CLASSIFICATION OF FOODS
In the previous chapters, we have given the classification of the elements in foods which supply the body needs. Below we classify the foods commonly used, according to the predominance of these elements.
Carbonaceous Foods
While all foods contain a combination of elements, the foods described below contain a greater proportion of carbohydrates and fats, and are classed ascarbonaceous.
Roots and Tubers
Of the carbohydrates, next in importance to the sugars and to the starches in their purest form (corn starch, tapioca, sago, and arrowroot), come the roots and tubers, such as potatoes, sweet potatoes, beets, parsnips, turnips and onions.
The following table shows the proportion of various foodstuffs in these vegetables:
TABLE I—ROOTS AND TUBERS
Potatoes.It will be noted from the above table that sweet potatoes have a larger percentage of carbohydrates, hence they produce more heat and energy, than any other vegetable; next to the sweet potato, the Irish potato.
In the above table, the skins of the vegetables are included, and while the white potato contains two per cent protein, this is almost all located in a very thin layer immediately beneath the skin, so that when the potato is peeled in the ordinary way, the protein is removed. This holds true in many vegetables. They lose their distinctive flavor, as well as their value as tissue building foods, when the skins are removed. In baking a potato, the outerskin is readily separated from a less perceptible covering containing the protein, and this second skin should be eaten to get the full value and flavor.
In the white potato, of the twenty-two per cent carbohydrates three and two-tenths per cent is sugar and eighteen and eight-tenths per cent is starch. In the sweet potato, ten and two-tenths per cent is sugar and sixteen per cent is starch. Since sugar digests more quickly than starch, the sweet potato digests more quickly than the white. Because of the large per cent or carbohydrates in each, it is a mistake to serve these two vegetables at the same meal. For the same reason, bread and potatoes should not be eaten, to any extent, at the same meal, unless by one who is doing heavy manual labor, requiring much energy.
Onions.Only about four per cent of the onion represents nourishment; the eleven per cent of carbohydrates is made up of two and eight-tenths per cent sugar and the rest extractives. Of the extractives the volatile oil, which causes the eyes to water when peeling, is the most important. The onion is not, therefore, so important for its actual nourishing qualities as forits relish and flavor, and for this it is to be commended. It is a diuretic, encouraging a free action of the kidneys. Because of its diuretic value it is commonly called a healthy food. An onion and lettuce sandwich stimulates the action of the kidneys and is a nerve sedative.
The volatile oil makes the onion difficult for some to digest and, in that case, should be omitted from the diet.
Beets.There is no starch in beets, the seven and three-tenths per cent carbohydrates being sugar; they possess, therefore, more nutritive value than onions, and they are easily digested. It will be noted that it takes many beets to make a pound of sugar.
There are no more delicious nor nutritive greens than the stem and leaf of the beet. These greens contain much iron and are valuable aids in building up the iron in the blood, thus correcting anaemia.
Carrots.Carrots are valuable as food chiefly on account of their sugar. They are somewhat more difficult of digestion than beets and they contain more waste. They make a good side dish, boiled and served with butter or cream.
Turnips.Turnips have little value as a food. Their nutriment consists in the sugar they contain. For those who enjoy the flavor they are a relish, serving as an appetizer, and, like the onion, are to be recommended as a side dish for this purpose.
Parsnips.Like carrots, parsnips are chiefly valuable for their sugar and for the extractives which act as appetizers.
Since turnips, carrots, onions, and parsnips owe a part of their value in nutrition to the extractives which whet the appetite for other foods, it follows that, if one does not enjoy the flavor or the odor, these vegetables lose in value to that individual as a food. If one does enjoy the flavor, it adds to their food value.
Green Vegetables
The question may be asked with reason: “Why do we eat green vegetables?” They contain only about four per cent nutrition, as will be seen by the chemical analysis in the following table, and are mostly made up of water and pulp. It will be noted from the table that they are distinctly lacking in protein (nitrogenous matter) and in carbohydrates; hence, they have little foodvalue. Some of them have strong acids, thus increasing the alkalinity of the blood.
Their merit lies in the fact that they have distinct flavors and thus whet the appetite. Another reason why green vegetables are thoroughly enjoyed is because they come fresh in the spring, when the appetite is a little surfeited with the winter foods and one looks for green things.
TABLE II—GREEN VEGETABLES
All fresh vegetables should be masticated to almost a fluid consistency; otherwise, they are difficult of digestion, containing, as they do, so much pulp.
They are diuretic, helping the kidneys and the skin to rid the system of waste, and they are more laxative to the intestinesthan the root vegetables, partly because of the salts which they contain and partly because of the undigested vegetable fibre, which helps to move along the waste in the intestines. This vegetable fibre, being coarse, assists in cleansing the mucous lining of stomach and intestines, and, if for no other reason than for this cleansing of kidneys and intestines in the spring, when the system is most sluggish, the use of green vegetables is to be commended.
In larger cities, fresh vegetables are in the markets the year around, but if they are raised in greenhouses, or in any way forced, they lack the matured flavor and they also lack the iron which the rays of the sun give. If raised in the south and shipped for a distance, they are not fresh and they do not have as good an effect upon the system as when fresh and fully matured by the sun.
All greens, as spinach, chard, dandelions and beet tops, as previously stated, contain iron and build red blood corpuscles.
It is well, then, to eat freely of fresh vegetables in their season, even though they do not appreciably build tissue or furnish energy. By their effect upon theblood, the kidneys, skin, and intestines, they make sluggish vital organs more efficient.
Tomatoes and rhubarb are often, and with reason, classed under fruits.
Fruits
Technically speaking, fruits include all plant products which bear or contain a seed. They are valuable for their acids and organic salts—citrates, malates, or tartrates of potassium, sodium, magnesium, and calcium. In the juices of citrous fruits, are citrates of above minerals.
The fruit juices are readily absorbed and carried at once to the liver, where the sodium, magnesium, and potassium are released and the acids oxidized and changed to carbonates. They increase the alkalinity of the blood. These alkalis are soon eliminated through the kidneys, which accounts for the diuretic effect of fruits.
The seeds in the small fruits are not digested, but they serve the purpose of increasing intestinal peristalsis and of assisting the movement of the contents of the intestines. The skin and the fibre of fruits also assist the intestines in this way, just as the fibre in vegetables does.Fruits may be classified into acid and sweet fruits. Underacid fruitsare the citrous group—lemons, limes, grape fruit, oranges, cranberries, gooseberries, whortleberries, pineapples, currants, and rhubarb—if rhubarb is to be classed as a fruit.
There has been a commonly accepted theory that where a blood test shows evidence of too much uric acid, acid fruits are to be avoided, but the reverse is true. It has been fully demonstrated that the use of acid fruits increases the alkalinity,—or neutralizes the acids in the blood.
In case of an excess of hydrochloric acid in the stomach, lemon, or citrous fruits are valuable about half an hour before a meal as they decrease the secretion of the hydrochloric acid into the stomach. Where hydrochloric acid is limited, acids are given after a meal to supplement the deficient amount.
The sweetening of acid fruits does not detract from the value of the acids or of organic salts.
All acid fruits stimulate the action of the kidneys and the skin,—particularly lemons, limes, grape fruit, and oranges, and wherever the kidneys and skin are not sufficiently active, these fruits should be eaten freely.
It is difficult to make a decided distinction between sweet and acid fruits. The best guide is in the amount of sugar required to make them palatable. Some species of cherry are distinctly sour, while others are sweet. The same is true of apples, peaches, plums, etc.
Undersweetorblandfruits are pears, raspberries, grapes, bananas, blackberries, blueberries, melons, apricots, and some peaches, apples, and plums.
The large majority of fruits do not contain sufficient sugar to make them valuable for nourishment. Their chief value is in their appetizing flavor, and in the acids, and salts. Dates, figs, prunes, and dried grapes (raisins) are exceptions. As will be noted by the following table, these fruits contain a large amount of carbohydrates in the form of sugar. The larger amount of protein in these sweet fruits is largely in the seeds and, as the seeds are not digested, they have no real food value to the individual.
Figs and prunes are laxative,—probably the laxative effect of figs is due to the seeds, and of prunes to the salts and acids. However, prunes are free from tannic acid.
TABLE III—FRUITS
Care should be exercised in selecting ripe fruits and those which have not started to decay. The difficulty with so many fruits, which must be shipped from a distance, is, that, in order to reach their destination in fair condition, outwardly,they are picked before ripe and there is too much tannic acid in them. When fruits are allowed to ripen on the trees, the tannic acid is changed to sugar and fruit juices. One test of a ripened apple is to cut it with a steel knife—if the blade turns black, or if the cut surface of the apple turns brown in a few minutes, it should not be eaten, for it indicates an excess of tannin. It is this tannin which gives the small boy, with his green apples, excruciating pains. It will be recalled that the tannin from the bark of trees, so toughens the elastic skin of animals that we can wear this skin for shoes. The effect upon the live skin of the stomach and intestines, from the tannin in food, is not pronounced in toughening the skin, because of the activity and resistance of live matter.
Bananas are commonly picked green, because they decay so quickly that if they were picked ripe they would spoil before reaching the northern markets. The above table shows that bananas contain nearly twenty-three per cent of carbohydrates, which, in an immature state, are largely starches. The natural ripening process changes the starch to sugar, thus making them more easily digested. The starch globules, when not matured on the tree,are not easily broken and are thus difficult of digestion. Baking breaks the globules; a baked banana is thus more readily digested.
As previously stated, in a mixed diet meat and eggs are the chief sources of nitrogenous foods. Next to these come the legumes.
Meat
Meat is almost all digested in the stomach by the gastric juice, which changes it into peptone. It is needless to say that it should be thoroughly masticated that there may be no delay in the prompt action of the gastric juice upon it. If any part passes into the intestine undigested, the process is continued by the trypsin of the pancreatic juice. The peptone is absorbed as peptone and after it passes through the inner coating of the intestines, it is changed back to protein and carried by the blood and lymph to all tissues of the body, where it is used for growth and repairs. As stated, any excessof protein above that needed for growth and repair, is oxidized in the blood, yielding energy and heat, and the waste is eliminated through the kidneys and the bile. The red blood corpuscles, which are nitrogenous, are broken down in the liver and discharged through the bile.
TABLE IV—ANIMAL FOODS
In the composition of meat, of course there is more or less fat, varying from two to forty per cent, according to the animal and to the condition at the time of killing.
It is possible to combine the fat and the lean of meat so as to meet the requirements of the body without waste. About ninety-seven per cent of the meat consumed is assimilated by the system, while a largepart of the vegetable matter consumed is excreted as refuse. The compounds contained in the animal foods are much like those of the body, therefore, they require comparatively little digestion to prepare them for assimilation—this work having been done by the animal—while the vegetable compounds require much change by the digestive system before they can be used in the body.
Fish and sea foods are, many of them, rich in protein, as seen by the above table. Note that sardines contain the largest proportion of protein and next to these, shad roe.
There is a prevalent idea that fish is brain food. In so far as fish is easily digested, it builds brain tissue, but no more so than beef, or any food containing a goodly proportion of protein, easily digested, absorbed, and assimilated.
Lobsters are difficult of digestion and they contain little nutrition, so they are not valuable as a food.
Oysters, raw, are easier to digest than when cooked. Oysters should not be eaten during the spawning season from May to September.
Roasted flesh seems to be more completely digested than boiled meat, but rawmeat is more easily digested than cooked. Roasted chicken and veal are tender, easily masticated, and easily and rapidly digested in the stomach. This is one reason why the white meats are considered a good diet for the sick-room, especially in the case of stomach difficulty. Fat meats remain in the stomach a much longer time than lean meats; thus, gastric digestion of pork, which is largely fat, is especially difficult. Fried pork, in which the fat is heated to a very high degree, is very difficult of digestion. (See page197).
The chief objection to pork, however, is that hogs are scavengers and live upon all sorts of refuse. Another objection is that in preparing hogs for the market, the effort of the farmer is to force the feeding and get them as fat as possible. This excess of fat may result in degeneration of the meat tissue. The latter objection does not hold, however, for hogs carefully fatted for home consumption, or for hogs which run in the forests and live upon nuts, as do the beech fed hogs of the south.
The best meats are from young animals which have been kept fat and have not been subjected to any work to toughen the muscles.
Preserved and canned meats should be eaten with the utmost caution, not only because of the inferior meat used in the preparation of these foods, but also from the fact that they may become putrid after being canned.
The proportion ofalbuminoids,gelatinoidsandextractivesin meat vary with different meats and with different cuts of the same meat.
Thealbuminoidsof meat include the meat tissue, or the muscle cells. These constitute by far the greater part of the meat.
Thegelatinoidsare the connective tissue forming the sheath of the muscle and of bundles of muscles, the skin, tendons, and the casein of bone. Gelatines are made from these and, if pure and prepared in a cleanly manner, they are wholesome.
Gelatin is distinguishable in rich meat soups, which jelly upon cooling.
While the gelatinoids are not muscle, they keep the muscles from being consumed when starches, sugars, and fats are lacking, and, in this sense, may be considered more in the nature of carbohydrates.
Theextractivesconsist of a substance within the lean meat, known as creatin.This creatin is not a food; it is an appetizer, and gives to cooked meats, broths, etc., their pleasing flavor. In case of anaemia where it is necessary to build up red blood corpuscles, it is desirable to have the patient take the blood of beef, the thought of which is usually repellant, but it may be made very palatable if it is heated sufficiently to bring out the extractives, or flavor, and then seasoned.
Unless the beef extracts on the market contain the blood tissue in addition to the extractives, they are not particularly nourishing and are only valuable in soups, etc., as appetizers.
One reason why meat soups constitute the first course at dinner is because the extractives stimulate the appetite and start the flow of gastric juices. Bouillons contain no nourishment, because the proteins have been coagulated by the vigorous boiling, but they may be used as a basis for vegetables, rice, or barley to give them flavor.
The best method is to make one’s own soup from the connective tissues (gelatinoids) and meat tissue.
Eggs
Eggs consist chiefly of two nutrients,—protein, and fat (ten per cent), combined with water, phosphorous, and ash.Eggs are a wholesome source of protein and are, therefore, classed as nitrogenous foods.
The fat and the iron are in the yolk, which is about one-third fat. The yolk also contains phosphorous and some ash. The white is practically free from fat but contains sulphur, phosphorous and a very little ash. The white and the yolk contain almost equal quantities of protein.
The white of the egg is said to be pure albumen; the chief ash constituent is common salt. The total phosphorous in the white of the egg is equivalent to about two per cent phosphoric acid and the total phosphorous in the yolk is equivalent to one per cent.
The dark stain made by eggs on silver is due to the sulphur contained in them. The iron in the egg is valuable to assist in building red corpuscles.
The large part of the egg, as other proteins, is changed, mostly in the stomach, into peptone, absorbed as peptone and then changed back again into protein after absorption. That not digested in the stomach is changed in the intestine, as is the case with other proteins.
Eggs are, no doubt, excellent articles of food for nutrition and for tissue building.They contain more water than cheese, but are more concentrated than milk or oysters. They have practically the same relative value in the diet as meat, and make a very good substitute for meat. Egg yolk in abundance is often prescribed where it is necessary to supply a very nutritious and easily assimilated diet.
One of the best methods of preparing eggs, which is especially valuable for those having delicate stomachs or for those who need to build up red blood corpuscles with the iron in the yolk, is in egg lemonade or orangeade. Thoroughly beat the egg, add the juice of half a lemon or orange, sugar to taste, and fill the glass with water.
The citric acid in these fruits partly digests the egg, changing it into egg albumin,—the egg becomes limpid, no longer stringy. From this condition the gastric juice quickly changes it to peptone.
Grape juice, cream, and cocoa may be used in place of lemon or orange, in order to give variety where it is necessary to take many of them, but the grape juice acid does not partially digest the egg as the juice of the lemon does.
Eggnog is another means of taking raw eggs.
One method which any housewife can use to test the freshness of eggs is to drop them into a strong, salt brine made of two ounces of salt to a pint of water. A fresh egg will at once sink to the bottom. After the third day the surface of the shell will be even with the surface of the water and with increasing age they will rise still higher.
There is a prevalent opinion that if an egg is boiled hard it is difficult of digestion, but this depends entirely upon the mastication. If it is masticated so that it is a pulp before swallowed, a hard boiled egg is digested as readily as a soft boiled one. If it is not thoroughly masticated, then an egg should not be boiled longer than three to four minutes, or should be put into boiling water and allowed to remain in the water for six minutes without actively boiling. The latter method cooks the egg through more evenly. Another method of cooking the yolk evenly with the whites is to put the egg in cold water, let it come to a boil, and then again immerse in cold water. Or the egg may be put in cold water, let come almost to a boil, removed from the stove, and let stand ten to twelve minutes in the hot water. Any one of thelast three methods cooks the white and the yolk evenly.
Under this class come cereals, legumes, nuts, milk, and milk products. In these foods the nitrogenous and carbonaceous elements are more evenly proportioned than in either the carbonaceous or nitrogenous groups. The different food elements in this group are so evenly divided that one could live for a considerable length of time upon any one food. Some animals build flesh from nuts alone, while the herbivorous animals live upon cereals and plants.