The value of a knowledge of food and its effect in the human body cannot be overestimated. In health, this knowledge leads to higher standards, since by pointing out the errors in one’s mode of living, good health habits may be established, which will, undoubtedly assure the individual of a better nourished and a more vigorous body.

There is no question as to the value of health either from the standpoint of comfort or of economy. And the knowledge which will enable one to spread the good work intelligently cannot but raise the standards of living throughout the entire community.

In taking up the study of dietetics, the student is introduced to some of the fundamental principles governing the health and well-being of a people, since dietetics includes a study of food and its relation to the body.

The relationship between right food and good health is very close; how close is being demonstrated constantly in experimental fields of scientific research.

To be able to judge whether the food one eats daily is giving the best possible value from a physiological and economic standpoint, requires a definite knowledge of food, its source, composition and nutrient value, as well as its relation to the body in health and disease.

No one is capable of giving constructive advice upon matters pertaining to diet, unless he has acquired this knowledge through training. A nurse should obtain this training during her course in the hospital, through the class room, the wards and the diet kitchen. The dividing line between health and disease is frequently almost imperceptible, and without a knowledge of the normal body, it is, at times, impossible to tell where the normal leaves off and the abnormal begins. For this reason a nurse must understand normal nutrition, that is, the behavior of food in the healthy body, before undertaking the task of ministering to the body attacked by disease.

In a text of this kind, it is impossible to cover all phases of the subject, especially since day by day new discoveries are being made with relation to food and its uses in the body. But with careful attention to the principles set forth, a nurse should be able to carry out the dietary orders given her by the physician and dietitian in the hospital. And, when her course of training is finished, she should find herself equipped to assist in raising the standard of health through her knowledge of dietetics. With this brief summary of the aims and object of the study of dietetics, we will begin the actual work with a study of Food.

Food Materials.—Food is the name given to any substance which, taken into the body, is capable of performing one or more of the following functions:

For the convenience of study scientists have arranged the foodstuffs in groups:

All foods are composed of certain chemical elements; namely, carbon, oxygen, hydrogen, nitrogen, sulphur, phosphorus, iron, magnesium, potassium, chlorine, sodium, calcium, with traces of various others. The manner in which these elements are combined and the amounts in which they occur determine the group to which the combination belongs, and give to the foodstuff its characteristic position in human nutrition.

COMPOSITION OF THE FOODSTUFFS

The chemical elements are combined in food and in the body, as: (a) carbohydrates, composed of carbon, oxygen and hydrogen; (b) fats, composed of carbon, oxygen and hydrogen; (c) proteins, composed of carbon, oxygen, hydrogen, nitrogen and sulphur; (d) water, composed of hydrogen and oxygen; (e) mineral salts. The first three foodstuffs constitute the Organic Food group. The last two include the remaining chemical elements, calcium, phosphorus, sodium, potassium, chlorine, magnesium, iron and traces of others which make up the Inorganic Food group.

Each of the foodstuffs belonging to the organic group is capable of being burned in the body to produce heat for: (a) the maintenance of the body temperature; (b) internal and external work.

Neither water nor mineral salts alone can be burned to produce heat; nevertheless, they enter into the composition and take part in every function performed by the carbohydrates, fats and proteins; therefore one foodstuff cannot be said to be of greater importance than another, since the needs of nature are best met by a judicious combination of all. However, the wear and tear of life can be more efficiently accounted for, and the strain upon the organism reduced more nearly to a minimum when the various foodstuffs are furnished in amounts which science is proving to be necessary for the health and well-being of the organism.

The sixth essential food substance, the Vitamines, together with the adjustment of the five foodstuffs just mentioned—the amounts and types of each in the dietary which will assure the body of the best results—has been, and still is a subject of grave interest. Even on the most perfect adjustment of these foodstuffs, the diet would fail to give the desired results without the inclusion of the sixth, or vitamine factor, which has proved to be essential for the growth and development of the normal body, as well as for its protection against certain deficiency diseases.

In order to obtain the best results from food, both from a health and an economic standpoint, it is necessary to become familiar with the foodstuffs as they are combined to make up the various common food materials. One foodstuff may be a producer of heat, but may lack certain chemical elements which are essential to the building of tissues; another may be able to accomplish both functions in the body, but will prove too expensive to use as fuel, except when it is absolutely necessary to do so. Thus, it is essential for the nurse to understand where and how both the foodstuffs and the vitamines occur in nature, in order to make use of them more advantageously. The following table gives the sources of the foodstuffs, after which a description of the individual foodstuffs and vitamine factors will serve to point the way to their use in the dietary:

THE INDIVIDUAL FOODSTUFFS AND VITAMINE FACTORS

A study of the individual foodstuffs and vitamines will furnish the first link in the chain which constitutes our present knowledge of dietetics.

CARBOHYDRATES

In the ordinary mixed diet of man, the carbohydrates predominate, being not only the most abundant, but also the most economical source of energy. The term carbohydrate covers all of the simple sugars and those substances which can be converted into simple sugars by hydrolysis; the ones of special interest in this study are divided into three groups, known as, Monosaccharides (C₆H₁₂O₆); Disaccharides (C₁₂H₂₂O₁₁) and Polysaccharides (C₆H₁₀O₁₅).

Monosaccharides.—Glucose, Fructose and Galactose are substances whose monosaccharide molecules contain one sugar radical; hence they cannot be hydrolized to simpler sugars (sugars of lower molecular weight). Those constituting this group of sugars are all soluble, crystallizable and diffusible substances, which do not undergo changes from the action of the digestive enzymes, consequently these sugars will enter the blood stream in their original form, unless attacked by the bacteria which inhabit the stomach and intestinal tract. The monosaccharides are all susceptible to alcoholic fermentation. Each member of the group is utilized in the body for the production of glycogen and for the maintenance of the normal glucose of the blood.

Disaccharides.—Sucrose, Maltose and Lactose are substances yielding, upon hydrolysis, two molecules of simple sugar: each of these sugars is crystallizable and diffusible: all are soluble in water, and to a less degree in alcohol—sucrose and maltose are more soluble than lactose. When attacked by the digestive enzymes, these sugars are changed to monosaccharides.

Polysaccharides.—Starch, Dextrin, Glycogen and Cellulose are substances more complex in character than the above-mentioned groups. They are built up of many sugar molecules, which yield upon complete hydrolysis many molecules of simple sugar. The polysaccharides are insoluble in alcohol, and only soluble to a certain extent in pure water. Some members of this group swell and become gelatinous in the presence of moisture and heat; some become of a colloidal form in water, and will pass through filter paper; others remain unchanged.

A brief description of the various members of these different groups of carbohydrates will assist the nurse in the ways and means of utilizing them in the dietary to the best advantage.

Glucose, which is abundant in the juice of plants and fruits, and to a more or less degree in the blood of all animals (usually about 0.1%) occurs free in nature. This sugar is likewise obtained from many carbohydrates, either through the action of acids, or as the result of the digestive enzymes, and as such becomes the principal form in which the animal body utilizes the carbohydrates ingested. Under normal conditions the glucose in the blood is constantly being burned and replaced; it is only when the body loses to a greater or less degree the ability to burn the glucose that it accumulates in the blood, from which it must escape by way of the urine. There are times, such as when very large quantities of carbohydrates are eaten at once, when glucose will also appear in the urine; but under such circumstances it is generally found to be merely temporary, and for this reason, the condition is known as temporary glycosuria. As a rule, however, the surplus of glucose absorbed, whether it be eaten as such, or is found as the result of enzymic action upon the other carbohydrates, is converted into glycogen and stored in the liver and to a less extent in the muscles. Glycogen is readily reconverted into glucose, which is used by the body for the production of energy. It has been estimated that over half the energy manifested in the human body is derived from glucose, and it is in this form that the tissues of the body will ultimately make use of most of the carbohydrates in food. Practically all of the fruits, and many of the vegetables, are rich in this form of carbohydrate, but grapes contain more than any of the other fruits, while sweet corn, onions, and unripe potatoes contain appreciable amounts.

Fructose.—The second member of the monosaccharide group is more or less associated with glucose in plant and fruit juices, and is used like that substance for the production of glycogen in the body. Eaten as such, or produced as the result of digestive action upon cane sugar, fructose is changed into glycogen, chiefly upon entering the liver, and for this reason will not be found to enter largely into the blood of the general circulation.[3]

Honey is the most abundant source of fructose in nature.

Galactose.—This sugar, unlike the other members of this group, is not found free in nature, but it is produced as the result of hydrolysis of milk sugar, either by enzymes or by acids. Like glucose and fructose, galactose seems to promote the production of glycogen in the body. Certain substances known as galactosides, which are combinations of galactose and some substances other than carbohydrates, are found in the nerve and brain tissues of the animal body.

Disaccharides.—Of the second group of carbohydrates, we are probably more familiar with sucrose, or cane sugar, than with either of the other two, since it is in this form that the greater part of the sugar eaten is purchased.

Sucrose.—By far the greater part of the sugar entering into the average dietary is manufactured from sugar and sorghum canes, and from sugar beets; but appreciable quantities are derived from the sugar maple and sugar palms. Many of the sweet fruits are rich in this form of sugar; pineapples are said to contain at least half of their solids in sucrose; and although other fruits and vegetables do not contain so high a percentage of this sugar, oranges, peaches, apricots, dates, raisins, prunes, carrots and sweet potatoes contain goodly quantities, which are associated with glucose and fructose. Sucrose is readily hydrolized, either by acids or enzymes. The inverting enzyme (invertase) of yeast and sucrase of the intestinal juice, convert sucrose to fructose and glucose, in which forms it is absorbed into the portal blood. It is believed that when sucrose is eaten in very large quantities, it is sometimes absorbed from the stomach. In these cases it does not become available for use in the body, but acts in the same manner as when injected directly into the blood stream, being excreted unchanged by way of the kidneys. According to Herter, sucrose is much more susceptible to fermentation in the stomach than either maltose or lactose; and since it has no advantage over these sugars from a standpoint of nutrition, they are frequently substituted for sucrose in cases where the dangers arising from fermentation must be avoided.

Maltose (Malt sugar) is an important constituent of germinating grains—malt and malt products being formed as the result of enzymic action (amylases) on starch. A similar action takes place in the mouth as the result of the ptyalin in the salivary juices and in the intestines from the action of the starch-splitting enzyme, amylopsin, in the pancreatic juice. The maltose thus formed is further converted into glucose by the sugar-splitting enzyme in the intestinal juice, and in this form it is chiefly absorbed. Maltose is also an intermediate product formed during the manufacture of commercial glucose as the result of the boiling of starch with dilute acids.

Lactose (sugar of milk) is one of the most important constituents in the milk of all mammals. In freshly secreted human milk, lactose occurs in quantities ranging from 6 to 7%, and in the milk of cows and goats from 4 to 5%. Lactose is much less soluble than sucrose, and decidedly less sweet; hence, owing to this latter property, as well as to its lack of susceptibility to fermentation, lactose is frequently used to bring up the sugar content of infant formulas to the desired percentage, and the diets used in the abnormal conditions when additional energy material is needed. During the process of digestion, lactose is hydrolized by the lactase in the intestinal juice, yielding one molecule of glucose and one of galactose. Like maltose, little if any of this sugar is absorbed in its original form, since experiments made with injections of lactose into the blood result in the rapid and almost complete elimination by way of the kidneys. No such results are obtained when even large amounts of lactose are taken by way of the mouth.

Polysaccharides.—This group of carbohydrates is complex in character, built up of many sugar molecules, and upon digestion must be broken down into simple sugars before they can be utilized by the body.

Starch is the form in which the plant stores her supply of carbohydrates. It is found in this form in roots and (mature) tubers, three-fourths of the bulk of which is made up of this material. From one-half to three-quarters of the solids of grains is made up of starch also. Pure starch is a fine white powder, odorless and almost tasteless. It is insoluble in cold water and alcohol, but changes from an insoluble substance to a more soluble one upon the application of heat. Upon hydrolysis starch gives first a mixture of dextrin and maltose, then glucose alone as an end-product. This hydrolysis may be the result of enzymic action, as occurs upon bringing starch in contact with the ptyalin in the saliva, or with the amylopsin in the pancreatic juice; or it may be the result of boiling starch with acid, as is seen in the manufacture of commercial glucose.

Dextrin, as has already been stated, is an intermediate product of the hydrolysis of starch by acid or enzymes.

Glycogen is the form in which the carbohydrates are stored in the body, just as starch is the form in which they are stored in plants. It is found in all parts of the body, but is especially abundant in the liver. Here it is stored in the cell substance rather than in the nucleus. The storage of glycogen in the human body depends largely upon the mode of life and upon the diet. Active muscular work, especially out of doors, uses up the store of glycogen with great rapidity; while rest and a sedentary life promotes its storage. The body readily converts its supply of glycogen into glucose, the form in which the body uses the carbohydrates for fuel.

Cellulose is a woody, fibrous material insoluble in water and to a certain extent impervious to the action of the digestive enzymes. This carbohydrate constitutes the skeleton of plants just as the bones constitute that of the animal body. It is probable that owing to the length of time required for this carbohydrate to be broken down in digestion, much of it escapes oxidation entirely. Hence, it passes down the digestive tract lending bulk to the food mass and thus promoting peristalsis throughout the whole of the digestive tract.

Organic Acids.—Certain of the carbohydrate foods (fruits and green vegetables) contain appreciable amounts of organic acids or their salts; oranges and lemons, for example, are rich in citric acid; grapes contain considerable quantities of potassium acid tartrate, apples and other fruits have malic acid; many of the fruits have succinic acid; a few foods contain oxalic acid, or oxalates. All of these organic acids are burned in the body to produce energy, with the possible exception of the oxalates, which seem to have little, if any, food value. According to Sherman, these organic acids have a lower fuel value, per gram, than carbohydrates, but are reckoned as such in computing a food in which they exist. The function of these acids is chiefly that of neutralizing the acids formed in the body in metabolism. Being base-forming in character, they function after absorption and oxidation in the body as potential bases—the base associated with the acid in their ash combining with carbonic acid to form carbonates, which act as above described.

Bacterial Action upon Carbohydrates of Foods.—The bacteria that act chiefly upon the carbohydrates belong to the fermentative type. The substances formed as a result of this activity are certain acids—lactic, butyric, formic, acetic, oxalic, and possibly alcohol. Certain forms of carbohydrates are more susceptible to bacterial fermentation than others. Herter claims that sucrose and glucose are much more so than lactose, maltose, or starch. The substances thus formed through bacterial activity are not believed to be toxic in character, but merely irritating. However, the irritation arising from excessive fermentation in the stomach may lead to gastric disturbances of a more or less serious nature; hence the amount of carbohydrate taken under certain conditions must be adjusted carefully. The Effect of Heat upon Carbohydrates.—The changes wrought in the carbohydrates as a result of heat have already been discussed to a certain extent. It is seen that the sucrose (cane sugar) is soluble alike in hot and cold water; the same is true of maltose; but lactose is much more soluble in hot water than it is in water which has not been heated. So far as their digestibility is concerned, the application of heat (boiling) neither increases nor decreases the utilization of these sugars by the body.

With starch it is an entirely different matter. It has been found that the application of heat, either as dry heat, or in the presence of moisture, brings about a definite change in the character of the foodstuff. Pure starch admixed with water and boiled, passes into a condition of colloidal dispersion, or semi-solution, known as starch paste (Sherman). This is graphically illustrated in the cooking of potatoes, in which the starch and water are mixed in nature; and in the cooking of cereals and like starchy foods, to which water is added in preparation for their cooking. In both cases the application of heat adds greatly to the digestibility of the raw material by reason of the change which is wrought in these substances, causing them to be more readily acted upon by enzymes in the digestive juices.

This solubility of carbohydrates in hot water may be utilized in the washing of utensils in which these substances have been prepared; thus saving much time and effort on the part of the nurse in either the diet kitchen or in the home.

FATS

The second member of the organic food group, and one which is almost as widely distributed throughout animal and vegetable life as the carbohydrates, is found in the fats. This foodstuff, while composed of the same chemical elements that go to make up the carbohydrates, contains these elements in different proportions; that is, fats contain less oxygen and more hydrogen than carbohydrates.

Typical Fats.—The fats (as already shown in the Table on page 5) are derived from both animal and plant life, but, like the carbohydrates, do not always occur in the same form. Those of animal origin include:

Adipose Tissue of man and animals, tallow of mutton, suet, and oleo oil of beef, lard of pork.

Phosphorized Fats, which include lecithin and lecithans, occur abundantly in the brain and nerve tissues and to a less extent in the cells and tissues of man, animals, and plants of which it seems an essential part. Egg yolk is the most abundant source of phosphorized fat in food material, but milk likewise furnishes an appreciable amount.

Cholesterol (fat-like substances).—“The fatty secretions of the sebaceous glands of man and of the higher animals which furnish the natural oil for hair, wool and feathers,” (Starling), lanoline, which is a purified wool fat, consist chiefly of cholesterol. According to Mathews, cholesterol is an essential constituent of the blood, and is found in the brain and in nearly all living tissues. It is likewise believed to be the “mother substance” from which bile acids are derived.

Fat Soluble “A.”—The vitamine factor which occurs dissolved in certain fats, namely, milk (whole), butter, egg yolk, the organs of animals, and codfish liver.

Definition of Fat.—The fats are all glycerides; that is, they are substances made up of combinations of fatty acids and glycerine, which constitute a definite group of chemical compounds, certain members of which are liquid in form, while others are solid, or semi-solid. The liquid fats are known as fatty oils. The fatty acids in which we are chiefly concerned in this study are: Butyric, Stearic, Oleic, and Palmitic. Most of the common fats owe their form and flavor to the type and amount of the various fatty acids of which they are composed. For example, butter is made up of ten fatty acids; but its soft, solid form is due to the olein and palmitin (glycerides of oleic and palmitic acids) which it contains; and its characteristic flavor, as well as its name, to its butyric acid content (about 5 to 6%). It is evident that the degree of softness or hardness of a fat may be determined chiefly by the amount of oleic acid in its composition. Most of the common oils with which we are familiar in food are composed chiefly of olein. Stearin (the glyceride of stearic acid) is the hardest of the fatty acids, while palmitin, although classed with the solid fats, is not so hard as stearin. Lard and butter are higher in olein and palmitin and are consequently semi-solid, while suet and tallow, consisting chiefly of stearin, are much harder than the other food fats.

Characteristics of Fats.—The fats are all insoluble in water, and only partially so in cold alcohol, but they dissolve readily in ether. As a rule, the fat occurring in the animal body is more or less characteristic of the species. For example, animals that live on land have a harder fat than those living in the water; warm blooded animals, harder fats than cold blooded ones (fish); and carnivorous animals, harder fats than herbivorous species.

Fats are lighter than water, hence will float in it. An emulsion is a suspension of fat in a fluid, and the fat in this case must be very finely divided and mixed with some other material which will prevent a coalescence of the fat globules. In milk, which is one of the best natural emulsions, the additional substance is protein.

Effect of Heat upon Fat.—When fats are brought to a high temperature, the glycerine which they contain decomposes with the production of a substance known as acrolein, which has an irritating effect upon the mucous membranes. It is possible that the over-heated fatty acids add their quota to the production of irritating fumes. As a rule, it is inadvisable to use frying as a method of preparing food for the sick or for children. Doubtless, if every cook understood the exact degree of heat to apply in frying, and knew just how moist to have the food mixture which she intended to cook in this manner, better results would be obtained; but since the average cook knows little about the scientific application of heat to fat or the changes brought about thereby, it is safer to make use of other methods of food preparation under the circumstances.

Functions of Fat.—This foodstuff undoubtedly serves as the most compact form of fuel available to the body for the production of energy. Weight for weight, fat furnishes twice as much heat as the carbohydrates, and in bulk the difference is even more striking; for example (about) two tablespoonfuls of sugar are required to produce 100 calories, whereas one scant tablespoonful of olive oil will produce a like number of heat units. As a source of supply for reserve energy in the body, fat is most valuable. This reserve fuel is stored in the form of adipose tissues underlying the skin and surrounding the vital organs, lending contour to the form and protecting the organs from jars and shocks. Distributed throughout the body, fat may be found as (a) cholesterol (in the cells of the muscles, organs, and nerve tissues), which acts as a protection against the destruction of the red blood cells; (b) phosphorized fat (lecithin), the universal distribution of which, according to Starling, seems to indicate that it plays an important part in the metabolic process of the cells, serving as a source of phosphorus which is required for the building up of the complex nucleoproteins of the cell nuclei.

PROTEINS

Upon investigation it was found that neither the fats nor carbohydrates were the chief constituents of the active tissues. It was found, in fact, that the carbohydrates occurred in very small quantities only in the muscles, and that frequently the quantity of fat was likewise limited. Other substances, containing nitrogen and sulphur in addition to carbon, oxygen, and hydrogen, which were invariably present, and which are essential constituents of all tissues and cells, both in animals and in plants, must be necessary to all known life. To these substances, believed at the time to be the fundamental constituents of all tissues, Mulder gave the name Protein, from the Greek, meaning “to take first place.” Later investigations proved that, while the proteins were essential to the building and repairing of the tissues and cells in general, they were not the only factors concerned in the work; that certain mineral salts were necessary constituents of all tissues, and must be present in order for any normal growth and development to occur.[4]

Composition of Proteins.—The average nitrogen content of common proteins is about 16%; that is, in 100 grams of protein there will be approximately 16 grams of nitrogen, or in 6.25 grams of protein there will be 1 gram of nitrogen. To estimate the protein content of a food when the percentage of nitrogen is known, it is necessary simply to multiply the percentage of nitrogen present, by the nitrogen factor, 6.25; or, if the amount of nitrogen is desired, when the percentage of protein is given, to divide by same factor.

Construction of Proteins.—In plant structure the building up of the proteins is accomplished by the plants from inorganic substances existing in the soil and air; but in the animal body this is not possible, because the construction of the tissues requires the use of other proteins—the most available ones being found in food. Each animal (or species) forms the proteins characteristic of its own tissues,—while the proteins of food are similar to those found in the body, they cannot be utilized in their original form, but must be split into simpler substances from which the cells of the various tissues throughout the body may select those particularly adapted for their purpose. These transformed substances are known as amino acids, the production of which is a result of digestion in the digestive tract. There are about seventeen of these acids entering into the construction of the common proteins. One scientist has likened these units to letters of the alphabet, which, being combined, spell many proteins. When a protein contains all of the essential units, it may be said to be “complete,” the best example of which may be seen in milk, eggs, and meat. When a protein lacks some of the essential elements, or letters of the protein alphabet, it is said to be incomplete. Gelatin is the best example of this type of protein, but the cereals and beans must likewise be supplemented by other substances; milk being the one most generally used for this purpose. For the purpose of building young tissues, and maintaining those already mature, it is logical to use foods containing the foodstuffs in their best form; that is, those that not only contain the complete protein, but also the requisite mineral salts and vitamines. Foods lacking in some of these respects become adequate when supplemented by these foods which can supply the missing constituents; hence, the use of such incomplete protein foods need not necessarily be abandoned, for, as in the case of cereals, the foods are both economical and palatable, and, when used in addition to milk, furnish valuable adjuncts to the dietary.

Classification of Proteins.—A brief description of some of the more important proteins with which we are chiefly concerned will serve to simplify the formulation of a diet. Those assuming the most important position in nutrition and food are globulins, albumens, nucleoproteins, phosphoproteins, hemoglobins, and derived proteins such as proteoses and peptones. The albumens and globulins associated together occur in the tissues of both animals and plants. The albumens are richer in sulphur than the globulins and are found more abundantly in the animal fluids, such as the blood, while the globulins predominate in the more solid tissues of animals and in plants. The close association of these two proteins is particularly noticeable in the blood and cells. They have different characteristics, however.

Albumins.—The best examples are found in egg albumin (white of egg), lactalbumin (milk), serum albumin (blood), leucosin (wheat), legumelin (peas). Albumins are all soluble in pure water, and are coagulable by heat. Coagulation, due to the action of the ferments in the body, takes place in milk, blood, and muscle plasma. Certain albumens are particularly adapted for the building and repairing of tissues. Among those that have been used in feeding experiments to determine whether or not they were capable, when used as the sole protein in the diet, of maintaining animals in normal nutrition, and of supporting normal growth in the young animal,—may be cited lactalbumin and egg albumin. These experiments provided diets adequate in other respects, the object being to determine the value of the various proteins. It was found that the albumin from milk was more efficient in this respect than the egg albumin.[5]

In the invalid dietary the solubility of the albumins in water makes them of especial value as reinforcing agents, since they may be introduced into fluids without materially altering either their flavor or their bulk.

Globulins.—Simple proteins, insoluble in pure water, but soluble in neutral salt solutions; examples, muscle globulin, serum globulin (blood), edestin (wheat), physelin (beans), legumin (beans and peas), tuberin (potatoes), amandin (almonds), arachin, and conarachin (peanuts).

Alcohol-Soluble Proteins.—Simple proteins soluble in alcohol of from 70-80% strength. Insoluble in absolute alcohol, water and other neutral solvents. Examples of these proteins may be seen in the gliadin of wheat, zein of corn, and hordein of barley.

Albuminoids.—These substances represent one group of incomplete proteins, inasmuch as they cannot alone support protein metabolism. However, they are classed with the proteins and may be substituted for at least a part of these compounds in the daily dietary, since they are able to do much of the work of the pure proteins. The best example of this group is seen in gelatin. This substance contains many of the structural units of meat protein but in very different relative amounts. It has not, therefore, the chemical units necessary to repair the worn-out parts of cell machinery.[6]

Conjugated Proteins:—Nucleoproteins, Phosphoproteins and Hemoglobin.

(a) Nucleoproteins.—This type of protein is characteristic of all cell nuclei, and is particularly abundant in the highly nucleated secreting cells of the glandular organs, such as the liver, pancreas, and the thymus gland. The nucleoproteins are composed of simple proteins and nuclein. Nucleic acid is rich in phosphorus and upon decomposition yields some of the purin bases (xanthin, adenin, guanin), a carbohydrate and phosphoric acid.[7]

(b) Phosphoproteins.—Compounds in which the phosphorus is in organic union with the protein molecule otherwise than a nucleic acid or lecithin. Examples: caseinogin (milk), ovovitellin (egg yolk). (c) Hemoglobin.—Much of the greater part of the iron existing in the body occurs as a constituent of the hemoglobin of the red blood cells. When the intake of iron is not sufficient to cover the output, there must be a consequent diminution in the hemoglobin of the blood with a corresponding development of anemia.

The importance of knowing these characteristic proteins is apparent. Not only will such knowledge lead to a more intelligent use of protein foods in the normal dietary, but it will prove of the greatest assistance in the adjusting of the foodstuffs in diet for individuals suffering from certain abnormal conditions.

In abnormal conditions this knowledge of the various proteins—their composition, source, and behavior in the body assumes a position of the greatest importance; since it represents the means for safeguarding a patient from the results caused by the wrong kind of food. In certain types of nephritis, for example, it is perfectly safe to give milk where the ingestion of meat and eggs might cause serious, if not fatal, results. In treating gout, when it is deemed advisable to limit the purin foods in order to control in a measure the retention of uric acid in the body, the realization that certain of the nucleoproteins, upon being broken down in the body, yield the purins, which in turn give rise to the production of uric acid, will permit the nurse to adjust the diet so as to eliminate such foods entirely (see Gout). The importance of keeping the hemoglobin content of the blood normal has already been mentioned.

The Effect of Heat upon Proteins.—The fact that certain proteins are most susceptible to heat has already been stated, but the application of this knowledge in the preparation of protein foods is important. In milk, for example, whole raw milk forms a large hard curd; whereas boiled milk curdles in a much finer and softer form. Pasteurized milk shows smaller curds than raw whole milk, but larger than the boiled whole milk.[8]

An egg cooked by the application of a long-continued high temperature (212° F.) has a tough white; whereas an egg cooked until hard at a temperature under the boiling point shows a tenderness in the white which renders it distinctly more palatable. Soft-cooked eggs leave the stomach in less time than is required for hard cooked ones; poached (cooked in water under the boiling point), shirred eggs (cooked in hot dish), and soft-cooked eggs are among the most readily digestible forms of eggs. Raw eggs are slightly less stimulating to acid secretion in the stomach and require a longer time to leave the stomach than boiled eggs. Thus it is seen that in many cases the difference in preparation of the protein foods may make a difference in the way in which the digestive tract handles them. Necessarily, this point is emphasized more in abnormal than in normal conditions; for example, albuminized orange juice gives rise to a distinct gastric secretion, and leaves the stomach rapidly—a great advantage in certain abnormal conditions, and especially in those requiring liquid diet of high nutriment value.

The knowledge of the coagulation of proteins by heat points out the advantage of using cold water over hot in the preliminary cleansing of utensils in which protein foods have been prepared. Certain members of this group are soluble in pure water, and will readily dissolve; whereas, if the water is heated, their coagulation would prevent this taking place so readily.

Functions of Protein in the Body.—The proteins serve two distinct uses in the body; first, that of building and repairing tissues and furnishing, in conjunction with other substances, material for growth; second, that of producing energy for the internal and external work of the body. For this latter function a large percentage of the proteins ingested is used; consequently, since the carbohydrates and fats are primarily the energy furnishing material most readily used by the organism, it is clearly demonstrated that the average individual takes more protein into the body than is necessary for its maintenance. Except during the period when an allowance for growth must be made, it is probable that a much smaller daily consumption of protein could be made without disadvantage to the organism, leaving the bulk of the work, in so far as the running of the engine is concerned, to the other organic foodstuffs.

WATER

Man can exist for days, even weeks, without food, but without water life soon becomes extinct. This substance is composed of hydrogen and oxygen in the proportion of two to one; that is, to each atom of oxygen there will be found two atoms of hydrogen. This is always the case no matter where it is found. When foods are put through a drying process the water is taken out and the rest of the chemical composition of the food remains unchanged.

This foodstuff, unlike those belonging to the organic group, is not changed during the process of digestion, nor does the application of heat or cold affect it, save from a physical standpoint. Water boils at a temperature of 100° C. (212° F.), and freezes at a temperature of 0° C. (32° F.).

Function of Water.—The uses of water in the body are many, and the advantage arising from a sufficient amount of this foodstuff in the dietary cannot be overestimated. It is no longer considered an error in diet to drink a moderate amount of water with the meals, so long as it is not used as a substitute for mastication, and as a means of washing the food into the stomach. In the diet, both as a beverage and as a part of most of the food materials ingested, water serves to moisten the tissues; to furnish the fluid medium for all of the secretions and excretions of the body; to carry food materials in solution to all parts of the organism; to stimulate secretory cells producing the digestive juices, thereby aiding in the processes of digestion, absorption and excretion; to promote circulation; to furnish material for free diuresis, thus preventing to a great extent the retention of injurious substances by the body, which might otherwise take place.

Factors Determining the Amount of Water Needed.—In normal conditions it is probable that the kind and amount of exercise taken has more to do with the amount of water needed by the body than any other factor, since the vigorously worked body excretes more water by way of the skin than the quiescent one. With a normal amount of exercise, it is advisable to drink from six to eight glasses of water each day, increasing the amount to a certain extent when exercise causes a great loss through perspiration. It is always advisable, however, to keep in mind that an excessive amount of fluid taken into the body throws a corresponding amount of work on the organs (the stomach, kidneys and heart). In certain abnormal conditions, the body’s water supply is depleted. This is particularly true in the case of hemorrhage, vomiting, and diarrhea. Under other conditions (certain types of nephritis), the body becomes overburdened through the excess of water retained, owing to the difficulty which the kidneys show in eliminating it. This retention of water by the tissues gives rise to the condition known as edema.

Ash.—The eight remaining chemical elements, i.e., calcium, magnesium, sulphur, iron, sodium, potassium, phosphorus, chlorine, constituting the mineral salts or ash, are likewise classed as food on account of the work which they perform in the body. Some of these elements enter the body as essential constituents of the organic compounds, and are metabolized in the body as such, becoming inorganic only upon oxidation of the organic materials of which they form a part.

Importance of the Mineral Salts.—The way in which the mineral elements exist in the body and take part in its functions, has been graphically outlined by Sherman as follows.

“(1) As bone constituents, giving rigidity and relative permanence to the skeletal tissues. (2) As essential elements of the organic compounds which are the chief solids of the soft tissues (muscles, blood cells, etc.). (3) As soluble salts (electrolytes) held in solution in the fluids of the body; giving to those fluids their characteristic influence upon the elasticity and irritability of muscle and nerve; supplying material for the acidity and alkalinity of the digestive juices and other secretions; and yet maintaining the neutrality, or slight alkalescence, of the internal fluids as well as their osmotic pressure and solvent power.”[9]

The above outline, showing the various ways in which the mineral constituents enter and take part in the various functions, as well as in the structure of the body, make it evident that the same close attention and study which was given to the other foodstuffs must be accorded to these substances. When the student realizes that the presence of certain salts dissolved in the blood assists in the regulation of the vital processes of the body such as the digestion, circulation and respiration; that they are responsible for the contraction and relaxation of the muscles; that they assist in controlling the nerves; that they are, in a way, instrumental in releasing the energy locked up in food—the value of these elements becomes very evident, and their importance in the dietary inestimable. Some of the mineral salts are more widely distributed in food than others, and the danger arising from their deficiency in the diet is not so great as is the case with others; hence attention is called to those found by investigators to be most often lacking or deficient in the average diet; i.e., calcium, phosphorus, and iron. A brief summary of the special parts played by these elements will be outlined here.

Calcium.—Physiology teaches that about eighty-five per cent. of the mineral matter of the bone, or at least three-quarters of the ash of the entire body, consists of calcium phosphates. It has long been known that this mineral salt is necessary for the coagulation of the blood, and science has demonstrated that “the alternate contractions and relaxations which constitute the normal beating of the heart are dependent, at least in part, upon the presence of a sufficient, but not excessive concentration of calcium salts in the fluid which bathes the heart muscles.”[10]

Phosphorus.—According to Sherman, phosphorus compounds are as widely distributed in the body, and as strictly essential to every living cell as are proteins. Science has also proved that they are important constituents in the skeleton, in milk, in glandular tissue, in sexual elements, and in the nervous system; that these compounds take part in the functions of cell multiplication, in the activation and control of enzyme actions, in the maintenance of neutrality in the body; that they exert an influence on the osmotic pressure and surface tension of the body, and upon the processes of absorption and secretion. Like calcium, phosphorus is absolutely essential to the growth and development of the body, and, as in the case of the mineral, its presence in the dietary must be accorded strict attention, in order to avoid the results accruing from its deficiency. Casein, or caseinogen of milk and egg yolk (ovovitellin), are the substances richest in this mineral salt. The fact that the phosphorus existing in grains (cereals) may be removed largely in the process of milling, makes it advisable to consider the use of the breads made from the whole grains.

Iron.—The presence of iron as an essential constituent of hemoglobin has already been discussed. That which is not in the hemoglobin is chiefly found in the chromatin substances of the cells.

The body does not keep a reserve store of iron on hand as is the case with calcium and phosphorus in the bone tissues, but must depend upon the daily intake in food to supply its needs. The iron content of food materials is not large, but a careful regulation of the iron bearing foods (see Table on page 5) will make it easy to cover the demands of the body with a material which has been found to do its work most efficiently. Medicinal iron has received much attention in the determination of the essential needs of the body. “Whether medicinal iron actually serves as material for the construction of hemoglobin is not positively known, but we have what appears to be a good evidence that food iron is assimilated and used for growth and for regeneration of the hemoglobin to much better advantage than are inorganic or synthetic forms, and that when medicinal iron increases the production of hemoglobin, its effect is more beneficial in proportion as food iron is more abundant—a strong indication that the medicinal iron acts by stimulation rather than as material for the construction of hemoglobin” (Sherman).

The newborn infant has a store of iron already on hand, derived from the mother through the placenta before birth. After the birth, and through the nursing period, the child receives a certain amount of iron from the mother’s milk. This supply is not altogether reliable, however, since any disturbance of the digestion will tend to interfere with its absorption, and consequently deprive the organism of what would otherwise be used for the building up of the blood supply. Thus it is clearly indicated that the infant’s safest source of iron is from the mother during the pre-natal period. This supply must necessarily come from her diet during this time, and is made possible by regulating day by day the iron bearing foods in her dietary. After the original store of iron is reduced to that of the adult (after the child has tripled in birth-weight, generally at 12 or 13 months), and during the remainder of the growth period, it is very necessary to regulate the iron-bearing food in the diet, in order to insure the child of an adequate amount to cover the demands made by the increasing blood supply.

VITAMINES

Up to a few years ago it was believed a complete diet should contain an adequate amount of protein of a proper type, a sufficient amount of calcium, phosphorus and iron, and enough carbohydrates and fats to furnish the body with sufficient fuel to cover its energy expenditures. This belief was proved to be incorrect a number of years ago by Dr. Hopkins of England. In making certain feeding experiments with rats, Dr. Hopkins showed that some substance or substances present in milk, other than those already mentioned, was essential for the growth of the animal; that animals deprived of this material grew for a time, but gradually ceased to do so. Later on, Osborne, Mendel, McCollum and Davis discovered a like substance in butter fat; and still later Dr. McCollum found the same growth stimulating material, or one very like it, existing in the leaves of plants. These scientists found, upon investigation, that there were probably two substances in milk—one soluble in the fat, the other in the protein-free and fat-free whey—both of which were essential for normal growth. In 1911 Dr. Funk discovered in rice polishings a substance which he believed to be a cure and preventive of Beri-beri; to this substance, which is now believed to be identical with the second substance found in milk, he gave the name “vitamine.” Dr. Funk’s name “Vitamine” is now accepted to cover a number of substances essential to growth, and for the prevention and cure of certain diseases. To the first two has been added a third member of the vitamine family, which has proved to be a cure and preventive of scurvy. These substances are called—on account of the substances in which they are soluble—“Fat soluble A,” “Water soluble B,” and “Water soluble C.” The table on page 496 shows the sources from which these factors may be obtained. The four plus system is used by Dr. Eddy to describe the abundance with which they occur.[11]

Function of “Fat Soluble A.”—All investigators agree that the “A” vitamine is an essential factor in the growth of young tissue, and the repair of mature tissues. McCollum claims that this vitamine is likewise a factor in the prevention of the eye disease known as xerophthalmia, and other scientists also hold this opinion. Eddy states that a diet lacking in the “A” vitamine will, in the majority of cases, result in stunted growth and the development of the eye disease, and that the appearance of the latter may be taken as a sure indication of the absence or deficiency of this vitamine.

The following diagram shows the effect of adding fat soluble “A” to the diet which was adequate in other respects. This chart represents the growth curve of young rats.[12]

Figure showing the effect upon growth of adding “fat soluble A”
to a diet adequate in all other respects.
Courtesy of Dr. E. V. McCollum.

Mellanby of England believes the “A” vitamine to be a factor in the prevention of rickets. Scientists of America have recently investigated this disease, and Dr. Hess (New York) has found cod liver oil to be a remedy for it. Cod liver oil is known to be rich in “Fat soluble A,” but whether the cure of rickets is due to the presence of this vitamine in the oil, or to a possible fourth vitamine, is still undetermined.

Effect of Heat on the “A” Vitamine.—Heat, as applied in the ordinary methods of cooking, is not believed to exert a great deal of destruction upon the “A” type of vitamine; but hydrogenation, the process used in the hardening of certain fats in the manufacture of lard substitutes, is said to destroy it completely.

“Water Soluble B.”—The second vitamine discovered in milk and believed to be identical with the Funk vitamine is more widely distributed than the “A” vitamine. For this reason it is not so likely to be deficient in the diet as is found to be the case with the “A.” A glance at the table shows that the best sources outside of yeast are the seeds of plants and the milk and eggs of animals. In beans and peas the “B” vitamine is distributed throughout the entire seed, but in the cereal grains it is found chiefly in the embryo. As a result, bread made from fine white flour or meal is much more apt to be deficient in vitamine of the “B” type than that which is made from the whole grain; the same is true of rice and other cereals. Spinach, potatoes, carrots and turnips show an appreciable amount of the vitamine, but beets are known to be extremely poor in it. Nuts too are considered a valuable source.

Function of the “B” Vitamine.—Like the “A” vitamine, water soluble “B” is believed to be essential to growth. Funk established its value as a preventive and cure of Beri-beri, the disease common in the Orient among people living largely upon a diet of polished rice and fish. Besides being a growth-stimulating substance and an antineuritic, the “B” vitamine is highly valued for its stimulating effect upon the appetite. To this property is probably due at least part of the credit for which certain substances work for the promotion of growth in animals. This can be utilized to good advantage for children showing a disposition to refuse food, by supplementing formulas made from milk,[13] with the expressed juice of vegetables and fruits known to be rich in the “B” vitamine.

Effect of Heat on the “B” Vitamine.—This vitamine also shows a resistance to heat; that is, as applied in the methods generally used in cooking, pasteurization temperatures do not materially affect the vitamine property of the formula as far as the “A” and “B” factors are concerned.

The Effect of Alkali (Soda) upon the “B” Vitamine.—It has been an ordinary practice to add soda to the water in which certain vegetables are cooked, for the ostensible purpose of softening the vegetables and hastening their cooking. The practice has been condemned by many scientists who are making experiments along these lines, on account of its destructive power upon the “B” vitamine. Chick and Hume in England claim that when the amount of food given contains originally just sufficient vitamines to cover the growth factor the use of soda in the cooking water does serious harm to these vitamines. This is a point well worth remembering. It is often difficult to persuade certain individuals to eat vegetables in appreciable quantities; if the vitamines were reduced though the method of preparing the food, these individuals would not obtain a sufficient quantity of the vitamines. “Water Soluble C.”—The third member of the vitamine family is known for its antiscorbutic property; that is, it is the best known cure and preventive of scurvy. It likewise exerts a certain amount of influence upon the growth of the animal and must be present in the diet, in order that the health and well-being of the individual may be safeguarded. The “C” vitamine, like the “B” vitamine, is soluble in water, and is present to an appreciable extent in the fresh juices of the fruits and vegetables. Some are richer in this respect than others (orange and tomato juice), while the cereals, grains, seed of plants, sugars, oils, and meats are singularly deficient. Milk (whole) does not contain a great amount of the “C” vitamine, and this amount is still further reduced under certain methods of preparation. Milk powders, made either from the whole or the skimmed milk, are found to contain only very small amounts of this essential substance. Condensed milk and cream are supposed to be free of “C,” and the same is true of eggs.

Effect of Heat on “C” Vitamine.—All authorities agree that the “C” vitamine is much more sensitive to heat than the other two; and for this reason much of the value obtained from this vitamine in uncooked material may be lost when the food containing it is subjected to long-continued heat. Hess claims that the temperature used for pasteurizing milk for some time, is more destructive to this vitamine than boiling water temperature continued for a few minutes only.[14] There is need for care in formulating the diet for children to see that they are given fresh fruit every day; or when that is not possible, to see that they are at least given tomato juice. This substance is rich in the antiscorbutic vitamine, and according to experiments made by Sherman, LeMer and Campbell, loses fifty per cent. of its antiscorbutic power when boiled one hour. Dr. Delf at the Lister Institute experimented with raw and cooked cabbage, and found that when this material was cooked for one hour at temperatures ranging from 80° to 90° C the loss in antiscorbutic power amounted to 90% in the cooked leaves over the raw material. Dr. Delf also concluded from her experiments that it was advisable to add neither acid nor alkali in the cooking of vegetables if these substances were to give their maximum value of vitamines.

From the foregoing description of these vitamine factors, it is readily seen why so many dietaries are deficient in these essential substances. The limited sources from which to obtain the “A” vitamine; the sensitiveness of the “B” vitamine to the action of alkalies; the sensitiveness of the “C” vitamine to heat, alkali and acid, moreover the limitation of its presence chiefly to the fresh fruits and plant juices,—all point to the need of special care in the selection of the food materials and of the manner in which these materials are prepared for consumption.

SUMMARY

In the descriptions just given of the various foodstuffs, especially in regard to their function in the body, it is readily seen that no one foodstuff is used to the exclusion of another. It is further seen that in the upkeep of the body, which includes not only the building and repairing of its tissues, but the running of the engine and maintaining of its normal temperature, the organism uses each and all of the organic food substances for the production of heat. Furthermore, while the tissues are chiefly built from protein material, and physiology teaches that protein can be built only from other protein, these tissues contain a certain amount of carbohydrate, fat, mineral salts, and water; this furnishes distinct evidence that the building of the cells and tissues of the body cannot be accomplished by means of protein alone, but by the judicious balancing of all the foodstuffs in the dietary. Science has gone even further than this, as has just been demonstrated, and has proven that without the substances known as vitamines the normal growth and development in the young would be arrested, and that the maintenance of the adult body would be impaired. It has also proven that certain diseases owe their development to deficiencies in the vitamine supply to the body.

PROBLEMS