Experiments on a somewhat extended scale have shown within recent years that young and vigorous individuals at least may live and thrive on a diet composed largely of vegetables; no one has yet shown that a strict vegetable diet is that best adapted to the average individual, and no competent authority on this subject at the present time advocates a diet purely of this kind. It is true that the vegetables ordinarily eaten contain all of the elements that are essential to the animal system, such as starch, sugar, fat and albumins. Unfortunately, however, the amount of the last-named substance is usually so small in food-plants that the quantity that would have to be eaten by a normal individual taking active exercise would cost considerably more than if a reasonable proportion of animal food were included, and—which is of even greater importance—the digestive powers of the individual who attempted to live only on food of this character would be severely taxed, and, in the long run, probably seriously impaired. Furthermore, vegetables and fruits contain substances, usually in great quantity, that are scarcely acted upon at all by the digestive juices. Chief among the latter is cellulose, which, while forming the great bulk of the food of herbivorous animals, is scarcely suited to the weaker digestive capacity of the human being; practically none of it is converted to the uses of the body. It is thus seen that in the average man or woman a dietary consisting largely of vegetables would result in the presence in the intestines of a greater or less bulk of indigestible materials, which could subserve no good purpose other than that they would by their mechanical presence have a tendency to cause the bowels to act; as is the case with fruits, however, it is unfortunately true that this large residue of undigested food, in one way or another, often gives rise to considerable irritation of the mucous membrane of the intestine, and frequently produces dyspeptic disturbances, among which looseness of the bowels is common.
This brings us to a consideration of the digestibility of vegetables in general, which is always the paramount consideration when dealing with the value of any substance to be used as a food. It has been before remarked that young and vigorous persons seem to thrive on a dietary largely of vegetable character, but the case is certainly quite different with older people, particularly where their digestive powers are impaired. In the latter we often find that severe intestinal disturbances follow even after moderate indulgence in vegetable foods—particularly where they are served with vinegar, or some other fruit acid. Another peculiarity of foods of this kind that makes decidedly against their digestibility lies in the fact that, being soft and containing a large proportion of water, they are scarcely ever properly chewed, and as a consequence they are swallowed in comparatively large masses without having been adequately insalivated.
Vegetables may be roughly classified as legumes, roots and tubers, and green vegetables, and will now be considered briefly in the order named.
Legumes,—Beans, Peas, Lentils, and Peanuts.—With the exception of the cereals, the legumes are the most valuable of all vegetable foods. Their nutritious properties are mainly due to their relatively high percentage of nitrogenous material, though they also contain starch and fat. Hence these vegetables contain the ingredients necessary to supply all the needs of the human economy; unfortunately, however, when eaten alone in sufficient bulk to furnish the nourishment required, they often—even in healthy individuals—give rise after a little time to dyspeptic disturbances.
Of beans, a large number of different varieties are in common use including string-beans (or snap-beans), lima-beans, kidney-beans, red beans, the frijole, and the Soya bean. String-beans are exceedingly palatable, and are very much prized as an article of diet by the peoples of all countries. When gathered young and thoroughly cooked while still fresh they are exceedingly wholesome, and are very well assimilated, when properly chewed, by even those whose digestions are considerably impaired. The other beans named are generally eaten dry after having been removed from the pod in which they grow. When they are soaked in water until they become soft and then thoroughly cooked they make an excellent food, and, when not taken in too great quantities, are fairly digestible. When cooked with onions, parsley, and red pepper in proper proportions they make a very delicious dish. In Japan the Soya bean forms the basis for a kind of vegetable cheese which is eaten with rice, and furnishes the nitrogenous materials in which the latter is deficient. Peas are wholesome when young and fresh and when properly cooked, and as they come on in the early spring when other fresh vegetables cannot be obtained, they furnish a most acceptable addition to the dietary. When old, after their skins become tough, they cease to be digestible, and should not be eaten except in the form of purees, during the preparation of which the hull is removed.
Lentils are scarcely eaten at all in America, but are much prized in some portions of the Old World, as the basis of soups.
Peanuts belong to the group of legumes, though, unlike the others that serve as food, they grow beneath the surface of the ground. They are highly nutritious, but are, unfortunately, indigestible, owing largely to the high percentage of oil that they contain. The latter is extracted, and is sometimes sold as olive-oil; in a somewhat different form it is made into a sort of butter which is quite palatable.
Roots, Tubers, and Yams.—Sweet and Irish potatoes, which constitute the most important members of this group, have already been discussed under the head of breads. Of those that remain, some few, as beets and artichokes, may be regarded as related to those just referred to, while others, such as carrots, turnips, radishes, parsnips, etc., are generally reckoned among the succulent tubers on account of the large proportion of juice that they contain. Irrespective of the beet, which furnishes a considerable portion of the sugar of commerce, none of them may be looked upon as foods of a very important character, as they contain only relatively small proportions of sugars, starches, and nitrogenous materials. Beets, however, do contain a very high percentage of that which makes potatoes so popular,—about eighty-five per cent. of starches and sugars, with only a trifle of nitrogenous material. When young and tender they are often eaten as a salad, either alone or mixed with other vegetables, and are generally regarded as being wholesome and highly nutritious. They should not be eaten by dyspeptics when pickled, on account of the vinegar.
Artichokes are occasionally eaten, but are not nutritious, although they agree well with many persons.
Carrots, when young and fresh, are fairly digestible, but like other vegetables are exceedingly apt, particularly if old, to produce intestinal disturbances in dyspeptics. They are not very commonly eaten in the United States, but where selected with care we would profit by their more frequent use. They contain a small percentage of starches, with an insignificant proportion of vegetable albumin.