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Popular Science Monthly/Volume 29/May 1886/Food Accessories and Digestion

< Popular Science Monthly‎ | Volume 29‎ | May 1886


MAN, like any other animal, is so much the creature of his food—his physical perfection, his intellectual activity, and his moral tone are so dependent on the food he receives and the uses he is able to make of it in the processes of digestion and assimilation—that any accurate knowledge, founded on precise and reliable methods of investigation, of the influence on digestion and nutrition of dietetic habits must of necessity be of the most general interest.

To Professor Sir William Roberts, of Manchester, we were already greatly indebted for a series of able and comprehensive researches on the action of "digestive ferments" and the "preparation and use of artificially digested food";[1] to those valuable researches Sir W. Roberts has recently added others equally important, chiefly on the subject of "food accessories" and their influence on the chemical acts of digestion.[2]

The results of these experimental inquiries are, in some respects, so novel and unexpected, and they contradict so many apparently unfounded assumptions, that they can not be too soon or too widely known.

Man, as Sir W. Roberts begins by pointing out, is a very complex feeder; he has departed, in the course of his civilization, very widely from the monotonous uniformity of diet observed in animals in the wild state. Not only does he differ from other animals in cooking his food, but he adds to his food a greater or less number of condiments for the purpose of increasing its flavor and attractiveness; but, above and beyond this, the complexity of his food-habits is greatly increased by the custom of partaking in considerable quantity of certain stimulants and restoratives, which have become essential to his social comfort if not to his physical well-being.

The chief of these are tea, coffee, cocoa, and the various kinds of alcoholic beverages.

It is to these "food accessories" and the elucidation of their influences on the processes of digestion that Sir TV. Roberts's recent experiments and observations have been directed.

These "generalized food-customs of mankind," he remarks,

are not to be viewed as random practices adopted to please the palate or gratify our idle or vicious appetite. These customs must be regarded as the outcome of profound instincts, which correspond to important wants of the human economy. They are the fruit of colossal experience, accumulated by countless millions of men through successive generations. They have the same weight and significance as other kindred facts of natural history, and are fitted to yield to observation and study lessons of the highest scientific and practical value.

It is unnecessary to describe here Sir W. Roberts's methods of investigation; they are fully set forth in the volume before us, and they are alike admirable for the ingenuity of their conception and the laborious accuracy of their prosecution.

His object was to ascertain the precise influence of these food accessories on the three chief parts of the digestive process: 1. Salivary digestion, i. e., the action of the saliva as a digestive agent; 2. Peptic digestion, i. e., the action of the fluids secreted by the stomach as digestive agents; and, 3. Pancreatic digestion, i. e., the action of the secretion of the pancreas as a digestive agent.

We shall deviate a little from Sir W. Roberts's method of marshaling his conclusions, and shall summarize his results as to the action of the various food accessories on these three acts of digestion continuously.

First, with respect to the action of ardent spirits on digestion. The experiments were made with "proof-spirit" and with brandy, Scotch whisky, and gin; and the conclusion is that, so far as salivary digestion is concerned, these spirits, when used in moderation and well diluted, as they usually are when employed dietetically, rather promote than retard this part of the digestive process, and this they do by causing an increased flow of saliva. "A teaspoonful of brandy or whisky introduced into the mouth can be perceived at once to cause a gush of saliva. The common practice of adding a tablespoonful of brandy to a basin of arrowroot or sago gruel, therefore, promotes its digestion."

The proportion must not, however, much exceed five per cent, and gin seems to be a preferable addition to either brandy or whisky. It was noticed in these experiments that brandy and Scotch whisky interfered with the digestive process, "precipitated the starch more readily," altogether out of proportion to the amount of alcohol they contained, and brandy was worse than whisky; and this circumstance appears to be due to certain ethers and volatile oils in them; and brandy contains a trace of tannin, which has an intensely retarding influence on salivary digestion.

With regard to "peptic" digestion the results are still more surprising. It was found that with ten per cent and under of proof-spirit there was no appreciable retardation, and only a slight retardation with twenty per cent; but with large percentages it was very different, and with fifty per cent the digestive ferment was almost paralyzed.

In the proportions in which these spirits are usually employed dietetically not only do they not appreciably retard digestion, but these experiments show that they "act as pure stimulants to gastric digestion, causing an increased flow of gastric juice and stimulating the muscular contractions of the stomach, and so accelerating the speed of the digestive process in the stomach." For obvious reasons (stated in these lectures) alcoholic drinks as used dietetically can never interfere with pancreatic digestion.

Passing from the consideration of the influence of these ardent spirits on digestion to the more complex problem of the influence of such alcoholic beverages as the various wines and malt liquors, Sir W. Roberts arrives at the following conclusions:

Even very small quantities of the stronger and lighter wines—sherry, hock, claret, and port—exercise a powerful retarding influence on salivary digestion. This is wholly due to the acid—not the alcohol—they contain, and if this acid be neutralized, as it often is in practice, by mixing with the wine some effervescent alkaline water, this disturbing effect on salivary digestion is completely removed.

The influence of acids in retarding or arresting salivary digestion is further of importance in the dietetic use of pickles, vinegar, salads, and acid fruits.

In the case of vinegar it was found that 1 part in 5,000 sensibly retarded this process, a proportion of 1 in 1,000 rendered it very slow, and 1 in 500 arrested it completely; so that when acid salads are taken together with bread the effect of the acid is to prevent any salivary digestion of the bread, a matter of little moment to a person with a vigorous digestion, but to a feeble dyspeptic one of some importance.

There is a very wide-spread belief that drinking vinegar is an efficacious means of avoiding getting fat, and this popular belief would appear from these experimental observations to be well-founded. If the vinegar be taken at the same time as farinaceous food, it will greatly interfere with its digestion and assimilation.

As to malt liquors, provided they are sound and free from acidity, they interfere but little with salivary digestion; if they are acid, it is otherwise.

Effervescent table-waters, if they consist simply of pure water charged with carbonic acid, exercise a considerable retarding influence on salivary digestion; but if they also contain alkaline carbonates, as most of the table-waters of commerce do, the presence of the alkali quite removes this retarding effect.

"The use of these waters as an addition to wines is," Sir William Roberts observes, "highly commendable," as they "greatly mitigate or wholly obviate the retarding influence of these wines on the digestion of starch."

It was also observed that these weaker forms of alcoholic drinks (wines and beer) differed greatly in their influence on peptic digestion to that of the distilled spirits. They retarded it altogether out of proportion to the quantity of alcohol they contained. Port and sherry exercised a great retarding effect. "Even in the proportion of twenty per cent sherry trebled the time in which digestion was completed." It should further be borne in mind that this wine also greatly retards salivary digestion. Sherry, then, is not a suitable wine for persons of feeble digestive powers.

With hock, claret, and champagne it was also ascertained that their retarding effect on digestion was out of proportion to the alcohol contained in them; but champagne was found to have "a markedly less retarding effect than hock and claret"; indeed, in the proportion of ten per cent champagne had a distinct, though slight, accelerating effect, and this superiority of champagne appears to be due to the "mechanical effects of its effervescent qualities."

The quantity of claret and hock often consumed by many persons at meals must exercise a considerable retarding effect on peptic digestion; but small quantities of these wines (and even of sherry) do not produce any appreciable retarding effect, but act as pure stimulants. These wines, then, may be taken with advantage, even by persons of feeble digestion, in small quantities, but not in large.

With regard to malt liquors, it was observed, as with wines, that they retarded peptic digestion in a degree altogether out of proportion to the amount of alcohol contained in them, and when taken in large quantities they must greatly retard the digestion, especially of farinaceous food; but a moderate quantity of light beer, when "well up," is favorable to stomach digestion.

It was proved by these experiments that the sparkling wines impede digestion less than the still ones, and when taken in moderate quantity "act not only as stimulants to the secretion of gastric juice and to the muscular activity of the viscus, but may, at the same time, slightly accelerate the speed of the chemical process in the stomach."

Next as to the influence of tea, coffee, and cocoa on the digestive processes:

Tea exerts a powerful retarding influence on salivary digestion, coffee and cocoa a comparatively feeble one.

Sir W. Roberts estimates the medium strength of the tea usually drunk at four to five per cent; strong tea may contain as much as seven per cent, weak tea as little as two per cent. Medium coffee has a strength of about seven per cent, and strong coffee twelve to fifteen per cent; cocoa, on the other hand, is generally weaker, not more than about two per cent, and this, he thinks, may be one reason why it is more suitable to persons with feeble digestions than tea or coffee.

Tea exercises a powerful inhibitory effect on salivary digestion, and this appears to be entirely due to the large quantity of tannin it contains.

It appears that tannin exists in two conditions in the tea-leaf. One, the larger portion, is in the free state, and is easily extracted by hot water; but about one fourth is fixed and remains undissolved in the fully exhausted tea-leaves. Some persons have supposed that by infusing tea for a very short time only two or three minutes—the passing of tannin into the infusion would be avoided. This is a delusion; you can no more have tea without tannin than you can have wine without alcohol. Tannin, in the free state, is one of the most soluble substances known. If you pour hot water on a little heap of tannin it dissolves like so much pounded sugar. Tea infused for two minutes was not found sensibly inferior in its retarding power on salivary digestion to tea infused for thirty minutes.

One gentleman of my acquaintance (says Sir W. Roberts) in his horror of tannin was in the habit of preparing his tea by placing the dry leaves on a paper filter and simply pouring on the boiling water. In this way he thought to evade the presence of tannin in his tea. But if you try the experiment, and allow the product, as it runs through the filter, to fall into a solution of perchloride of iron, you will find that an intense inky-black coloration is produced, showing that tannin has come through in abundance.


In order to diminish as far as possible the retarding influence of tea on salivary digestion, it should be made weak and used sparingly, and it should not be taken with but after the meal.

There is another means, mentioned by Sir W. Roberts, of obviating the retarding effect of tea on salivary digestion, and commended by him to the dyspeptic: it is to add a pinch of bicarbonate of soda to the tea when it is being infused in the tea-pot. He found that ten grains of soda added to an ounce of dry tea almost entirely removed this retarding influence. The infusion thus made is darker than usual, but the flavor is not sensibly altered, nor is the infusion rendered alkaline, for tea infusion is naturally slightly acid, and the soda, in the proportion mentioned, only just neutralizes this acidity.

Coffee, unless taken in very large quantity, has very little retarding effect on salivary digestion; this is explained by the fact that the tannin of tea is replaced in coffee by a substance called caffeo-tannic acid. Cocoa resembles coffee, and has little or no effect on salivary digestion; the use of coffee or cocoa is therefore preferable to that of tea for persons of feeble digestion.

With respect to the influence of tea and coffee on stomach digestion, it was found that they both exercised a remarkable retarding effect. There was no appreciable difference in the two beverages if they were of equal strength; but, as coffee is usually made of greater percentage strength than tea, its effect must ordinarily be greater. Cocoa also had much the same effect if used of the same strength as tea or coffee, but, when of the strength ordinarily employed, its effect was inconsiderable. Strong coffee cafe noir had a very powerful retarding effect, and persons of weak digestion should avoid the customary cup of "black coffee" after dinner.

"I could not detect," says Sir W. Roberts, "any appreciable difference between the effect of tea infused for two or three minutes and tea infused for fifteen or thirty minutes. If you wish to minimize the retarding effects of tea in persons of weak digestion, you should give instructions that the beverage be made weak, or that it be used in sparing quantities." And he adds in a footnote: "A good deal has been said of the injurious effects on gastric digestion of tannin contained in tea. I question whether the statements made with reference to this matter are worthy of attention. It has been alleged that meat-fiber is hardened by tea, and that the coats of the stomach are liable to be injured by this beverage. These views are entirely theoretical" (p. 48).

Perhaps one of the most unexpected results of these experiments of Sir W. Roberts was the discovery that beef-tea had a powerful retarding effect on peptic digestion, as much so as that of a five per cent infusion of tea. Further researches appeared to show that this retarding effect of beef-tea was due to the salts of the organic acids contained in it.

While on the subject of beef-tea, it will be novel and instructive to many to hear that

there is a wide-spread misapprehension among the public in regard to the nutritive value of beef-tea. The notion prevails that the nourishing qualities of the meat pass into the decoction, and that the dry, hard remnant of meat-fiber which remains undissolved is exhausted of its nutritive properties; and this latter is often thrown a way as useless. A deplorable amount of waste arises from the prevalence of this erroneous notion. The proteid matter of meat is quite insoluble in boiling water, or in water heated above 160° Fahr. The ingredients that pass into solution are the sapid extractives and salines of the meat, and nothing more except some trifling amount of gelatine. The meat remnant, on the other hand, contains the real nutriment of the meat, and if this be beaten to a paste with a spoon or pounded in a mortar and duly flavored with salt and other condiments, it constitutes not only a highly nourishing and agreeable but also an exceedingly digestible form of food.[3]

Beef-tea must therefore be looked upon rather as a stimulant and restorative than as a nutrient beverage, but it is nevertheless very valuable on account of those properties.

Sir W. Roberts puts forward an ingenious argument, which can not be fully repeated here, in favor of the view that, in healthy and strong persons, this retarding effect on digestion observed to be produced by many of the most commonly consumed food accessories answers a distinctly useful end. They serve, he maintains, the purpose of wholesomely slowing the otherwise too rapid digestion and absorption of copious meals.

A too rapid digestion and absorption of food may be compared to feeding a fire with straw instead of with slower-burning coal. In the former case it would be necessary to feed often and often, and the process would be wasteful of the fuel; for the short-lived blaze would carry most of the heat up the chimney. To burn fuel economically, and to utilize the heat to the utmost, the fire must be damped down, so as to insure slow as well as complete combustion. So with human digestion: our highly prepared and highly cooked food requires, in the healthy and vigorous, that the digestive fires should be damped down, in order to insure the economical use of food. . . . We render food by preparation as capable as possible of being completely exhausted of its nutrient properties; and, on the other hand, to prevent this nutrient matter from being wastefully hurried through the body, we make use of agents which abate the speed of digestion.

It must be borne in mind that these remarks apply only to those who possess a healthy and active digestion. To the feeble and dyspeptic any food accessory which adds to the labor and prolongs the time of digestion must be prejudicial; and it is a matter of common experience that beverages which in quantity retard digestion have to be avoided altogether by such persons or partaken of very sparingly.

In the dietetic use of wines the writer of this article has constantly had occasion to make the observation that those wines agree best and are most useful which are absorbed and eliminated from the system with the greatest rapidity, as tested by the increase of the renal secretions, and he has been led to the practical conclusion that this is the best criterion of the suitability of any particular wine to any particular constitution. If the effect of different wines on notoriously gouty persons be carefully observed, it will be found that some can drink champagne (in moderation, of course) with impunity, especially if a small quantity of an effervescing alkaline water be added to it, while claret will at once provoke some manifestations of gout; others, who are unable to drink champagne without provoking a gouty paroxysm, will often be able to drink a mature, fine, soft claret even with advantage; others will support hock well, and a few can drink fine sherries and ports in small quantities; but in all it will be found that the test of the suitability of the particular wine to the particular constitution is its susceptibility to rapid elimination and vice versa.

It has occurred also to the writer to make many observations as to the circumstances under which tea and coffee are found to agree or disagree with different persons; in the first place, as Sir W. Roberts has pointed out, tea, if taken at the same time as farinaceous food, is much more likely to retard its digestion and cause dyspepsia than if taken a little time after eating; and the custom adopted by many persons at breakfast, for instance, of eating first and drinking their tea or coffee afterward is a sensible one; so also it is better to take one's five-o'clock tea without the customary bread-and-butter or cake than with it.

Indeed, while there is little that can be said against a cup of hot tea as a stimulant and restorative, when taken about midway between lunch and dinner, and without solid food, it may, on the other hand, be a fruitful cause of dyspepsia when accompanied at that time with solid food. It is also a curious fact that many persons with whom tea, under ordinary circumstances, will agree exceedingly well, will become the subjects of a tea dyspepsia if they drink this beverage at a time when they may be suffering from mental worry or emotional disturbance.

Moreover, it is a well-recognized fact that persons who are prone to nervous excitement of the circulation and palpitations of the heart have these symptoms greatly aggravated if they persist in the use of tea or coffee as a beverage. The excessive consumption of tea among the women of the poorer classes is the cause of much of the so-called "heart-complaints" among them: the food of those poor women consists largely of starchy substances (bread-and-butter chiefly), together with tea, i. e., a food accessory which is one of the greatest of all retarders of the digestion of starchy food.

The effect of coffee as a retarder of stomach digestion would probably be more felt than it is were it not so constantly the practice to take it only in small quantity after a very large meal; it is then mixed with an immense bulk of food, and its relative percentage proportion rendered insignificant; and to the strong and vigorous the slightly retarding effect on digestion it would then have may be, as Sir W. Roberts suggests, not altogether a disadvantage; but after a spare meal and in persons of feeble digestive power the cup of black coffee would probably exercise a retarding effect on digestion which might prove harmful. It is also worthy of remark that in the great coffee-drinking countries this beverage is made not nearly so strong as with us. In this country good coffee always means strong, often very strong coffee; but on the Continent they possess the faculty of making good coffee which is not necessarily very strong coffee, and which is, therefore, as a beverage, less likely to do harm.

The general conclusion to be drawn from these highly interesting and instructive researches is that most of the "food accessories" which in the course of civilization man has added to his diet are, when taken in moderation, beneficial to him, and conduce to his physical welfare and material happiness; but if taken in excess they may interfere to a serious and harmful degree with the processes of digestion and assimilation. It is also made clear that dietetic habits which may prove agreeable and useful to those who enjoy vigorous health and a strong digestion need to be greatly modified in the case of those who are feeble and dyspeptic.—Nineteenth Century.


  1. " On the Digestive Ferments and the Preparation and Use of Artificially Digested Food." Lumleian Lectures, delivered before the Royal College of Physicians in 1880 by Sir William Roberts, M. D., F. R. S. London: Smith, Elder, & Co.
  2. "Lectures on Dietetics and Dyspepsia." Smith, Elder, & Co.
  3. "These remarks on beef-tea apply equally to Liebig's extract of meat, Brand's essence of beef, and Valentine's me at-juice, all of which are devoid of albuminous constituents" ("British Medical Journal," August, 1885).