This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Nearly all the great divisions of the vegetable kingdom afford wholesome food for man.
Vegetable food eaten in large quantity increases the elimination of carbon dioxide from the lungs. It also makes the urine alkaline and intensifies the alkalinity of other secretions. The urine of herbivorous animals is normally alkaline when they are well fed, but during prolonged fasting it becomes acid. The nursing calf when taking only animal food from the mother passes acid urine, but after weaning, when the animal changes to a vegetable diet, the reaction becomes alkaline.
The chief vegetable proteids are vegetable albumin, vegetable casein or legumin, and gluten. The latter predominates in the cerea-lia, and the legumin is principally found in pulses. These proteids are less rich in nitrogen than the corresponding animal albuminates.
Many vegetables contain tough cellulose, and at best not over 50 per cent of this material is digested and assimilated in man, although the lower animals derive much more nutriment from it.
A purely vegetable diet is not economical for a labouring man, for the reason that to derive sufficient nitrogenous substance from it he must either obtain the very best and most expensive cereals or legumes, or he must eat a very large quantity of vegetables. (See Vegetarianism, p. 35.) By the addition of albuminous food or fat to his diet he saves both expense and wear and tear of his digestive organs. If unable to obtain fresh meat, he may employ for this purpose milk, bacon, lard, dried fish, such as herring or cod. Among vegetable foods oatmeal and beans will furnish him with the largest available proportion of nitrogenous material. Vegetables, except those which are really seeds, such as those of the leguminosae or pulse tribe, contain but little fat.
A strict classification of vegetables is impossible in these pages. Green corn is certainly a vegetable, but it is more conveniently described in connection with cornmeal, samp, etc., among the cereals. (See Maize, p. 156).
Certain vegetables are classed as "green vegetables," meaning the lighter kinds of vegetables which contain considerable earthy salts and comparatively little starch, like spinach and lettuce, in distinction from heavy vegetables which contain much starch, like potatoes, beans, etc. The former term is used to describe fresh garden vegetables of all kinds in distinction from those which, like potatoes or onions, may be kept for some days or weeks without spoiling. The name is, however, too vague for accurate description.
"Greens" is the common name given to such vegetables as spinach, lettuce, beet tops, etc., which contain much chlorophyll and little starch or sugar, and which are eaten soon after being taken from the garden.
A simple division of vegetables for patients is (a) those the edible portions of which grow above ground and (b) those which grow below ground. With few exceptions, like the legumes, corn, and cabbage, the heavier vegetables - i. e., those which require more digestive power, and which contain abundant starch or sugar - grow below ground, or are tubers. Those which grow above ground are more digestible when fresh and young.
Celery, however, is not a tuber, is not especially "starchy," and yet grows, in part, at least, beneath the earth; so it is best in all important cases to specify by name the individual vegetables which can be partaken of rather than to describe them in general classes.
Many vegetables, in themselves difficult of digestion, may be made less so by conversion into well-cooked purees, or their extracts can be used for flavouring broths and soups for invalid use. Generally speaking, dried vegetables are much less digestible than when fresh. They become hard, stringy, and tasteless.
The following-named vegetables are those in common use which contain the largest percentage of both starches and sugars: Potatoes (both white and sweet), yams, beans, lentils, corn, peas, carrots, parsnips, beets, turnips.
Vegetable foods which are somewhat stimulant or pungent in their action are leeks, onions, garlic, herbs in general, mustard, cresses, mints, asparagus, and radishes. They increase the secretion of the saliva and gastric juice, and several are somewhat diuretic.
Some vegetables are laxative on account of their special chemical composition. Such, for example, are spinach, tomatoes, and most green vegetables when fresh and well cooked. Some, like cucumbers, are laxative from the seeds, or, like old corn, from the indigestible residue which they contain. The heavier vegetables, such as peas, beans, turnips, potatoes, etc., are liable to be constipating, although they aid normal peristalsis in that class of cases in which the diet has been previously mainly nitrogenous. (See Dietetic Treatment of Constipation).
Vegetables which have a special antiscorbutic reputation are cabbage, tomatoes, and all those used for fresh salads. These also furnish calcium oxalate in the urine.
All vegetables which are eaten raw should be thoroughly washed beforehand; otherwise they may be contaminated with manure and other impurities, or the excrement of domestic animals which have been roaming in the garden. The larvae of both tapeworms and roundworms have been transmitted to man in this manner. Water from foul wells is sometimes used for sprinkling gardens, and it is possible for typhoid, cholera, or other noxious germs to be spread by this means when the vegetables are eaten raw.