Acid-Base Balance: Myths and Realities

Posted By elissa on May 9, 2008 | 6 comments

If you Google terms like “alkaline diet” or “alkalizing foods” – you’ll come up with page after page of some of the loopiest stuff imaginable.  One site proclaims that an “acidic, anaerobic” body encourages the growth of “fungus, mold, bacteria and viruses.”  Another provides a laundry list of non-specific symptoms of “acidification” and suggests that stimulants such as “coffee, tea and alcohol” are “extremely acidifying.”  Often, sites will include lists of acid and alkaline foods…and if you compare lists, they don’t always match.  And needless to state, no one tells you where this information comes from.  Are the authors relying on scientific studies?  Something they read in a holistic health magazine written by a “nutritionist” with vague credentials and training?  Pulling it out of their you-know-where’s?   Who knows?  In addition, many of these sites – not coincidentally – have diverse “alkalizing” supplements and cure-alls to sell you…such as wheatgrass juice, potassium/sodium hydroxide drops, goat whey, cesium chloride and alkaline water.

There is, however, a reality behind the hype.  The subject of acid-base balance is one of increasing concern to researchers studying osteoporosis and sarcopenia (age-related muscle wasting).  Both of these conditions are associated with aging.  Maintaining a proper acid-base balance may be the key to preventing both.

Before digging in deeper, it will help to have some background…what do we mean by acid-base balance?

The measurement that defines acidity, pH, is a way of assessing the number of free H⁺ molecules (hydrogen ions) in a solution. pH is expressed as a number between 1 and 14: 7.0 is neutral,  below 7.0 is acidic, and greater than 7.0 is basic (or alkaline). The pH of blood is slightly alkaline, around 7.4. The body requires a relatively constant pH to function properly. Changes in pH can affect the ionization of the molecules participating in important physiological reactions.  Even relatively small changes would be sufficient to shut down many processes, and could result in coma, or even death. The pH of the blood must be maintained within a very narrow range, + 0.3, to function normally.

In other words, “acid-base balance” is about maintaining your blood at an optimal pH – which is ever-so-slightly alkaline.

So where does diet fit into all of this?

Unfortunately, our Western-style diet presents a challenge to our bodies’ ability to maintain itself at the correct pH level.  Researchers have identified three culprits: cereals/grains, animal proteins, and salt (sodium chloride).  Diets dominated by these foods create a condition known as chronic metabolic acidosis (CMA). A more severe form of this syndrome occurs in kidney disease. As kidney function deteriorates, the ability of the body to eliminate metabolic wastes is affected. Some of these waste products are acids. As they build up in the bloodstream, the normal, slightly alkaline pH of the blood changes. The results are devastating. According to one summary:

“Metabolic acidosis induces nitrogen wasting and, in humans, depresses protein metabolism. The acidosis-induced alterations in various endocrine systems include decreases in IGF-1 levels due to peripheral growth hormone insensitivity, a mild form of primary hypothyroidism and hyperglucorticoidism. Metabolic acidosis induces a negative calcium balance (resorption from bone) with hypercalciuria and a propensity to develop kidney stones. Metabolic acidosis also results in hypophophataemia due to renal phosphate wasting. Negative calcium balance and phosphate depletion combine to induce a metabolic bone disease that exhibits features of both osteoporosis and osteomalacia.”

The effects of diet-induced CMA are more insidious. The damage occurs in small increments, much like the effects of erosion. Over time, however, the cumulative effects become impossible to ignore. As noted above, low-grade CMA has been implicated in many of the symptoms associated with aging: loss of bone, muscle wasting, formation of kidney stones, depression of thyroid hormones, and an increase in cortisol secretion.

So how do cereals/grains, animal proteins, and salt contribute to CMA?  These foods release a variety of compounds during their breakdown, including sulfuric acid, derived from the metabolism of sulfur-containing amino acids in proteins, and phosphoric acid, released from animal protein foods, grains, some nuts, and mature legumes (there are also some foods where phosphoric acid may be consumed directly, such as regular or diet colas). Chloride (Cl-) anions from table salt contribute to acid levels as well. 

Blood contains a variety of compounds that are able to “buffer” excess acid.  The primary buffer system in the blood is the bicarbonate buffer system. Carbonic acid (H₂CO₃) acts as a hydrogen (proton) donor, and hydrogen carbonate (HCO₃^–) acts as a hydrogen acceptor. The amounts of each component are regulated via two separate systems. Carbonic acid levels are regulated via respiration. Excess carbonic acid is converted to carbon dioxide gas by an enzyme, carbonic anhydrase, and exhaled from the lungs. Excess hydrogen carbonate is filtered through the kidneys and excreted in urine. Hydrogen carbonate is present in much higher quantities than is carbonic acid; this gives the body the ability to take up excess protons, and eliminate them in the form of carbon dioxide and water.

If excess acid is produced, an increased amount of hydrogen carbonate is lost. If the carbonate is not replaced by the diet, it must be taken from the body’s own stores. The main storage depot for carbonate is the skeleton.

In other words, our bones represent a sort of “safety valve,” against excess acidity.

Thanks to our bones, our bodies have the means to counteract acidosis, but that protection comes at a price. Bone is composed primarily of calcium carbonate, calcium phosphate, collagen (structural protein) and water. Bone modeling and remodeling is conducted by specialized cells known as osteoblasts and osteoclasts. Osteoblasts are involved in bone formation, while osteoclasts are involved in bone resolving. Normally, a balance exists between the two activities: osteoclasts dissolve older bone, while the osteoblasts replace it. Bone weakening occurs when the rate of bone resorption by osteoclasts exceeds the rate of bone modeling by osteoblasts.

Metabolic acidosis accelerates bone resorption by two mechanisms. Initially calcium losses occur through physicochemical dissolution of bone minerals. This is followed by stimulation of osteoclast activity and depression of osteoblast activity. These changes lead to pit formation in the bone, and destruction of the organic matrix.  Unchecked, these processes weaken the bones, and accelerate the onset of osteoporosis.

The damage caused by CMA isn’t limited to bone – muscle is also compromised.  Muscle breakdown, or proteolysis, is a homeostatic response to acidosis.  Muscle proteolysis releases the amino acid glutamine, which can then be used by the kidneys to produce ammonia. This conversion allows increased excretion of protons in the form of ammonium.  Glutamate is also used to consume surplus protons via conversion to glucose and urea.  

Important hormones are also affected to some degree.  The metabolic acidosis that accompanies kidney disease is known to cause increases in glucocorticoid hormones (cortisol, ACTH), decreased secretion of growth hormone (GH) and insulin-like growth factor-1 (IGF-1); decreased secretion of parathyroid hormone (PTH); decreases in free T3/T4 thyroid hormones and an increase in thyroid stimulating hormone (TSH). These hormones all play a role in growth and body composition. The impact of milder, diet-induced acidosis on these hormones is less pronounced, but still significant. Diet-induced acidosis is considered “…part of an endocrine-metabolic continuum that includes…moderate to severe CMA.”

The good news is that it’s possible to correct CMA and arrest – or even reverse – the negative changes.  Impressive results have been achieved with experimental bicarbonate supplementation. In one study,  60 – 120 mmol/day of orally administered potassium bicarbonate reduced endogenous acid production in post-menopausal women to zero. Furthermore, the researchers calculated that the decrease in nitrogen excretion during the experimental period – if maintained over a year – would result in a net gain of 2.0 kg (4.4 lbs.) of lean body mass – equivalent to “…a restoration of about 1 decade of muscle mass decline.” In another study, oral potassium/sodium bicarbonate supplementation dramatically increased calcium retention, while decreasing markers of bone resorption (deoxypyridinoline, pyridinoline, and n-telopeptide), and plasma cortisol levels. This research was particularly striking in that the study subjects were young (22.1 + 1.4 years) adults still undergoing bone growth.  In a more recent study, potassium citrate was also shown to be effective for increasing bone mineral density and reducing calcium excretion (citrate is a metabolic precursor to bicarbonate).

Could similar benefits be obtained through diet alone? Are there foods that can supply the body with a sufficient amount of alkaline salts to neutralize the effects of dietary acidosis?

The answer just might be yes.

Over the last decade, Thomas Remer and Friedrich Manz developed and validated a calculation model to estimate the renal net acid excretion (NAE) produced by various foods.  Their calculations were based on the principal non-bicarbonate anions (sulfate, phosphate, chloride, and organic acids) and cations (sodium, potassium, calcium, and magnesium) in foods and validated using human subjects consuming different diets. Although their full list of 118 foods is far from comprehensive, it is sufficient to establish a pattern: fruits, vegetables, juices, and alkali-rich, phosphorus-poor beverages have the lowest (negative) scores. The scores increase towards neutral for alkali-poor, low-phosphorus beverages, fats and oils, and become positive for milk and non-cheese dairy products, and grain foods such as bread and noodles. Meat, poultry, fish, egg yolks and cheeses are the foods with the highest values.

In other words, while the positive scoring, high protein and grain foods contribute acids, other foods – primarily vegetables, herbs, and fruits with negative scores – produce alkaline metabolites that can counteract them and prevent acidosis from developing. 

Unfortunately, veggies and fruits are precisely the foods that are displaced in modern, Western diets.  Surveys consistently show that a majority of Americans don’t meet even the minimum dietary recommendations for vegetable/fruit consumption.

Can consuming more veggies and fruits prevent – or at least mitigate – the effects of CMA? A number of studies suggest it can. Several epidemiological surveys have been conducted that firmly link higher consumption of alkali-rich vegetables and fruits with lean body mass and indices of bone health in older (ages 69 – 97) and middle-aged adults; pre- and perimenopausal women, and even adolescent girls. Researcher and author Loren Cordain’s retrospective studies on the origins of the Western diet and characteristics of the diet(s) preagricultural Homo sapiens stress the importance of acid-base balance in the development of “diseases of civilization.” While the life-spans of our ancestors were reduced by infectious diseases, accidents, and childbirth, paleo-anthropologists have concurred that they were remarkably free from degenerative diseases, thanks, in large part, to diets that were “net base yielding” and had a low sodium/potassium ratio.

So beyond the confusion and often contradictory information you see, a genuine problem exists.  Fortunately, it’s not necessary to adopt unusual food rituals nor buy expensive supplements.  Eating plenty of vegetables and fruits, and reducing excess salt intake are ultimately the keys to reducing CMA.