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 meansof 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, inorder 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 page5) 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 anydisturbance 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.

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. In1911 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 page496shows 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]

Without fat soluble A, weight stays more or less constant; with fat soluble A, weight increases on a steep curve

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 (NewYork) 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 cookedcabbage, 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.

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.

(a) Outline briefly what is believed to be the essentials of an adequate dietary.(b) List the fuel foods and show their most economical source.(c) List the best sources of the complete proteins.(d) Show how the incomplete protein foods may be made adequate for growth.

(a) Outline briefly what is believed to be the essentials of an adequate dietary.

(b) List the fuel foods and show their most economical source.

(d) Show how the incomplete protein foods may be made adequate for growth.

FOOTNOTES:[1]One quart of milk contains more calcium than a quart of clear saturated solution of lime water.[2]For complete list, seeEddy’s Table, in Appendix.[3]“Chemistry of Food and Nutrition” (revised edition), by Sherman.[4]Scientists are proving the need for certain vitamine factors in the diet in order that the growth and development of young tissues and the repair of adult tissues may proceed. The part played by these substances will be discussed later.[5]“Chemistry of Food and Nutrition” (2d ed.), by Sherman.[6]“The Basis of Nutrition,” by Graham Lusk.[7]“Food Products,” by Henry Sherman.[8]Abstracts made from thirteen papers from the Laboratory of Physiological Chemistry, Jefferson Medical College, Philadelphia; published in the “American Journal of Physiology and Science,” by Minna C. Denton. U.S. Department of Agriculture.[9]“Chemistry of Food and Nutrition” (revised), p. 333, by Henry Sherman.[10]“Chemistry of Food and Nutrition” (revised edition), by Sherman.[11]“The Vitamine Manual,” p. 64, by Walter Eddy[12]Courtesy of Dr. E. V. McCollum.[13]Milk from cows whose diet has been deficient in vitamines shows a like deficiency in vitamine content—the same is true of mother’s milk.[14]“The Vitamine Manual,” p. 64, by Walter H. Eddy.

[1]One quart of milk contains more calcium than a quart of clear saturated solution of lime water.

[2]For complete list, seeEddy’s Table, in Appendix.

[3]“Chemistry of Food and Nutrition” (revised edition), by Sherman.

[4]Scientists are proving the need for certain vitamine factors in the diet in order that the growth and development of young tissues and the repair of adult tissues may proceed. The part played by these substances will be discussed later.

[5]“Chemistry of Food and Nutrition” (2d ed.), by Sherman.

[6]“The Basis of Nutrition,” by Graham Lusk.

[7]“Food Products,” by Henry Sherman.

[8]Abstracts made from thirteen papers from the Laboratory of Physiological Chemistry, Jefferson Medical College, Philadelphia; published in the “American Journal of Physiology and Science,” by Minna C. Denton. U.S. Department of Agriculture.

[9]“Chemistry of Food and Nutrition” (revised), p. 333, by Henry Sherman.

[10]“Chemistry of Food and Nutrition” (revised edition), by Sherman.

[11]“The Vitamine Manual,” p. 64, by Walter Eddy

[12]Courtesy of Dr. E. V. McCollum.

[13]Milk from cows whose diet has been deficient in vitamines shows a like deficiency in vitamine content—the same is true of mother’s milk.

[14]“The Vitamine Manual,” p. 64, by Walter H. Eddy.

Science has proved that the human body is composed of certain chemical elements and that food materials are combinations of like elements; it has likewise proved that the body will utilize her own structure for fuel to carry on the work of her various functions unless material is supplied for this purpose from an outside source, namely, food, which in chemical composition so closely resembles that of the human body.

Amount and Type of Food.—The next point of investigation would logically be the amount and kind of food necessary to best accomplish this purpose. To be able to do this it was necessary to have some standard unit by which to measure the amount of heat each food was capable of producing when burned outside the body, after which it was more or less simple to calculate the heat production of each of the food combinations within the organism. An apparatus known as the “Bomb Calorimeter”[15]was devised by Berthelot, and adapted for the examination of food materials by Atwater and Blakesley. The food material to be tested was placed within the bomb, which was charged with a known amount of pure oxygen. The bomb was then sealed and immersed in a weighed amount of pure water, into which a very delicate thermometer was inserted. The food within the bomb was ignited by means of an electric fuse, and the heat given off by the burning of the material was communicated to the surrounding water andwas registered upon the thermometer. It was evident that some definite name had to be devised by which these heat units might be known. Hence the name “calorie,” which representsthe amount of heat required to raise the temperature of 1 kilogram of pure water 1 degree centigrade, or about 4 pounds of water 1 degree Fahrenheit.

Transformation of Foods into Available Fuel.—A comparison has been made between the human body and steam engine, but this comparison is not adequate, since the food does not produce heat within the body originally, but energy of which heat is a by-product. Each food combination has a certain amount of dormant energy within its structure and this energy does not become active nor can it be utilized by the body until the food, of which it is a part, is changed within the organism to substances more nearly like its own. This liberated active energy is then used as a motive power to carry on the internal and external work of the body, and the heat, which is invariably the consequence of any active energy (motion), leaves the body as such. It will be seen, then, that the human body acts not as a steam engine, but rather as atransforming machineby means of which the dormant energy of the food is transformed into an active agent of which heat is a natural result.

In the calorimeter it was found that the carbohydrates and fats burned to the same end products, namely, carbon dioxide and water, while the proteins, upon oxidation, produced carbon dioxide, water and nitrogen gas. In the body it was found that the carbohydrates and the fats acted in exactly the same manner as in the calorimeter, producing the same end products. But this was not the case with the proteins; the oxidation process of this chemical combination was found to be not nearly so complete within the body as in the calorimeter, and instead of the free nitrogen as produced in the apparatus there were urea and othernitrogenous substances eliminated which, while combustible, represented a less complete oxidation of the proteins.

The following table represents the amount of heat produced as the result of a complete oxidation of the foodstuffs in the calorimeter.

TABLE[16]

Carbohydrates4.10cal. per gramFats9.45 cal. per gramProtein (nitrogen × 6.25)5.65 cal. per gram

The loss of potential energy due to the incomplete oxidation of the proteins in the body is approximately 1.3 calories to each gram of protein in food; consequently in calculating the fuel value of protein foods, due allowance must be made for these losses. Allowance must also be made for the incomplete digestion, or losses occurring in the digestion, of the foodstuffs. These losses, as well as the approximate amount of each constituent absorbed, are represented in the following table.[17]

LostAbsorbedCarbohydrates2 per cent.98 per cent.Fats5 per cent.95 per cent.Proteins8 per cent.92 per cent.

The physiological fuel factors of food, or the amount of heat produced as the result of combustion of 1 gram of organic food material after the above-mentioned losses have been accounted for, may be obtained as follows.[18]

Carbohydrates4.10× 98% = 4 cal. per gramFats9.45 × 95% = 9 cal. per gramProteins4.35 × 92% = 4 cal. per gram

In primeval days, when man led a more natural life, his very existence depended upon his ability to wrest from the earth his 4—9—4; these, then, constitute what are known as the “physiological fuel factors” of carbohydrates, fats, and proteins respectively.

Determination of Fuel Value of Food.—In determining the amount of heat produced by a given amount of food, it is first essential to reduce the amount to grams (for example, 1 lb. equals 480 grams): first, because the gram is a unit of weight commonly used in dietetic calculations; second, because the fuel factors are based on the amount of heat produced by the burning of one gram of organic foodstuffs. Knowing the composition of food, that is the number of hundredths of protein, carbohydrate and fat it contains, it is a simple matter to estimate its fuel value by multiplying the amount of each contained in one gram by its physiological fuel factor 4.4.9. Thus if the composition of a food is 3-3/10% protein, 4% fat and 5% carbohydrate, one gram would contain .033 gram of protein, .04 gram of fat and 0.5 gram of carbohydrate. Hence one gram of milk would produce

.033 × 4=.132 calorie from protein.040× 9=.360calorie from fat.050× 4=.200calorie from carbohydrateor.692 calorie in all

But it is not necessary to estimate the fuel value of so small a quantity as one gram, and, since the value of protein, carbohydrates and fats is always the same it is more satisfactory to estimate the amount of the organic constituents contained in the entire given quantity of food, rather than stopping to figure out the fuel value of the small quantity.

This is done by multiplying the entire number of grams of food given by the amount of protein, fat andcarbohydrate contained in one gram, then multiplying these results by the physiological fuel factor of each. Thus 100 grams of milk would yield

100 × .033=3.3 × 4=13.2 calories from protein100 × .040=4.0 × 9=36.0 calories from fat100 × .050=5.0 × 4=20.0 calories from carbohydratesor a total of69.2 calories from 100 grams of milk.

The Standard or 100 Calorie Portion.—Just as it has been more convenient to estimate a larger rather than a smaller quantity of food material, so it is frequently more desirable to estimate a hundred calories, rather than one calorie. This is especially useful when dietaries of high caloric (fuel) value are to be estimated, or dietaries in which foods of like composition and fuel value are to be interchangeable. In such cases it is a simple matter to select the desired number of 100 calorie portions of those foods which are to make up the dietary.[19]

Method of Estimating the 100 Calorie Portion.—The number of calories yielded by 100 grams of food material is taken as a basis upon which to estimate the 100 calorie portion, and X represents the number of grams required to yield this portion. The problem is one of “simple proportion,” for example, take the 100 grams of milk just estimated, we found that 100 grams (or c.c.) furnished 69.2 calories of heat, then, 100:69.2 :: X:100—145; or 145 grams of milk are required to furnish 100 calories of heat. Suppose it is desirable to substitute eggs for a part of the milk in the diet, eggs have a higher fuel value per unit of weight than milk, their average composition being 13.4% protein, and 10.5% fat (no appreciable amount of carbohydrates), 100 grams of eggs would yield

100 × .134=13.4 × 4=53.6 calories from protein100 × .105=10.5 × 9=94.5 calories from fat,or a total of148 calories.

The Standard or 100 calorie portion of eggs would be,

100:148 :: X:100 = 68

or the number of grams required to yield 100 calories.

Thus it is seen that in using the fuel value of a hundred grams of food material for estimating the standard or 100 calories portion the extremes are always the same. Hence, the weight of the 100 calorie portion may always be obtained by multiplying the extremes and dividing the result by the number of calories furnished by 100 grams of food material.

(a) Compare the fuel value of the various common food materials.(b) How does the fuel value of a chicken salad compare with that of fruit salad?(c) Figure the fuel value of a cupful of cream of tomato soup and compare it with that furnished by the same quantity of beef broth.(d) Weigh and measure a 100-calorie portion of spinach and compare it with a 100-calorie portion of sweet potato.

(a) Compare the fuel value of the various common food materials.

(b) How does the fuel value of a chicken salad compare with that of fruit salad?

(c) Figure the fuel value of a cupful of cream of tomato soup and compare it with that furnished by the same quantity of beef broth.

(d) Weigh and measure a 100-calorie portion of spinach and compare it with a 100-calorie portion of sweet potato.

FOOTNOTES:[15]For full description and methods used, see “Journal of The American Chemical Society,” July, 1903.[16]“Chemistry of Food and Nutrition” (revised edition), by Sherman.[17]“Chemistry of Food and Nutrition,” by Sherman.[18]“Chemistry of Food and Nutrition” (revised), by Sherman.[19]SeeTable of Standard or 100 Calorie Portions, in Appendix.

[15]For full description and methods used, see “Journal of The American Chemical Society,” July, 1903.

[16]“Chemistry of Food and Nutrition” (revised edition), by Sherman.

[17]“Chemistry of Food and Nutrition,” by Sherman.

[18]“Chemistry of Food and Nutrition” (revised), by Sherman.

[19]SeeTable of Standard or 100 Calorie Portions, in Appendix.

The human body, as far as can be judged, does not use one nutrient to the exclusion of another, but science has proved that the best results are obtained from diets balanced to suit the needs of the body, providing the fuel and repair materials in the amounts which are calculated to give the maximum value with the minimum expenditure on the part of the organism.

For while no two individuals are exactly alike, there are factors which govern or influence the food requirements of all, and thus make it possible to estimate the needs of the body with a fair degree of accuracy.

It has been found, by means of calorimeter experiments (direct and indirect), that a certain amount of heat is produced within the body, regardless of external movement or food; that is, when a body is lying absolutely quiet with no movement save that of breathing, the internal work of the organism, which is continuous, releases so much heat, and this is produced whether there is food to replace it or whether the body structure is burned. This is known as thebasal rate of metabolism, and constitutes the normalbasal requirements. Any external movement will increase this rate; the greater the activity the higher the increase. Consequently external work calls for food in addition to that which is used to run the engine, in order to save the body from destruction.

DuBois[20]finds “Basal Metabolism above normal in exophthalmic goiter, in fevers, in lymphatic leukemia, andin pernicious anemia, in severe cardiac disease, and in some cases of severe diabetes and cancer; it is lower than normal in cretinism, and in myxedema, in old age, in some wasting diseases and perhaps in some cases of obesity.” This fluctuation in the Basal Rate of metabolism furnishes a factor in the diagnosis of disease, not only recognized but coming more and more in use.

For the Adult.—Muscular activity, Age and Size, are most important factors influencing the food requirements. The physical condition and environment of the individual also exert a certain amount of influence upon the intake of food.

Work.—Muscular activity, as already stated, increases the body expenditures; consequently the more active the work the greater amount of energy food needed per unit of weight.

Age.—As the individual grows older, the rate of metabolism decreases until, in old age, it is not more than a third to a fifth of what it was in earlier life. This is due to a general “slowing down” of the machinery, the heart does not beat so rapidly, nor is the respiration so quick. The digestive organs, the heart, the liver, and the kidneys, cannot handle the volume of food which was required during the period of greatest physical activity. Hence, any great excess over and above that which is needed for the maintenance of the body in health will be a source of danger to the elderly person. Von Noorden claims the food requirements of individuals from

60 to 70 years of age to be reduced 10%; for people from70 to 80 years of age to be reduced 20%; for people from80 to 90 years of age to be reduced 30%.

Sex.—Science has proved, that there is little difference in the food requirements of men and women, provided they are alike in age, weight and size, and are doing the same amount and type of work. But women, as a rule, weigh less than men, hence their food requirements are approximately less.

Murlin finds the food requirements of pregnant women to be some what higher than of non-pregnant ones, and the requirements of the nursing mother to be higher than either (see chapter onPregnancy and Lactation).

For the Child.—The factors influencing the food requirements are different, to a certain extent, from those of the adult. The main difference lies in the fact that the adult needs food only for the maintenance and repair of the body, while the child must have food, not only to cover its maintenance requirements, but to support the growth and development which should be continuous from birth to maturity. Resistance, too, must be developed during this period in order to safeguard the child through life.

The rate of metabolism in the infant is greater than at any other period of life, consequently, even if a child were one-third the weight of its parent, it would inevitably cease to grow and would become malnourished, if its food requirements were reckoned at only one-third that of the parent.

Adjusting the Food Requirements.—Taking these factors as guides for estimating the food requirements of man, it is evident that no hard and fast law can be laid down to cover all, that each individual must adjust the food intake according to the weight and activity of the body. Sherman has arranged the following table showing the energy expenditures per hour for the average man (154 pounds), per pound of body weight (these are approximate averages only).

TABLE[21]

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