalation. The kidneys will then increase urine acidity and the balance will be restored.
Acidosis is not caused by the absorption of acid foods such as lemons or oranges, but is usually the result of problems with metabolism, such as diabetes or starvation, kidney diseases or respiratory disorders that restrict the release of CO2 by the lungs.
Alkalosis, which is less common than acidosis, can result from hyperventilation (breathing too fast), a loss of stomach acid caused by excessive vomiting, or overuse of antacids or ulcer medication. In this case, the blood’s buffering system will adjust in favour of acid, breathing will slow down to conserve CO2 and increase blood levels of carbonic acid. Again, the kidney help restore balance by excreting less alkaline urine.
A tendency towards acidity
These regulatory reactions work when we are in good health. The body’s natural tendency, however, is to tip the balance towards acidity. Our own metabolism constantly produces acid waste products which are basically eliminated by the lungs and kidneys. When these organs are not functioning properly, under the influence of acidifying factors, acid production becomes excessive and waste products are relocated into connective tissue in order so that a normal blood pH value is retained. This acidification process can lead to chronic tissue acidosis which accelerates the ageing process and creates an environment conducive to the development of a number of diseases.
Acid chemistry/basis of digestion
The cells of the stomach wall secrete hydrochloric acid. This is strong enough to cause a mild burning sensation when placed on the skin but the stomach is protected by mucus secreted by other cells. Hydrochloric acid has two important functions: it has a direct effect on food, essentially proteins, initiating the breaking down process called hydrolysis, and facilitating the work of an important enzyme, pepsin. When there is insufficient hydrochloric acid, pepsin is inactive resulting in poor digestion.
A normal stomach pH is somewhere between 1.5 and 2.5 (ie very acid). It is neutralised to some degree by the food it absorbs but the stomach is capable of re-acidifying during a meal to end the digestive process. During this time, food is reduced to a semi-liquid mass called chyme, the pH of which is much less acid - between 3.5 and 5, ready to cross into the small intestine.
The digestive process continues in the small intestine with the help of enzymes secreted by the pancreas, gallbladder and intestinal wall. But here there is a fundamental difference. While the initial stage of digestion in the stomach requires a strongly acid environment, the later stages require alkalinity. This is why 90% of all absorption happens in the small intestine and why its absorbent tissue is extremely sensitive. This rapid and significant change to an alkaline pH takes place in the pancreas which secretes necessary quantities of bicarbonate. In fact, the pancreas may produce the equivalent of 6 Alka-Seltzer tablets a day. Digestion is thus a complex and finely-tuned
process, involving reaction mechanisms between the stomach and pancreas to maintain optimal acid/base levels. Excessive use of any medication that may alter this balance is potentially harmful.
Acidifying or alkalinising foods
The diet provides hydrogen ions (acids) and bicarbonates (base). Depending on whether the hydrogen ions predominate or not, the blood will be either more or less acid.
Excessive acidity in the blood can increase the risk of osteoporosis, diabetes, atherosclerosis, hypertension and certain cancers.
At the final stage of energy production, the mineral content of food is not oxidised. It therefore leaves either an alkaline, acid or neutral residue depending on the mineral make-up of the food. Sulphur, phosphorus and iron form acid ions in the body. These minerals are mostly found in protein sources such as meat, fish, eggs, chicken, cereals or nuts. These foods are therefore acidifying foods. Potassium, calcium, magnesium and sodium form alkaline reactions in the body. They are mostly found in fruits and vegetables and are thus termed alkalinising foods or base generators.
It is all a matter of balance. For example, milk is high in protein, sulphur and phosphorus so you might think it is an acid-forming food. But it contains enough calcium to produce a balance and to be almost neutral. Each person’s metabolism and digestion also play a determining role in whether a food leaves either an alkaline or acid residue. For example, foods containing organic acids such as lemons or tomatoes would not normally leave acid residues but in certain individuals, they may not be completely metabolised and in such circumstances, they become acidifying foods. This is often the case when levels of stomach acids are low or when thyroid activity is disturbed.
Other elements affect this balance
Metabolic or lifestyle factors also affect our body’s acidity and reactions to different foods. Infections, smoking and alcohol tend to make the body more acid. In addition, the diet’s trace-element content affects acid-base balance. Adequate intake of magnesium and phosphorus are needed in order for cellular pumps to work properly. Zinc is essential for acid secretion in the stomach and for the retention or excretion of acid by the kidneys. Other nutrients such as the B vitamins play a crucial role in fully metabolising carbohydrates and fats.
Consequences for our health
In the past, it was thought that the acid- or base-forming properties of our diet were only important for patients suffering from kidney stones
. An alkaline diet, with lots of fruit and vegetables, produces more alkaline urine and was used to treat uric acid stones, while an acidifying diet rich in meat, fish and cereals, was used for oxalate stones.
Osteoporosis and acid-base balance
The best example of the harmful effects of an over-acidifying diet is probably that of acid/base factors on bone health. Acidosis accelerates catabolic damage and upsets the process of anabolic repair.
It has long been acknowledged that a protein-rich diet increases the risk of osteoporosis. Epidemiological studies have suggested a link between consumption of animal protein and osteoporosis. Research shows that those who eat more fruits and vegetables have higher bone density. Studies have also noted a three- to five-fold risk of fractures among adolescents who regularly consume soft drinks.
The urine of vegetarians is more alkaline than that of carnivores. In the latter, the acidity comes from the metabolism of sulphur amino acids; consumption of fruits and vegetables in combination with meat enables urine pH balance to be restored. Intake of acidifying or alkalinising foods affects the bones because the skeleton plays a role in the acid-base balance by supplying calcium, amongst others, every time excess acid is present.
When the body does not produce eliminable acids (particularly through a lack of vitamins and oligo-elements) or when there is an overload of total acidity (dietary and metabolic acids), this excess is stored in the connective tissue, which collects the acid waste products that the lungs and kidneys have been unable to get rid of. If these excess acids are not eliminated, they build up year after year in the connective tissue: this is chronic tissue acidosis which affects oxygen transport and cell nutrition and prepares the way for the development of disease.
One study investigated the potential benefits of an alkalinising treatment for individuals with dietary-induced mild metabolic acidosis. Experimental and epidemiological data support the notion that alkalinising foods have a beneficial effect on bone health while an acidifying diet has a harmful effect, increasing the risk of fracture. In effect, the acidosis boosts activity of the osteoclasts responsible for bone resorption and inhibits that of osteoblasts, and as a consequence, bone formation. In metabolically-controlled studies in healthy menopausal women, supplementation with potassium bicarbonate, which only slightly increases plasma bicarbonate levels maintaining them within normal values, almost halted urinary excretion of acids in an immediate and reversible manner. At the same time, calcium and phosphorus balance was restored. These findings lead the researchers to think that an increase in fruit and vegetable consumption or an alkalinising supplement may prevent or delay the onset of osteoporosis, muscle loss and calcium-containing kidney stones by preventing or correcting the mild acidosis present in elderly individuals.
Restoring the balance
Restoring the body’s acid-base balance involves the application of appropriate dietary advice, oxygenation and alkalinising nutritional supplements.
The diet should include more alkalinising foods such as fruits and vegetables and fewer acidifying foods such as meat, fish or cereals.
Physical exercise, especially outdoors, that gets the heart rate up and stimulates diuresis also helps restore the balance.
In some cases, however, changes to diet and lifestyle will not be enough to remedy tissue acidosis. In such cases, alkalinising plant- and mineral-based nutritional supplements are essential in order to restore acid-base balance.
Sebastian A. et al., Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate, New Engl. J. Med., 1994; 330: 1976-81.
Susan E. et al., Acid-alkaline balance and its effect on bone health. International Journal of integrative
medicine, vol 2, n°6, Nov-Dec 2000.
Curtis R. et al., Alkali therapy in renal tubular acidosis: who need it ? J. Am. Soc. Nephrol. 13; 2186-2188, 2002.
Lemann J. Jr et al., The effect of chronic acid loads in normal man: further evidences for participation of bone mineral in the defense against chronic metabolic acidosis. J. Clin. Invest. 45: 1608-1614, 1966.
Bushinsky D.A. et al., Acid-base imbalance and the skeleton, in : Nutritional aspects of osteoporosis, Sereno symposia, SA Publication edn. Edited by Burckhardt P., Dawson-Huges B., Heaney R.P., New Yok, Springer verlag, 1998, p. 208-217.
Preminger G.M. et al., Prevention of recurrent calcium stone formation with potassium citrate therapy in patient with distal renal tubular acidosis, J. Urol. 134: 20-23, 1985.
Frasseto L. et al., Potassium bicarbonate reduces urinary nitrogen excretion in postmenopausal women. J. Clin. Endocrinol. Metabol. 82: 254-259, 1997.
Frassetto L.A. et al., Effect of age on blood acid-base composition in adult human: a role of age-related renal functional decline. Am. J. Physiol. 271: F1114-F1122, 1996.