( Originally Published 1913 )
White and Sweet Potatoes, Manioc, Sago, Tapioca, and their Advantages.
Just as is the case with bread, many people feel that they cannot do without potatoes. Especially in the northern regions, as in Scandinavia, and even more so in Ireland, does the potato form a chief part of the daily food. In many sections of northern Hungary the Slovaks live almost exclusively upon potatoes. In my country, too, there are large numbers of people from whose tables they are never absent; this great liking for them, which seems to be almost instinctive, is readily understood, for in this region potatoes, together with bread, supply our daily needs of carbohydrate materials, of which potatoes contain 16 to 22 per cent. They also constitute—particularly new potatoes—a very agreeable food, especially when well prepared. The taste-bearing constituents in them disappear very rapidly, so that when they are pared and placed in water they soon lose their taste, especially when the water is heated. Far this reason potatoes should always be boiled in the skins; the best way is to put them into boiling water and let them cook for about half an hour, until they are quite soft. When the potatoes are sufficiently cooked, they should be peeled and served at once, for their taste is rapidly lost. Whoever is fond of potatoes should not come late to meals in a hotel, but should endeavor to be among the first, for when peeled and prepared some time before, they no longer taste very good; even the delicious new potatoes get hard. The digestibility of the potato, also depends upon the manner of its preparation, for we must remember that the digestible nourishing portions, the starch granules, are imbedded in a covering of cellulose. These shells may be expected to burst open in the cooking, so that the digestive juices can act upon the nutritious substances within. When potatoes have been thoroughly cooked and are served mashed in the form of a purée, they give the stomach but little work, and can be well assimilated in the intestine, for the cellulose can then do no harm. The case is very different, however, when potatoes are sliced and fried, and perhaps only partially cooked through. They then seem tender on the outside, but the cellulose in the interior portions has not been rent asunder; the starchy portions remain in a raw condition, and, as Strassburger has shown, appear undigested in the feces. When potatoes are taken in the form of a salad, about i per cent. of the carbohydrate constituents is lost, according to Rubner. The most healthful way, therefore, is to eat potatoes in the form of a purée. Good, dry, mealy potatoes, when steamed, sliced and browned, are well tolerated and assimilated. Whole roasted potatoes are in-digestible, badly assimilated, and often give rise to acid eructations; they are consequently not adapted for stomach and intestinal troubles.
The taste of potatoes and the amount of starch contained in them depend upon the climate and soil. In some countries, in England and Holland particularly, they grow very well and have a very excellent taste. The starch content is dependent upon the sun they receive, as is the case with tubers in general, for through the influence of the sun's rays the starch, which is formed in the leaves, is stored up. The tubers in these plants may be said to occupy about the same position in their makeup as does the liver with us, since the starch is also deposited in this organ, to be converted into sugar as required and then consumed. After a summer in which there has been plenty of sunny weather, the potatoes show an unusually high starch content. Generally the amount ranges from 16 per cent. in the young potatoes to 22 per cent. in the old ones ; the older the tuber, the more starch has been deposited in it. Of the other nutritive substances, e.g., albumin, the potato contains but little, the minimal amount being o.69 per cent. and the maximum 3.67 per cent. ; of fat there is even less,-O.04 to 0.96 per cent.
The potato not only contains very little albumin, but only about one-half of this is digestible; the rest occurs in the form of amino-compounds,--for the most part asparagin,—which may probably also play some useful rôle.
Since potatoes contain so little fat, it is advisable not to eat them alone, but to add butter. Dry potatoes certainly do not taste good, but fresh potatoes with good butter, or potatoes browned in butter, with a crisp, appetizing crust, as they are so deliciously prepared in Paris, and occasionally in England, are most palatable. As potatoes are poor in albumin, and meat, on the other hand, is poor in carbohydrates, these two articles of food should go hand in hand, as it were; a roast of meat does not seem complete without potatoes, nor do the potatoes without meat. To be sure, good potatoes carefully fried are by no means to be despised as a food when eaten alone, but in a vegetable diet they do not play the same rôle as for the meat-eater, since the vegetarians can better obtain their required amounts of carbohydrate from rice, sago, tapioca, etc. These contain a much greater total of carbohydrate material and are consequently more nutritious for the vegetarian, while potatoes are more voluminous and less nutritious. According to Bunge, potatoes also give rise to a craving for salt, owing to the large amount of potash and the slight quantity of soda contained in them, as a consequence of which more common salt is excreted and must be again replaced.
The diet of the vegetarian is, in general, already poor in salt, so that he should not add to it large amounts of any article of food which will increase the desire for salt further. Rice is, therefore, far preferable for him. The potash content is greater than that of, perhaps, any other food, amounting to, 60 per cent. We shall now describe the mineral contents of the potato, as given by König.
As to the content of phosphorus, one of the most important of the mineral substances in our food, potatoes when cooked contain, according to Jebbink, 0.10 per cent. of phosphoric acid ; according to Balland, o.01 per cent. of phosphorus and o.22 per cent. of phosphoric acid. In the table of Schall and Heisler 160 milligrams of phosphoric acid are given as being contained in 100 grams of the fresh substance.
When we wish to introduce many alkaline substances into the body, potatoes render good service; large quantities will render the urine alkaline. Mossé states that in 1 kilo of potatoes there is contained almost as much of alkaline substance as is present in 1 liter of Vichy water, and he has also observed—as is often the case after the use of alkaline waters—that the sugar in the urine of his diabetic patients was considerably decreased after potatoes had been eaten, for which reason he recommends a diet exclusively of potatoes in the treatment of diabetes. The sugar really does often disappear after such treatment, but, as I have stated in my work on new methods and measures of treatment in diabetes, we possess more rational modes of treating this disease than such an impracticable and purposeless diet, in which the lack of albumin in the food would surely also exert a therapeutic influence upon the diabetes. In addition to the potash content the asparagin no doubt also plays a rôle. Stocklasa and Biernacki have shown that a large content of potash in the food greatly favors the breaking down of carbohydrates.
It would be a great mistake to allow all diabetics to take potatoes; I have myself seen injurious effects follow reckless use of this food in diabetes. As soon as meat is given together with the potatoes, the elimination of sugar is readily increased. It would be best to use the potatoes in small quantities, fried or, better still, in the form of salad, since they are then not so well assimilated. In obesity potatoes should not be allowed, since the fat may be increased owing to their carbohydrate content. In kidney diseases the increased amount of salt taken with the potatoes might come into play. They also contain purin bases—uric acid producers—according to Bessau and Schmidt, to the extent of 0.002; this is really but a small amount, so that potatoes need not be strictly forbidden in gout. Their tendency to produce flatulence should be given due weight in gout as well as in arteriosclerosis. If, however, the potatoes are taken in the form of a purée, instead of fried or roasted, flatulence may be avoided. The question must be well considered before such a much-used and well-liked food as the potato is absolutely forbidden.
In the tropics and in the United States, a kind of sweet potato is frequently eaten. I found the taste of sweet potatoes very agreeable, something like a chestnut purée, and often ate them fried, and liked them very much. I found them some-what indigestible, however, somewhat less so when boiled, but am inclined to think that they are more apt to cause acidity of the stomach than our native potatoes. It would be well to cultivate this useful variety of potato in our country.
In countries where the sun is almost always shining, thus causing great heat, a great quantity of starch is formed in the tuberous roots of certain trees, as in the "manihot" tree, called the cassava tree in South America and Java, which belongs to the Euphorbiaceæ. When the knots on the roots of these trees, which are often very large, are cut open, a white, starch-like mass will be seen to fill the cavity. After having been very carefully cleaned, for the removal of a poisonous substance, this starchy mass is then spread out on a hot metallic plate. From the manioc, and also from the starch obtained from the roots of a tree belonging to the Marantacea, the Maranta arundinacea (arrowroot), as well as from the Colocaria Taro in Africa and Tahiti, the Curcurmartes, various starch-containing substances like tapioca are made. The trunks of palm trees contain a great deal of starchy flour, and from it sago is made, which consists of little granules. Tapioca and sago are also made in Europe from the starch obtained from potatoes. These foods present many advantages. In the first place they are nutritious, since they contain 78 to 88 per cent. of carbohydrates, in such a form that it is scarcely equaled by any other food in regard to the assimilation of the starches; they are almost entirely free from cellulose, and therefore the intestinal juices can act fully upon them. They are consequently very easily digested both by the stomach and intestines, and do not impose much work upon the stomach, although they remain in it for some time, as the gastric juices do not digest the carbohydrates, which are digested by the saliva and intestinal juice. In cases of intestinal disturbances the best among the carbohydrate foods would no doubt be sago or tapioca; they would be less desirable in overacidity of the stomach. Since they are rather tasteless, and are not rich in albumin (o.30 to 1.13 per cent.), it would be desirable to mix them with milk or make puddings of them with eggs and milk or cream. Such a pudding is most easily digested. It might be stated, in reference to their action upon the intestines, that these starchy foods, owing to their content of sugar, have the property of causing a lactic acid fermentation in the intestine, which, so to speak, disinfects it, and has a beneficial effect upon the entire organ-ism. In kidney affections they are a most excellent food, since they contain absolutely nothing which might prove injurious to the kidneys ; the same may be said of the blood-vessels ; so they are a good dietetic food in arteriosclerosis, as well as in gout, since they do not form any uric acid, being entirely free from substances which produce it. For delicate persons, these foods are ideal, but they are not well adapted for strong, healthy men, for whom a carbohydrate food which requires some chewing, like hard black bread, or one containing cellulose in a sufficient quantity to act upon the intestine, would be preferable. Foods like sago, etc.,—rich in carbohydrates and very easily assimilated,—should play an important part in a vegetarian diet, in which the cellulose is well represented, but the easily digested forms of carbohydrates less so,. In this connection, tapioca and sago, corn and other fine, starchy flour, would be ideal. That these foods would be poison, so to speak, for diabetics is clear. The sugar contained in them is absorbed in large quantities at a time, and the organism is flooded with it; it is therefore preferable for such patients, when they re-quire the carbohydrates, to take them in foods containing much cellulose, so that the sugar be only gradually absorbed, and the sugar-destroying agents in the body have time to convert it into an eliminable product. When we forbid the use of these foods in obesity and advise those rich in cellulose, we are actuated by similar motives.