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Proteins require an acid medium for digestion. When animal proteins enter the stomach this stimulates the production of hydrochloric acid which activates the enzyme pepsin, whose function is the splitting and digesting of the proteins. This action in the stomach can only take place in a wholly acid medium; the presence of any concentrated starch or sugar with its accompanying alkalis interferes with, or neutralizes, this acid medium, and the proteins are then incompletely digested. The implications of this incomplete protein digestion are more serious than has hitherto been suspected. This is discussed in Chapter Three, in relation to allergy.

Carbohydrates (starches and sugars) require an alkaline medium for digestion. This is initiated in the mouth by the action of the enzyme, ptyalin, which splits the starches into lower forms before entrance into the small intestine where their further reduction and main digestion takes place. As the whole process of starch digestion depends on its proper initiation in the mouth, all starch foods must be thoroughly chewed, otherwise the small intestine, although alkaline in all its secretions, cannot complete what the ptyalin started higher up in the tract.

The stomach acts as a mixing chamber in which the saliva, with its active ptyalin, is thoroughly incorporated into the starches. During this early period in the stomach, lasting about 30 to 45 minutes, the normal acidity of the stomach is insufficient to cancel out, or interfere with, the alkaline medium necessary for preparing the starches for their intestinal digestion. The presence of meat, however, or other acid-compelling foods, or acid fruits, arrests this preparation and fermentation follows; the splitting-down process of starches can only occur in a positive alkalinity.

When asked what was the scientific basis for the theory that starches and sugars should not be eaten with proteins and acid fruits at the same meal, Dr Hay replied:

If starches are taken combined with acid fruits and if the stomach contents are withdrawn at intervals during digestion, it will be observed that the action of ptyalin has ceased and that the starches are not being split but will give the intense blue reaction of iodide of starch when iodine is applied to the chyme removed from the stomach. The same test may be performed with a combination of starches and proteins – the extraction of parts of chyme at intervals, as they happen during our digestion, will always show this arrest of ptyalin digestion meaning that the starches then unsplit will never be properly split.

For many years the teaching has been that the highest levels of acidity are in the resting stomach. This belief has been responsible for the advice given year after year, and still given to ulcer sufferers ‘to avoid letting the stomach get empty’. But a number of authorities disagree with this belief (now in disrepute in certain medical quarters), including the physiologist A.H. James. In Physiology of Gastric Digestion (Arnold, London, 1957) he states: ‘The highest acidities of all are reached during the digestion of food, not when the stomach is empty.’

This fact supports Dr Hay’s contention that if no protein accompanies a starch food entering a resting stomach the amount of hydrochloric acid is insufficient at first to fully neutralize or overcome the alkalinity of the saliva present.

In 1936, the work of three Philadelphia investigators provided interesting laboratory confirmation of the starch – protein concept. In Man Alive, You’re Half Dead! (Bartholomew House Inc., 1956), Dr Daniel Munro gives an account of a study on five subjects by these investigators showing the degree of acidity in the stomach after protein meals, after starch meals, and after combined protein and starch meals. This study revealed that, one-and-a-quarter hours after these meals were eaten, the stomach contents were most acid after the high-protein meal, least acid after the high-starch meal, and halfway between both states after the mixed meal. Moreover, when the mixed meal was eaten it was clear that the proteins were being digested under difficulties as the acidity present was far lower than that shown as required by the all-protein meal and had actually been cut to one-third less by the presence of the starches and their accompanying alkalis.

This investigation clearly shows that when high starches and high proteins are mixed at one meal there is too much acid to permit the continued alkaline reduction of the starch part, and not enough acid to start the digestion of the protein part.

The usual teaching, however, is that when we eat food of any kind (such as proteins and starches) we produce gastric juice which contains hydrochloric acid. The answer, here, is that hydrochloric acid is stimulated in exact ratio to the amount of protein presented by the digestive task. This was shown by Pavlov’s classic observations on dogs in The Work of the Digestive Glands (Charles Griffin & Co. Ltd, 1910).

As already pointed out, the protein in starches such as grains is both very small (about 10 per cent) and incomplete in character, and therefore does not stimulate sufficient hydrochloric acid to interfere, for the first 30 to 45 minutes, with the alkaline medium necessary for the digestion of starches. During this time, the saliva – which has a pH value of 6.6, as compared with the pH 0.9 of pure gastric juice – acts as a natural buffer of the gastric acid.

Some physiologists and physicians disagree with Dr Hay’s explanation of the starch – protein theory and claim that the gastric acid is necessary for the splitting of the starches; the starch is often contained in protein ‘envelopes’ which require the acid for digestion so that the starch can be released. This claim is undoubtedly correct but it does not alter the fact that starches have a preliminary digestion in an alkaline medium which buffers the gastric acid for the first 30 to 40 minutes in the stomach. There is, therefore, still plenty of time for the gastric acid to work on the starches during the remaining three or more hours that they are in the stomach before entering the small intestine. There, of course, the pancreatic juice completes the digestion of carbohydrate (starch, dextrin and the like), and also of protein, in a mainly alkaline medium.

Whether Dr Hay’s explanation of his theory is right or wrong, however, does not really matter; the indisputable fact remains that his theory does most certainly work. As he pointed out, any professor of medicine who claims that it does not has never given it a fair trial, otherwise he could not with honesty make such a claim.