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Using pH as a measure of Digestive Physiology

by Peter Bartlettt(more info)

listed in colon health, originally published in issue 13 - July 1996

Proper digestion is a prerequisite for optimum health. Ascertaining the degree to which digestion has become dysfunctional is critical, as abnormal digestive physiology adversely affects enzyme and nutrient assimilation.

There are three major aetiological factors in the development of such disturbances (and therefore of all disease), namely “defensive physiology”, mental/ emotional stress and toxic overload. Let me explain.


“Defensive physiology” refers to the way in which the body responds reflexively to repeated stimuli, which if noxious, can create real, physical changes in the individual’s muscular-skeletal, neurological and immune systems, so that their physiology becomes distorted and operates out of phase with their environment and adapts unsuccessfully to the stress. It is highly probable that mental and emotional stress will have, in many cases, far more negative effect on the patient’s homeostasis than either of the other two factors. Toxicity, or auto-intoxication refers to the effect of the food that we consume has on cellular metabolism. This treatise is mostly concerned with the consequences of this latter process, and the measures we can take to detect, monitor and successfully manage such toxicity.

A dietary overload of too many concentrated and cooked foods that are lacking enzymes and nutrients can, in severe states lead to immune disorders such as candida albicans, allergies and lymphatic system toxicity from the absorption of incompletely digested macromolecules into the systemic circulation. Other immune system problems occur as protective barriers to potential pathogens are breached as a result of gastric hypoacidity and a diminution of “friendly” bacteria in the gut.

Gastric acid secretion can be measured by the Heidelberg gastric analysis test which measures pH of the digestive tract and determines the ability of the parietal cells to secrete hydrochloric acid. However, simple routine pH tests of anabolic urine and saliva after an acid and alkaline load or oral challenge test can yield accurate information regarding relative pH gradients of the digestive system.

Let me briefly discuss the definition of pH, and what it means in biochemical terms. pH, or the “potential of hydrogen” in water tells us how acid or alkaline a substance is. In water, the number of hydrogen ions present at any one time is equal to the number of hydroxyl ions, as the water molecule ionizes or splits into one of each. At 22ºC the concentration of hydrogen ions in water is 1 ion to 10 million water molecules (1 x 10-7). This is also true of hydroxyl ions. Multiplying the two figures together gives the constant for any solution (1 x 10-14). Adding an acid such as HCl (hydrochloric acid) to water will increase the number of hydroxyl ions present; adding an alkaline, or base, to water, such as NaOH (sodium hydroxide) will increase the number of hydroxyl ions. By referring to the constant above you will see that as the number of hydroxyl ions increase, so the concentration of hydrogen ions decreases to the point of total alkalinity (1 x 10-14).

The pH scale therefore runs from 0 to 14. Pure water has a pH of 7, is neither acid nor alkaline and represents the halfway point on this scale. Numbers below 7 are acidic, becoming more acid as the numbers approach zero. Numbers above 7 are alkaline, becoming more alkaline as they approach 14. But of course this scale is logarithmic, meaning a single number change in the scale (e.g. from 6 to 5 or from 7 to 8) is, in fact, a tenfold change in the acidity or alkalinity of a solution. A difference of 2 points on this scale means a hundredfold change in the pH chemistry of the solution. Since each point change on the pH scale represents such a large change in acidity or alkalinity, the scale is further divided into decimal points. For instance, the blood has a pH of 7.4 (range 7.35 to 7.45), making it slightly alkaline.

Acids and alkalis are highly reactive and will always tend to react to produce a neutral product. For example, HCl combines with NaOH to produce salt [NaCl] and water [H2O]; HCl also combines with calcium hydroxide [Ca(OH2)] to produce calcium chloride [CaCl2] and water.

How does this relate to body metabolism? Basically, if the body fluids are acid they will seek alkaline minerals to react with – such as sodium, potassium, zinc, iron, calcium. These are found in the liver, muscles, ligaments and bones, etc., if too little is available from the diet. But why should this happen? Effectively, all the body’s internal fluids are designed to be slightly alkaline, such as interstitial fluid, cerebrospinal and lymphatic fluid, liver bile and so on. The only exception to this is the hydrochloric acid produced by the stomach.

While our bodies are designed to be alkaline, cells produce acid as a by-product of their normal activity. The acid waste matter thus produced is reduced to carbon dioxide and water which are excreted harmlessly from the body.

When food is consumed and metabolised, however, not all of it is used up. A residue remains and this has been called ash (and perhaps the major area of disagreement in this subject is over the classification of foods into acid-ash forming and alkaline-ash forming foods). Digestion oxidises foods in much the same way as if they were burned except that it involves enzymes operating at low temperatures; a fruit will break down into carbohydrates that will further break down into carbon dioxide and water leaving a residual alkaline ash consisting of minerals salts such as sodium, potassium and calcium etc. So while a fruit will taste acid and present an acid pH if tested raw, its ash will be alkaline and so will its effect on the body. The small amount of protein in such foods will not change this.

Vegetables behave in the same way.

Proteins on the other hand leave an ash consisting of phosphates, sulphates and nitrates (from the phosphorus, sulphur and nitrogen that proteins contain). These are all acid. The net effect of protein consumption (whether from animal or vegetable sources) is to increase acidity.

The body has to rid itself of its acid wastes. This type of acid ash cannot be eliminated through the lungs as carbon dioxide and water in the same way as cellular metabolism. Instead the body has to buffer the ash with alkaline substances in order to neutralise it. Buffering takes place both inside and outside the cell, the majority of the buffering occurring in the blood itself. Each buffering system (bicarbonate, phosphate and protein) can shift the tissue pH to a maximum threshold (pK [constant] of bicarbonate buffer = 6.1; pK of phosphate buffer = 6.8; pK of protein buffer = 7.4). It is from these figures that we can begin to accumulate useful diagnostic data about the patients reactions to lifestyle and dietary stimuli using saliva and urine analysis.

Clinical research by Dr M T Morter (Arkansas, USA) has shown that if the anabolic urinary and salivary pH (measured immediately upon awakening) is below 6.8, we can be relatively certain that digestive support must be provided. Controlled clinical studies by Dr Paul Yanick (Pasadena, USA) have confirmed Dr Morter’s findings and recorded that intracellular assimilation of nutrients is significantly decreased when the anabolic pH is below 6.8

However as both these researchers have shown, supplementing the diet with appropriate alkalizing agents was highly beneficial in elevating the systemic pH by replenishing the alkaline mineral and enzyme reserves. Since systemic enzyme deficiencies show only in the last instance in the digestive tract, practitioners should not wait until the signs and symptoms of poor digestion become evident. From a preventative perspective, compensation should be made when symptoms are minimal and the anabolic pH is below 7.4 after an Alkaline Load Test (see “Correlative Urinalysis” by M T Morter).

At the age of 40, there is 15% less HCl in the stomach than at the age of 25, at the age of 65 there is but 15% present of the amount produced in the 25 year old. In the physiology of digestion in the stomach, the digestive hormone gastrin is released, stimulated by: [1] vagal nerve stimulation; [2] distension of the stomach by the presence of food, and, [3] the presence of partially digested proteins. Although gastrin stimulates the parietal cells to produce hydrochloric acid, parietal cells cannot perform their normal physiology when they are too toxic or when their intracellular pH is too low.

A reduction in gastric acid secretion by parietal cells that are too toxic causes disturbances in the integrated succession of enzyme reactions occurring in subsequent stages of digestion. Acid bile secreted by the gallbladder which has lost sodium due to the depletion of the alkaline reserve will commonly reverse the normal sequence of optimal pH ranges for efficient enzyme activity in the digestive process and interfere with the normal function of the ileo-caecal valve. Although the pancreas can form enough bicarbonate in order for the digestive enzymes to work in the small intestine, it is the gastric acidity that causes the hormone secretin to be released from the wall of the duodenum. Secretin in turn causes a copious secretion of pancreatic fluid and bicarbonate. Most pancreatic enzymes operate in a very narrow alkaline pH range, and unless and until the pH readings after an Alkaline Load are indicating normal digestive physiology, it will be necessary to use enzymatic digestive support. To ensure optimal absorption, the pH gradients of the digestive system must be corrected to the optimal range of enzyme activation, as described in physiology textbooks.

Diets which are high in protein, fat and simple carbohydrates and low in complex carbohydrates and raw food, stress the digestive mechanisms, inhibiting proper digestion and overloading the immune system with incompletely digested macromolecules and toxins. These digestive disturbances are aggravated by the typically high intake of food additives, pesticides and stimulating foods that are common in the Western diet.

It is essential in the digestion, assimilation and absorption of foods that there are sufficient enzymes, co-enzymes and organic minerals present in the gut to act as catalytic agents in the breakdown of food molecules, as well as in the assimilation of supplied nutrition.


Clinical Chemistry and Nutrition: A Physicians Desk Reference, Paul Yanick, Jr. PhD & Russell Jaffe, MD, PhD (T & H Publishing, Lake Ariel, PA)
Correlative Urinalysis, M T Morter, MS, DC (Best Research Inc., Rogers AR)
The Acid-Alkaline Solution to Total Health: Michael Sellar Dip, ION


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About Peter Bartlettt

Peter Barlett DO MCO MNTOS MCrOA is an Osteopath and Naturopath with clinics in London and Berkshire. He may be contacted on Tel: 0118 934 4203; Fax: 0118 934 4203;

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