COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD I'llllll " HX641 00723 QP1 41 .At92 1 91 0 Pnncip es of nutnt RECAP :^inciples of nutrition and nutritive ralue of food W. 0. Atwater C^P'^i I9i0 CoUegf of ^ijpgicians; anb burgeons ILihvavp Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/principlesofnutrOOatwa ^^ Issued March 1, 1902. U. S. DEPARTMENT OF AGRICULTURE. FARMERS' BULLETIN No. 142. PRINCIPLES OF NUTRITION AND NUTPJTIVE VALUE OF FOOD. (Corrected to April 20, 1910; reprinted without change, January, 1916.) W. O. AXWATER, Ph. E>., Special Agent in Oliarge of Nntrition Investigations, Office of Experiment Stations, PREPARKD UNDER THE SUPERVISION OF THE OFFICE OF EXPERIMENT STATIONS A. C. TRUE, Director. WAHIIINGTON GOVERNMENT PUINTINU OFFICE 1916 LEHER OF TRANSMITTAL. U. S. Department of Agriculture, Office of Experiment Stations, ^ Washington, D. C, April 5, 1906. Sir: I have the honor to transmit herewith an article on Principles of Nutrition anu Nutritive Value of Food, by Prof. W. O. Atwater, special agent in charge of nutrition investigations, prepared in accord- ance with instructions given by the Director of this Office. For a number of years the Department has carried on studies regarding the kinds and amounts of foods consumed by persons of different occupa- tions and with different incomes, the composition of food, the relative cost of nutrients when furnished by different foods, and many more technical questions. The present bulletin discusses the general prin- ciples of nutrition, as well as a number of the more important phases of the subject, with special reference to the results obtained in Depart- ment investigations and the closely related work of the agricultural experiment stations. As the work has progressed the earlier ideas have been modified, and the present bulletin is designed to supplement and replace earher Department publications by the author having a similar scope. In preparing this bulletin Professor Atwater has had the assistance of Miss Helen W. Atwater. The first edition of this bulletin was pubhshed several years ago. In preparing this edition for pubHcation a number of changes which seemed desirable have been made. It is beheved that the article is a useful summary of available infor- mation on the subject, and its publication as a Farmers' Bulletin is therefore recommended. Respectfully, A. C. True, Director. Hon. James Wilson, Secretary of Agriculture. 142 (2) CONTENTS. Page. Introduction 5 Chemical composition of the body and of food 5 Water 6 Mineral matter or ash 6 Protein : 6 Fats ; 7 Carbohydrates 7 Refuse 8 Food as building material and fuel 8 The body as a machine 8 Protein as building material 9 Protein as fuel for the body 10 Fats and carbohydrates as fuel 10 Value of food for supplying enei^ 10 Heat of combustion 11 The conservation of energy in the body 11 Fuel value 12 How the functions and nutritive value of food are learned 13 Food and food economy 14 Composition of common food materials 15 Proportions of nonnutrients in foods 18 Proportions of nutrients in foods 19 Digestion, assimilation, and excretion 20 Digestion 21 Absorption and assimilation 21 Excretion 22 Apparent and actual digestibility 22 Ease and quickness of digestion 23 Agreement of food with individuals 25 Proportions of digestible nutrients in food materials 25 Preparation of food — cooking 30 Dietaries and dietary standards 32 Methods of making dietary studies 32 American and European dietaries and dietary standards 34 Making home studies of dietaries 37 Adapting fo WATER. Water is one of the most abundant of these compounds. It forms over 60 per cent of the weight of the body of the average man, being a component part of all the tissues. It is thus an important constituent of our food, though it can not be burned, and hence does not yield energy to the body. MINERAL MATTER OR ASH. Other food ingredients which yield little or no energy and are yet indispensable to the body are the mineral matters. They form only 5 or 6 per cent of the body by weight, and are found chiefly in the bones and teeth, but are present also in the other tissues and in solution in the various fluids. When food or body material is burned the mineral constituents remain as ash. Phosphate of lime, or calcium phosphate, is the mineral basis of bone. Numerous compounds of potassium, sodium, magnesium, and iron are found in the body and are necessary to life. The remaining nutritive materials are organic compounds, so called because they occur principally in the organic, i. e., the animal and vegetable world. They all contain carbon, oxygen, and hydrogen, in varying proportions. Some also contain nitrogen, phosphorus, sul- phur, or other elements. Those occurring in the body and in food are divided into three principal groups — protein, fats, and carbohydrates. PROTEIN. This term includes the principal nitrogenous compounds. Protein' is familiar to us in the lean and gristle of meat, the white of eggs, the gluten of wheat, etc. It forms about 18 per cent, by weight, of the body of the average man. Protein compounds may be subdivided into albuminoids, gelatinoids, and extractives. The first group, the albu- minoids, include substances similar to the white of egg, the lean ot meat (myosin), the curd of milk (casein), and the gluten of wheat. The second group, the gelatinoids, '^ occur principally in the connective tissues, such as the collagen of the tendons and skin and the ossein of bone. The albuminoids and gelatinoids, classed together as proteids, are most important constituents of our food. They make the basis of bone, muscle, and other tissues, and are essential to the body structure. They are also used as fuel — that is, they are burned in the body to yield energy — and they are to some extent transformed into fat and stored in the body, but these are their less important uses. The pro- oThe term albuminoids is often applied to what are here called gelatinoids; the term proteid is used in the same significance; indeed, there is great confusion in the use of these terms by different writers. The terminology here followed is that recommended by the American Association of Agricultural Colleges and Experiment Stations. 142 tein compounds are most abundant in some of the animal foods, as lean meat, though the cereals contain them in considerable, and peas and beans in large, proportions. The gelatinoids are less valuable than the albuminoids for nutriment. The third class, the so-called extractives, are included with the pro- tein compounds because they contain nitrogen, but they differ greatly from the albuminoids and gelatinoids. They are the principal ingre- dients of meat extracts, beef tea, etc. They are believed to neither build tissue nor furnish energy, but to act as stimulants and appetizers. The craving wliich some persons have for meat is perhaps due in part to a desire for these extractives. The nitrogenous compounds of potatoes and other vegetable foods contain more or less of so-called amids, like asparagin, which are analogous to the extractives of meat, and like them can not build tissue, and hence have an inferior nutri- tive value. FATS. Fats occur chiefly in animal foods, as meats, fish, butter, etc. They are also abundant in some vegetable products, such as olives and cot- ton seed, from which they are expressed as oil, and occur in consider- able quantities in some cereals, notably oatmeal and maize (whole kernel), and in various nuts. In oiu- bodies and those of animals fats occur in masses under the skin and in other localities, and in minute particles scattered through the various tissues. The amount of fat in the body varies greatly with food, exercise, age, and other conditions. When more food is taken than is necessary for immediate use part of the surplus may be stored in the body. The protein and fat of food may thus become body protein and body fat; sugar and starch of food are changed to fat in the body and stored as such. When the food supply is short this reserve material is drawn upon for supple- mentary fuel. Fat forms about 15 per cent, by weight, of the body of an average man. Well-fed or overfed people with little muscular exercise often grow fat, but the tendency to fatness or leanness is more or less a question of personal idiosyncrasy or some other little understood factor, and not decided by food and exercise alone. CARBOHYDBATES. These include such compounds as starches, different kinds of sugar, and the fiber of plants or cellulose. They are found cliiefly in the vegetable foods, like cereal grains and potatoes; milk, however, con- tains considerable amounts of milk sugar, which is a carbohydrate. The carbohydrates form only a very small proportion of the body tissues — less than 1 per cent. Starches and sugars, which are very abundant in ortlinary food materials, are important food ingredients, bcrause they form an abundant source of energy and are easily digested. They may be and often are transformed into fat in the body. 142 REFUSE. Food, as we buy it at the market or even as it is served on the table, contains more or less of materials which we can not or do not eat, and which would have little or no nutritive value if we did eat them; such, for instance, as the bones of meat and fish, the shells of eggs, and the skins and seeds of fruits and vegetables. In discussing the chem- ical composition of foods such portions are usually counted as refuse, but they make an important item when we consider the actual cost of the nutrients of food. The materials grouped together as refuse contain, in part, the same ingredients as the edible portion, though usually in very different proportions. Thus bones are largely mineral matter, with some fat and protein ; eggshells are almost entirely min- eral matter; bran of wheat has a high content of fiber or woody mate- rial. Generally speaking, vegetable refuse is characterized by a high content of these latter constituents. In some cases material which is edible is classed as refuse because the flavor is objectionable. Thus peach and plum pits are too highly flavored to be agreeable if eaten in quantitjT^, and are commonly thought to be actually injurious. FOOD AS BUILDING MATERIAL AND FUEL. THE BODY AS A MACHINE. Blood and muscle, bone and tendon, brain and nerve — all the organs and tissues of the body — are built from the nutritive ingredients of food. With every motion of the body and with the exercise of feel- ing and thought as well, material is consumed and must be resupplied by food. In a sense, the body is a superior machine. Like other machines, it requires material to build up its several parts, to repair them as they are worn out, and to serve as fuel. In some ways it uses this material like a machine; in others it does not. The steam engine gets its power from fuel; the body does the same. In the one case coal or wood, in the other food, is the fuel. In both cases the energy which is latent in the fuel — the potential energy, as it is called in sci- entific language — is transformed into power and heat. From the time foods are taken into the body until they are digested, absorbed, utilized, and finally converted largely into the carbon dioxid and water vapor of the breath and the nitrogenous and other excretory products of the urine and feces, they undergo great chemical changes, very many of which liberate heat as a result of oxidation or some closely related process. It is through these complex chemical proc- esses that the body derives the energy for internal and external muscu- lar work. Heat is evolved by such chemical changes and also results from the muscular work of the body, and there is reason to believe that within wide limits the heat thus produced is sufficient for maintain- ing body temperature. The amount of heat produced in the body 9 must, or course, vary with the amount of food eaten, the work done, and other circumstances. However, the body is such a perfect piece of mechanism that the loss of heat by radiation, etc., is so adjusted to heat production that body temperature remains fairly constant. One important dijQPerence between the human machine and the steam engine is that the former is self-building, self-repairing, and self-regulating. Another is that the material of which the engine is built is verj different from that which it uses for fuel, but part of the material which serves the body as a source of energy also builds it up and keeps it in repair. Furthermore, the body can use its o^vn sub- stance for this purpose. This the steam engine can not do. The steam engine and the body are alike in that both convert the fuel into mechanical power and heat. They differ in that the body uses the same material for fuel as for building and also consumes its own mate- rial for fuel. In the use of its source of power the body is much more economical than any engine. But the body is more than a machine. It has not simply organs to build and keep in repair and supply with energy; it has a nervous organization; it has sensibilities; and there are the higher intellectual and spiritual faculties. The right exercise of these depends upon the right nutrition of the body. The chief uses of food, then, are two: (1) To form the material of the body and repair its wastes, and (2) to furnish muscular and other power for the work the body has to do and yield heat to keep the body warm. In forming the tissues and the fluids of the body the food serves for building and repair. In yielding power and heat it serves as fuel. If more food is eaten than is needed, more or less of the surplus may be and sometimes is stored in the body, chiefly in the form of fat. The fat in the body forms a sort of reserve supply of fuel and is utilized in the place of food. When the work is hard or the food supply is low the body draws upon this store of fat and grows lean. PROTEIN AS BUILDING MATERIAL. The principal tissue formers are the protein compounds, especially the albuminoids. These make the framework of the body. They build up and repair the nitrogeneous materials, as the muscles and ten- dons, and supply the albuminoids of the blood, milk, and other fluids. The albuminoids of food arc transformed into the albuminoids and gelatinoids of the body. Muscle, tendon and cartilage, bone and skin, the corpuscles of the blood, and the casein of milk are made of the albuminoids of food. The albuminoids are sometimes called "flesh formers" or "muscle formers," because the lean flesh, the muscle, is made from them, though the term is inadequate, as it leaves out of account the energy-furnishing function of protein. The gelatinoids of food, 8uch as the finer particles of tendon and the gelatin, which are 20565"— Bull. 142—16 2 10 dissolved out of bone and meat in soup, though somewhat similar to the albuminoids in composition, are not believed to be tissue formers; but they are valuable in protecting the albuminoids from consumption. That is, when the food contains gelatinoids in abundance less of albu- minoids is used. The proteids can be so changed in the body as to yield fats and car- bohydrates, and such changes actually occur to some extent. In this and other ways they supply the body with fuel. PROTEIN AS FUEL. FOR THE BODY. The protein compounds are not only used for building and repairing tissue, but are also burned directly in the body like the carbohydrates, and thus render important service as fuel. A dog can live on lean meat. He can convert its material into muscle and its energy into heat and muscular power. Man can do the same; but such a one- sided diet would not be best for the dog and it would be still worse for man. The natural food for carniverous animals, hke the dog, supplies fats and some carbohydrates, and that for omnivorous animals, like man, furnishes fats and carbohydrates in liberal amounts along with protein. Herbivorous animals, like horses, cattle, and sheep, naturally require large proportions of carbohydrates. FATS AND CARBOHYDRATES AS FUEL. Fats and carbohydrates are the chief fuel ingredients of food. Sugar and the starch of bread and potatoes are burned in the body to yield heat and power. The fats, such as the fat of meat and butter, serve the same purpose, only they are a more concentrated fuel than the carbohydrates. The body can also transform carbohydrates of food into fat. This fat, and with it that stored from the food, is kept in the body as reserve fuel in the most concentrated form. The different nutrients can to a greater or less extent do one another's work. If the body has not enough of one kind of fuel it can use another. But, while protein can be burned in the place of fats and carbohydrates, neither of the latter can take the place of the albumi- noids in building and repairing the tissues. • At the same time the gela- tinoids, fats, and carbohydrates, by being consumed themselves, pro- tect the albuminoids from consumption. VALUE OF FOOD FOR SUPPLYING ENERGY. Heat and muscular power are forms of force or energy. The energy latent in the food is developed as the food is consumed in the body. The process is more or less akin to that which takes place when coal is burned in the furnace of the locomotive. For the burning of the food in the body or the coal in the furnace, air is used to supply oxygen. 142 11 When the fuel is oxidized, be it meat or wood, bread or coal, the latent energy becomes active, or, in technical language, the potential energy becomes kinetic; it is transformed into power and heat. As various kinds of coal differ in the amoiuit of heat given off per ton, so various kinds of food and food ingredients give off different amounts of energy; that is, have different values as fuel in the body. HEAT OF COMBUSTION. The processes of oxidation of material and transformation of energy in the body are less simple than in the engine and less clearly under- stood. Late research, however, has given us ways of measuring the energy latent in coal, wood, and in food materials as well. This is most generally done in the chemical laboratory by an apparatus called the bomb calorimeter. The amount of heat given off in the oxidation 01 a given quantity of any material is called its "heat of combustion," and is taken as a measure of its latent or potential energy. The unit commonly used is the calorie, the amount of heat which would raise the temperature of 1 kilogram of water 1° C, or, what is nearly the same thing, 1 pound of water 4° F. Instead of this unit of heat a unit of mechanical energy may be used — for instance, the foot-ton, which represents the force required to raise 1 ton 1 foot. One calorie is equal to very nearly 1.54 foot-tons; that is to say, 1 calorie of heat, when transformed into mechanical power, would suffice to lift 1 ton 1.54 feet. THE CONSERVATION OF ENERGY IN THE BODY. The amounts of energy transformed in the body when food and its own material are burned within it are measured with the respiration calorimeter referred to on page 13. It is well known that the food is not completely oxidized in the body. These experiments have shown that the material which is oxidized yields the same amount of energy as it would if burned with oxygen outside the body, e. g., in the bomb calorimeter. The experiments show also that when a man does no muscular work (save, of course, the internal work of respiration, circu- lation, etc.), all the energy leaves his body as heat; but when he does muscular work, as in Ufting weights or driving a bicycle, part of the energy appears in the external work thus done, and the rest is given off from the body as heat. The most interesting result of all is that the energy given off from the body as heat when the man is at rest, or as heat and mechanical work together when he is working, exactly equals the latent energy of the material burned in the body. This is in accordance with the law of the conservation of energy. It thus appears that the body actually obeys, as we should expect it to obey, this great law which dominates the physical universe. 143 12 FTJEL. VALUE. We may make practical application of this principle of the conser- vation of energy in the body in measuring the actual value of food as fuel to the body, i. e., its " fuel value," by use of the bomb and respira- tion calorimeters. To do this we have to take into account the chem- ical composition of the food, the proportions of the nutrients actually digested and oxidized in the body, and the proportion of the whole latent energy of each which becomes active and useful to the body for warmth and work. Taldng our common food materials as they are used in ordinary diet, the following general estimate has been made for the energy furnished to the body by 1 gram or 1 pound of each of the classes of nutrients:'* Protein, fuel value, 4 calories per gram, or 1,820 calories per pound. Fats, fuel value, 9 calories per gram, or 4,040 calories per pound. Carbohydrates, fuel value, 4 calories per gram, or 1,820 calories per pound. It will be seen that when we compare the nutrients in respect to their fuel value, their capacities for yielding heat and mechanical power, a pound of protein of lean meat or albumen of egg is just about equiva- lent to a pound of sugar or starch, and a little over 2 pounds of either would be required to equal a pound of the fat of meat or butter or of body fat. The fuel value of food obviously depends upon the amounts of actual nutrients, and especially upon the amount of fat it contains. Thus a pound of wheat flour, which consists largely of starch, has an average fuel value of about 1,625 calories, and a pound of butter, which is mostly fat, about 3,410 calories. These are only about one-eighth water. Whole milk, which is seven-eighths water, has an average fuel value of 310 calories per pound; cream, which has more fat and less water, 865 calories, and skim milk, which is whole milk af"ter the cream has been removed, 165 calories. This high fuel value of fat explains the economy of nature in storing fat in the body for use in case of need. Fat is the most concentrated form of body fuel. We have been considering food as a source of heat and muscular power. There is no doubt that intellectual activity, also, is somehow dependent upon the consumption of material which the brain has obtained from the food; but just what substances are consumed to produce brain and nerve force, and how much of each is required for a given quantity of intellectual labor, are questions which the physio- logical chemist has not yet answered. o These estimates are based upon the latest and most reliable research and take into account only the material which is digested and oxidized so that its energy is actually available to the body. EarHer estimates, based on less accurate data and not making allowance for the amounts of fats and carbohydrates which escape oxidation in the body, give 4.1 calories per gram, or 1,860 calories per pound, for protein and carbohydrates and 9.3 calories per gram, or 4,220 for fats, figures which have come into common use. I 13 HOW THE FUNCTIONS AND NUTEITIVE VALUE OF FOOD ARE LEARNED. The principles above explained are based upon a great deal of experimenting and observation. The experimenting is of many kinds, but of especial importance is the work with the respiration apparatus and respiration calorimeter. Various forms of respiration apparatus have been devised within the last fifty years. Among the most important are those invented bv Pettenkofer and Voit in Munich. They consist of metal-walled chambers large enough for the subject (sometimes a man, sometimes a dog, sheep, or other animal) to live in comfortably for several days, and are furnished with devices for pumping air through and measur- ing and analyzing it as it enters and leaves the chamber. With such an apparatus it is possible not only to measure all the food and excreta, but also the materials given off from the lungs in the breath, and to make accurate determinations of the matter entering and leav- ing the body. A still more elaborate apparatus, by which not only all the matter passing in and out of the body may be measured, but also all the heat given off from it, is called a respiration calorimeter — that is, a machine for measuring both the respiratory products and the heat given off by the body. It is like the respiration apparatus, except that it is fur- nished with devices for measuring temperatures. Several have been built in Europe within the last twenty years, among the most success- ful being those by Rubncr and Rosenthal. °' Investigations in coop- eration with the United States Department of Agriculture are now being carried on in one recently built by the author and Professor Rosa at Wesleyan University.'' Its main feature is a copper-walled chamber 7 feet long, 4 feet wide, and 6 feet 4 inches high. This is fitted with devices for maintaining and measuring a ventilating cur- rent of air, for sampling and analyzing this air, for removing and measuring the heat given off within the chamber, and for passing food and other articles in and out. It is furnished with a folding bed, chair, and table, with scales and with appliances for muscular work, and has telephone connection with the outside. Here the subject stays for a period of from three to twelve days, during which time care- ful analyses and measurements are made of all material which enters the body in the food and of that which leaves it in the breath and excreta. Record is also kept of the energy given off from the body as heat and muscular work. The differences between the material taken into and that given 2.1 1.5 49.7 1.3 53. 2 1.5 63.3 1.5 69.7 1.7 70. 5 2.9 73.1 2.1 3.5 1.7 .7 .9 .9 .8 .7 .4 .8 1.2 . 5 1.1 2.9 1.0 3.4 2.1 .4 2.1 1.1 .9 .0 .0 n Uefu.se, shell. 6 Plain confectionery not containing nuts, fruit, or chocolate. «8iich vegetables as potatoes, squash, beets, etc., have ii f;<'rtain amount of inedible material, skin, iteedH, t'U;. The amount varies with the method of pr(f)arinK the vegetables, and can not be accu- rately estimated. The flgurcs given for refuse of vcgetalil(!H, fruits, etc., are assumed to represent approximately the amount of refuM In these foods as ordinarily prepared. 20555'' Bull. 1-12-16—^3 18 Table I. — Average composition of common American food products — Continued. Food materials (as purchased). VEGETABLE FOOD — continued. Fruits, berries, etc., fresh: a Apples Bananas Grapes Lemons Muskmelons Oranges Pears Persimmons, edible portion Raspberries Strawberries ^ Watermelons Fruits, dried: Apples Apricots Dates Figs Raisins Nuts: Almonds Brazil nuts Butternuts Chestnuts, fresh Chestnuts, dried Cocoanuts Cocoanut, prepared Filberts Hickory nuts Pecans, polished Peanuts Pinon (Pinus edulis) Walnuts, black Walnuts, English Miscellaneous: Chocolate Cocoa, powdered Cereal coffee, infusion (1 part boiled in 20 parts water) c Refuse. Per ct. 25.0 35.0 25.0 30.0 60.0 27.0 10.0 5.0 59.4 10.0 "io.'o Per ct. 63.3 48.9 58.0 62.5 44.8 63.4 76.0 66.1 85.8 85.9 37.5 28.1 29.4 13.8 18.8 13.1 2.7 2.6 .6 37.8 4.5 7.2 3.5 1.8 1.4 1.4 6.9 2.0 .6 1.0 5.9 4.6 Pro- tein. Per ct. 0.3 .8 1.0 .7 .3 .6 .5 .8 1.0 .9 .2 1.6 4.7 1.9 4.3 2.3 11.5 8.6 3.8 5.2 8.1 2.9 6.3 7.5 6.8 5.2 19.5 8.7 7.2 6.9 12.9 21.6 Fat. Per ct. 0.3 .4 1.2 .5 .6 .1 2.2 1.0 2.5 .3 3.0 30.2 33.7 8.3 4.5 5.3 25.9 67.4 31.3 25.5 33.3 29.1 36.8 14.6 26.6 48.7 28.9 Carbo- hy- drates. Ash. Per ct. 10.8 14.3 14.4 6.9 4.6 8.5 12.7 31.5 12.6 7.0 2.7 66.1 62.6 70.6 74.2 68.5 9.6 3.5 .5 35.4 56.4 14.3 31.6 6.2 4.3 6.2 18.5 10.2 3.0 6.8 30.3 37.7 Per ct. 0.3 .6 .4 .4 .3 .4 .4 .9 .6 .6 .1 2.0 2.4 1.2 2.4 3.1 1.1 2.0 .4 1.1 1.7 .9 1.3 1.1 .8 .7 1.6 1.7 .6 .6 2.2 7.2 Fuel value per pound Calo- ries. 190 260 295 125 80 150 230 550 220 150 50 1,185 1,125 1,276 1,280 1,265 1,515 1,485 . 385 916 1,386 1,296 2,865 1,430 1,146 1,466 1,775 1,730 730 1,260 2,625 2,160 o Fruits contain a certain proportion of inedible materials, as skin, seeds, etc., which are properly classed as refuse. In some fruits, as oranges and prunes, the amount rejected in eating is practically the same as refuse. In others, as apples and pears, more or less of the edible material is ordinarily rejected with the sMn and seeds and other inedible portions. The edible material which is thus thrown away, and should properly be classed with the waste, is here classed with the refuse. The figures for refuse here given represent, as nearly as can be ascertained, the quantities ordinarily rejected. b Milk and shell. c The average of five analyses of cereal coffee grain is: Water 6.2, protein 13.3, fat 3.4, carbohydrates 72.6, and ash 4.5 per cent. Only a portion of the nutrients, however, enter into the infusion. The average in the table represents the available nutrients in the beverage. Infusions of genuine coffee and of tea like the above contain practically no nutrients. PROPORTIONS OF NONNTJTRIENTS IN FOODS. It will be interesting to note some of the differences in food mate- rials as shown by their composition. One of the first things which may be observed when a table like the above is studied, is the differ- ences in the proportions of nonnutrients, i. e., refuse and water. Many kinds of food as they are purchased contain large amounts of refuse, as the skin and bones of meat and fish, the skin or rind and seeds of vegetables, etc, which necessarily lessen the proportion of nutrients. While such refuse is found in meats, fish, eggs, fresh vege- tables, and fruits, it is usually absent in the dairy products (milk, but- ter, cheese, etc.), dried vegetables, cereal foods (flour, breakfast foods, etc.), and the bread, cakes, and other foods prepared from them. In considering the edible portion we find that the amount of water present 142 19 also affects the nutritive value of food. Water is necessary to the body, and it is usually supplied in abundance by beverages, although the amount contained in the solid food consumed in a day is quite considerable. Water forms from 40 to 50 per cent of the ordinary cuts of meat; it is especially abundant in the flesh of lean animals, and tends to decrease as fat increases, and vice versa. It is even more abundant in fresh fish than in meats, but in dried fish there is of course comparatively little. Fresh vegetables and fruits contain sometimes as much as 80 or 90 per cent or more of water, while dried seeds and the food materials prepared from them (beans, peas, meals, flour, cereal breakfast foods, etc.) usually contain, roughly speaking, from 10 to 12 per cent of water. Many cooked foods contain more water than the raw materials from which they are made, owing to the quantities added in cooking. Thus some thin soups are little more than flavored and colored water, and of course have an extremely low nutritive value. In other cooked foods, notably meat, which have been baked, roasted, or fried, the amount of water is diminished by cooking. PROPORTIONS OF NUTRIENTS IN FOODS. The most important of the actual nutrients has been seen to be pro- tein. This occurs most abundantly in animal foods— =-meat, fish, eggs, and dairy products, and in the dried legumes, as beans and peas. Butter and lard are exceptions to this statement, as they represent the fat of milk and meat. The proportion of protein present in meats and fish varies greatly with the kind and cut. In beef, veal, and mut- ton it composes between 14 and 26 per cent of the edible portion. It is generally less abundant in the flesh of fish, because the latter is more watery than meat. The fatter the meat the smaller is the pro- portion of protein; lean pork has less than beef and mutton, and fat pork almost none. It is more abundant in cheese (28-38 per cent) and likewise in dried beans and peas (18-25 per cent). Protein makes up, roughly speaking, from 7 to 15 per cent of the cereals, being least abundant in rye and buckwheat and most abundant in oats. Wheat flour averages not far from 1 1 per cent and bread not far from 9 per cent of protein. Fresh vegetables and fruits contain almost no pro- tein, seldom if ever more than 5 and often only 1 per cent or less. The chief sources of fat in ordinary diet are the animal foods, though some fat is derived from vegetable foods. The quantities present in meats vary considerably, ranging from less than 10 per cent in some cuts of beef and veal to over 40 per cent in a side of pork and over 80 per cent in fat salt pork. The leaner fish, like cod and haddock, usually cojitain almost none, but in the fatter kind, like shad, mack- erel, and notably salmon, there is often from 5 to 10 per cent and some- tiriicH as iriiich as 15 per cent of fat. The chemical composition of 20 salmon is not unlike that of lean meat. In both meat and fish the increase of fat usually means a decrease in the proportion of water, as was stated above. Milk averages about 4 per cent of fat. Butter is, as we have seen, nearly pure fat, and whole milk cheese may.have any- where from 25 to 40 per cent of fat, according to the richness of the cream or milk from which it is made. The olive and the cotton seed are rich in fat, large quantities of them being used annually for the production of oils. Most of our common edible nuts also contain considerable fat. With the exception of oat- meal, which contains about 7 per cent, there is comparatively little fat in the cereals in the form in which they are ordinarily purchased, or in the dried legumes, while in the green vegetables and most fruits it is practically wanting. The carbohydrates, unhke the fats, are almost entirely absent from the animal foods, except milk, but form the most important nutrient of most vegetable foods. Some glycogen (a carbohydrate) is found in the liver and in other animal tissues. The carbohydrates make up from 70 to 80 per cent of the cereals, 60 to 70 per cent of the dried legumes, and the bulk of the nutrients of fresh vegetables and fruits. The nutrients of sugar, molasses, honey, etc., are, of course, almost entirely carbohydrates. Mineral matters occur in all the ordinary articles of food. Fresh meats and fish contain not far from 1 per cent, although in fat, unsalted pork the quantity may be as small as 0.1 per cent. Milk contains about 0.7 per cent mineral matters. In the cereals the proportion ranges from about 0.3 to over 2 per cent, while in green vegetables and fruits it is usually less than 1 per cent. The dried legumes con- tain from 3 to 4 per cent of mineral matters. In brief, then, it may be said that meats, fish, eggs, milk, fresh vegetables, and fruits contain the most refuse and water; that protein is most abundant in the animal foods and in the legumes and occurs in considerable quantities in the cereals; that fats occur principally in the animal foods ; that carbohydrates are found almost exclusively in the vegetable products and milk ; and that small quantities of mineral matters are found in all food materials. The fuel value varies within wide limits, being greatest in those materials which contain the most fat and the least water. DIGESTION, ASSIMILATION, AND EXCRETION. ' ' We live not upon what we eat, but upon what we digest." Food as we buy it in the market, or even as we eat it, is not usually in condition to be made into body structure or used as body fuel. It must first go through a series of chemical changes by what is called digestion, which prepare it to be absorbed, taken into the blood and lymph, and carried 142 21 to the parts of the body where it is needed. Digestion takes place in the ahnientary canal, partly in the stomach, but more in the intestine. As the result, the useless portions are separated and rejected, while the parts which can serve for nutriment are changed into forms in which they can be absorbed, taken into the circulation, and utilized. DIGESTION. The alterations which the food undergoes in digestion are brought about by substances called ferments, wliich are secreted by the digest- ive organs. The saliva in the mouth has the power of changing insoluble starches into soluble sugar, but as the food stays in the mouth only a short time, there is generally little chance for such action. The saliva, however, helps to fit the food to be more easily worked on by the stomach. The gastric juice of the stomach acts upon protein, and the pancreatic juice of the intestine upon protein, fats, and carbo- hydrates. The action of all the ferments is aided by the fine division of the food by chewing and by the muscular contractions, the so-called peristaltic action, of the stomach and intestine. These latter motions help to mix the digestive juices and their ferments with the food. The parts of the food wliich the digestive juices can not dissolve, and which therefore escape digestion, are periodically given off by the intestine. Such solid excreta, or feces, include not only the particles of undigested food, but also the so-called metabolic products, i. e., residues of the digestive juices, bits of the lining of the alimentary canal, etc. ABSORPTION AND ASSIMILATION. The digested food finds its way through the walls of the alimentary canal, and at this time and later it undergoes remarkable chemical changes. 'When finally the blood, supplied with the nutrients of the digested food and freighted with oxygen from the lungs, is pumped from the heart all over the body it is ready to furnish the organs and ti.ssues with the materials and energy which they need for their pecul- iar functions; at the same time it carries away the waste which the exercise of these functions has produced. It is a characteristic of living body tissue that it can choose the necessary materials from the blood and build them into its own structure. IIow it does this is one of the mysteries of physiology. The body, as we have learned, has also the power of consuming not only the materials of the food, but also parts of its own structure for the production of muscular work, or heat, or to protect more important parts from consumption. IIow it does this is another mystery, still to be explained. 22 EXCRETION. After the material has been thus assimilated and utilized the result- ing waste products must be removed from the body. The chemical elements which this waste contains are of course the same as those making up the structure of the body and the food — carbon, oxygen, hydrogen, nitrogen, calcium, phosphorus, sulphur, etc. Most of the carbon and part of the oxygen are given off from the lungs as carbon dioxid. Hydrogen unites with more oxygen to form water, which is passed off in vapor from the lungs, in perspiration from the skin, and in urine from the kidneys. Almost all the nitrogen is excreted in the urine. Waste mineral matters are given off to some extent in the perspiration, but mainly through the kidneys and intestines. APPARENT AND ACTTJAIi DIGESTIBILITY. The real nutritive value of a food, then, depends not simply on the proportions of nutrients which it contains, but also on the amount of those nutrients which can be made available to the body by digestion for building material and for fuel. Part of the food eaten escapes digestion and is given off from the body in the feces. If we subtract the amount of this undigested residue from the total food, the remain- der will be the amoiuit actually digested in the stomach and intestines absorbed through their walls, and taken into the circulation. This difference between the amounts eaten and those undigested represents the actual digestibility of food. A part of the food taken into the circulation, however, is later returned again to the alimentary canal mainly in the digestive juices that are needed for digesting the food. The material thus removed from circulation and returned to the ali- mentary canal, which consists of so-called metabolic products, is excreted with the undigested residue in the feces. The remainder of the food taken into the circulation represents the amount retained by the body for building material and for fuel. The difference between the food which is absorbed and that which the body secures, therefore, is represented by the metabolic products. By the present methods of experimenting, however, the portion of the feces that consists of metabolic products can not be satisfactorily distinguished from the imdigested residue. It is very difficult, therefore, to determine the actual digestibility, but comparatively easy to estimate the apparent digestibility of food. " Suppose, for instance, that 15 per cent of the protein in a specimen of bread is excreted, then 85 per cent remains for the use of the body. alt would be more exact to use different terms to denote the apparent digestibility of food as distinguished from its actual digestibihty. It has therefore been proposed to limit the use of the term digestibihty to actual digestibihty and employ the term availabihty when apparent digestibihty, as ordinarily determined in nutrition investigations, is meant. (See Connecticut Storrs Station Eeport 1899, p. 69.) 23 If the bread has 8.4 per cent of protein, 100 pounds will have 8.4 pounds, of which 85 per cent or 7.1 pounds will be utilized by the body. Table III (p. 28) gives details regarding the proportions of digestible nutrients in different food materials. EASE AND QUICKNESS OF DIGESTION. The terms digestible, indigestible, etc., as here used refer simply to the food w-hich is or is not available for the general nourishment of the body after the process of digestion is completed. In common parlance, however, they are used more loosely as referring to the ease and qiiickness of digestion, and to the general healthfulness of food. One kind of food — bread, for instance — is spoken of as "simple" and "digestible," and another, like fruit cake, as "rich" and "indigest- ible." There is often much practical truth behind such statements, though little is definitely known concerning the time or labor required to digest different kinds of food. Among the earliest and most famous experiments concerning the time required for digestion in the stomach are those made by Dr. Wil- liam Beaumont, V. S. A., between 1825 and 1833. His subject was a French-Canadian trapper, a man quite normal except for an aperture through the abdomen into the stomach made by a gunshot wound, and closed only by a valve which had developed over it. By pressing the valve inward the contents of the stomach could be observed or removed at will, thus affording excellent opportunity to study the action of the gastric juice. Dr. Beaumont fed the man on various diets, and noted the different conditions accompanying each. The book in which he describes his experiments "contains a table of the average time required for the stomach to digest various articles of diet, from which many of the statements still current concerning the relative digestibility of different foods are taken. One of Dr. Beaumont's general deductions was that most of the common foods required from 2 to 4 hours. He says further : "The time required for the digestion of food is various, depending upon the quantity and quality of the food, state of the stomach, etc., but the time ordinarily re(|uired for the disposal of a moderate meal of the fibrous parts of meat, with bread, etc., is from 3 to 3^ hours." Valuable and interesting as Dr. Beaumont's book undoubtedly is, its conclusions can not be taken as final, because he does not state the amounts of food consumed. The science of nutrition in its develop- ment has also shown many errors in the reasoning. It should in jus- tice be said that Dr. Beaumont recognized the fact that his experi- ments had to do only with digestion in the stomach, or "chymifica- a Williairi B<;a)jmor)t, T\w Phymology of Digestion, with Experiments on the Gastric Juice. 2d ed. liuriington, Vt., 1847. 142 y 24 tion," as he terms it. Furthermore, his experiments have been often misquoted and given a different interpretation from that which he intended. Food does not ordinarily pass from the stomach into the intestine imtil it has been reduced to a Hquid or semiHquid condition. The length of time required for different foods to leave the stomach has been recently studied by Penzoldt with healthy men. He used a stomach tube for removing the stomach contents for examination. He found that the amount and consistency of food have a marked influ- ence on the rate of digestion in the stomach. Fluids leave the stomach more rapidly than other materials. From 6 to 7 ounces of water or other common beverages leave the stomach in IJ hours. Seven ounces of boiled milk leave the stomach in about 2 hours. Hot drinks do not leave the stomach more quickly than cold ones, nor does the quantity have much effect. Solid matter in solution or suspension delayed the passage of fluid from the stomach somewhat. The consistency of solid foods thus seems to have more effect upon digestibility than the amount consumed. The quantity eaten increases the length of time the material remains in the stomach, but not proportionally. To select a few examples of the time required for foods to leave the stomach: Two eggs (raw, poached, or in the form of an omelet), 7 ounces sweetbreads, 10 moderate-sized oysters, 7 ounces white-fish or 3| ounces of white bread, cauliflowers, or cherries, each left the stom- ach in from 2 to 3 hours. Eight and one-fourth ounces of chicken, 9 ounces of lean beef, 6 ounces boiled ham, 3 J ounces roast veal or beef- steak, 5J ounces of coarse bread, boiled rice, carrots, spinach, radish, or apple, left the stomach in 3 to 4 hours. Nine ounces of smoked tongue, 3i ounces smoked beef, 9 ounces roast goose, 5 J ounces string beans, or 7 ounces peas porridge, left the stomach in 4 to 5 hours. Generally speaking, the most readily digested animal foods were materials of soft consistency. White meats — for example, chicken — leave the stomach more quickly than red meats or dark meat — for instance, duck. The method of cooking also exerts a very marked influence on stomach digestion. Fresh fish was found to be more read- ily digested than meats. As regards vegetable foods in general, the consistency and the amounts of solid material were again the principal factors affecting the time required for digestion in the stomach. Mealy potatoes, for instance, were more easily digested than waxy potatoes, and mashed potato more readily than potato cut up in pieces. Fine bread was more quickly digested than coarse bread. There was not much differ- ence in the time required for bread crust, bread crumb, toast, new bread, and stale bread to digest in the stomach, provided all were equally well chewed. 25 It must be remembered that digestion continues in the intestine and that the total time required for the digestion and absorption of the nutrients in any given food material is not shown by such experiments. They find their chief application in prescribing a diet for invalids, as in such cases it is often desirable to require of the stomach only a limited amount of work. AGREEMENT OF FOOD WITH INDIVIDUALS. Digestibilit}" is often confused Avdth another very different thing, namely, the agreeing or disagreeing of food with the person who eats it. During the process of digestion and assimilation the food, as we have seen, undergoes many chemical changes, some of them in the intestines, some in the liver, muscles, and other organs. In these changes chemical compounds may b,e formed which are in one way or another unpleasant and injurious, especially if they are not broken down (as normally they are) before they have opportunity thus to act. Some of the compounds produced from the food in the body n\a,j be actually poisonous. Different persons are differently constituted with respect to the chemical changes which their food undergoes and the effect produced, so that it may be literally true that " one man's meat is another man's poison." Milk is for most people a very wholesome, digestible, and nutritious food, but there are persons who are made ill by drinking it, and they should avoid milk. The writer knows a boy who is made seriously ill by eating eggs. A small piece of sweet cake in which eggs have been used will cause him serious trouble. The sickness is nature's evidence that eggs are for him an unfit article of food. Some persons have to avoid strawberries. Indeed, cases in which the most wholesome kinds of food are hurtful to individual persons are, unfor- tunately, numerous. Every man must learn from his own experience what food agrees with him and what does not. How much harm is done by the injurious compounds sometimes formed from ordinary wholesome foods is seldom realized. Physio- logical chemistry is revealing the fact that these compounds may affect even the brain and nerves, and that some forms of insanity are caused by products formed by the abnormal transformations of food and body material. PROPORTIONS OF DIGESTIBLE NUTRIENTS IN FOOD MATERIALS. During the past few years many experiments have been made to test the proportions of nutrients digested from ordinary food mate- rials. In making the experiments the subjects are kept on a simple diet, all the food and solid excreta are analyzed, and the difference between the two is taken to represent the amount of food wliich the 26 body secures for nutriment. Most of the subjects have been people in good health; the great majority have been men, but a few women, and especially children. From comparison of the results of many such experiments much interesting knowledge has been gained of the relative digestibiUty of different kinds and classes of foods. In general it may be said that probably most foods used by man are more completely digested than is ordinarily supposed, so that the bulk of the intestinal excretion is made up of metabolic products. Some foods, however, contain large proportions of material upon which the digestive juices can not so act as to make them capable of being absorbed. Thus the outer hull of the wheat grain contains woody substance which passes through the alimentary canal of man undi- gested, though animals, like cows and sheep, can digest a large part of it. It has been found that in the total food of an ordinary mixed diet, on the average, about 92 per cent of the protein, 95 per cent of the fats, and 97 per cent of the carbohydrates are retained by the body. In the average proportions in which the different animal and vegetable foods are combined in the diet about 97 per cent of the protein, 95 per cent of the fats, and 98 per cent of the carbohydrates of the animal foods are digested, while only 84 per cent of the protein, 90 per cent of the fats, and 97 per cent of the carbohydrates of the vegetable foods are digested. Animal foods, therefore, seem to have a greater digestibility than vegetable, especially as regards the protein they contain. The digestibility of a given article of food depends, of course, upon the digestibility of the different classes of nutrients and upon the relative proportion in which these nutrients occur. Thus, of two cereals con- taining about the same amount of dry matter, but with different pro- portions of protein and carbohydrates, the one with the larger propor- tion of the less digestible protein and the smaller proportion of the more digestible carbohydrates will be, on the whole, less completely digested. The figures given in Table I (p. 16) do not, then, represent the nutrients actually available for the uses of the body, but those con- tained in the food before it is eaten. The nutrients actually available must be calculated from the total amounts shown in the table by use of the proper factors for digestibility. Thus if 53.1 per cent of bread is carbohydrates the percentage of carbohydrates which the body will obtain from a given amount of bread will be 98 per cent of 53.1, or 52 per cent of the weight of the bread. Similarly the fuel value given is not the heat of combustion of the food consumed, but that of the nutrients actually oxidized in the body. This fuel value may be calcu- lated from the proportions of digestible nutrients and the fuel values of each as learned by experiment. 142 27 The proportions of the several nutrients which the body retains for its use are commonly called percentages or coefficients of digestibility . <» From the results of a large amount of experimenting it appears that the coefficients of digestibility and the fuel value per pound of different food materials or groups of materials are approximately as follows: Tabi-e II. — Coefficients of digestibility and fuel value per pound of nutrients in different groups of food materials. Kind of food. Meats and fish Eggs • Dairy products Animal food (of mixed diet) Cereals Legumes (dried) Sugars Starches Vegetables Fruits Vegetable foods (of mixed diet) . Total food (of mixed diet) Protein. Digesti- blUty. Per cent. 97 97 97 97 85 78 Fuel value per pound. Calories. 1,940 1,980 1,940 • 1,940 1,750 1,570 1,410 1,520 1.840 1,820 Fat. Digesti- bility. Per cent. 95 95 95 95 90 90 Fuel value per pound. Calories. 4,040 4,090 3,990 4,050 3,800 3,800 3,800 3,800 3,800 4,050 Carbohydrates. Digesti- bility. Per cent. 98 98 98 98 98 97 98 98 95 90 97 97 Fuel value per pound. Calories. 1,730 1,730 1,730 1,730 1,860 1,840 1,750 1,860 1,800 1,630 1,820 1,820 The figures of Table III (p. 28) show the digestible nutrients and available energy in a number of common food materials, as computed from the figures in Table I, by use of the factors given in Table II. The further assumption is made that 75 per cent of the ash is digesti- ble. The figures in the third column of Table III show the total quantity of indigestible nutrients. The term used as the heading of the last column, ''nutritive ratio," or, as it is sometimes and perhaps more accurately called, "nutrient ratio," requires a word of explana- tion. The term nutritive ratio is used to express the ratio of digesti- ble protein to digestible fuel ingredients (fats and carbohydrates) in any food material or diet. In calculating this ratio 1 pound of fat is taken as equivalent to 2\ pounds of carbohydrates — this being approximately the ratio of their fuel values — so that the nutritive ratio is actually that of the protein to the carbohydrates plus 2 J times the fat. "It should be understood that the terms "digestibility" and "digestible nutrients "and "wjefRcients of digestibility," a.s u.sed in the following tables and the accompanying expla- nations, refer to apparent digestibility (see p. 22). 142 28 Table III. — Nutrients and energy of digestible portion of some common foods, nutritive ratios. with Kind of food materials. ANIMAL FOOD. Beef, fresh: Chuck, ribs -Lom, medium Ribs '. Round, medium Shoulder and clod Beef, dried and smoked Veal: Cutlets, round Leg Mutton: Leg Loin Pork, fresh: Loin, chops Ham Pork, salted and smoked: Bacon Ham Salt, fat Poultry: Fowl Turkey Fish, fresh: Cod, dressed Mackerel Shellfish: Oysters, solids Fish, preserved and canned: Cod, salt Salmon, canned Eggs, uncooked Dairy products: Whole milk Skim milk Cream Butter VEGETABLE FOOD. Cereals, etc.: Corn meal Oat breakfast food Rye flour Rice Wheat flour, patent process Wheat breakfast food. . Bread, etc.: Bread, white wheat Crackers, cream Vegetables: Beans, white, dried . . . . Beets, fresh Cabbage Potatoes Squash Sweet potatoes, fresh... Tomatoes Fruits: Apples Bananas Grapes Oranges Strawberries Per cent. 16.3 13.3 20.8 7.2 16.4 4.7 3.4 14.2 18.4 16 19.7 10.7 7.7 13.6 25.9 22.7 29.9 44.7 24.9 'ii.'2' Per cent. 52.6 52.5 43.8 60.7 56.8 53.7 68.3 60.1 51.2 42 41.8 17.4 34.8 7.9 47.1 42.4 58.5 40.4 88.3 40.2 63.5 65.5 87 90.5 74 11 12.5 7.8 12.9 12.3 12 9.6 35.3 6.8 12.6 70 77.7 62.6 44.2 55.2 94.3 63.3 48.9 58 63.4 85.9 Per cent. 1.4 1.6 1.8 1.4 1.2 4.5 1.2 1.1 1.8 1.9 4.4 3.1 6.4 1.2 1.6 .6 5.1 1.9 1.1 .5 .3 1.1 4.9 3.3 5.1 2.9 2.9 3.4 3.8 2.9 4.5 .6 1.2 .4 1.6 .5 1.2 1.6 1.7 1 1 Digestible nutrients. Per cent. 15 15.6 13.5 18.4 15.9 25.6 19.5 15 14.6 13.1 13 13.1 13.8 1.8 13.3 15.6 10.8 9.9 15.5 21.1 12.7 3.2 3.3 2.4 1 7.8 14.2 5.8 6.8 9.7 10.3 7.8 8.2 17.5 1.1 1.2 1.5 .6 1.2 .7 Per cent. 14.3 16.6 20 12.2 9.3 6.6 7.1 7.5 14 26.9 23 24.6 59.1 31.7 81. 9 11.7 17.5 4 1.2 .4 11.5 3.8 .3 17.6 1.7 6.6 .9 1.6 1.2 10.9 1.6 .1 .2 .1 .2 .5 .4 .3 .4 1.1 .1 .5 Per cent. 5 5.1 4.5 73.9 64.9 77.1 77.4 73.6 73.7 68.3 57.8 7.3 4.6 14 4.3 20.8 3.7 9.7 12.9 13 7.7 6.3 Per cent. 0.6 .7 .5 .8 .7 5.5 Calo- ries. 910 1,025 1,135 890 715 790 .8 .7 695 625 .6 .5 1,415 .6 .6 1,245 1,320 3.1 3.2 2.9 2,720 1,635 3,555 . a .6 766 1,060 .6 .5 220 370 .8 225 13.9 2 ".7 325 915 635 .5 .5 .4 2.3 310 165 865 3,410 .8 1.4 .5 .3 1,640 1,800 1,620 1,625 .4 1 1,635 1,680 .8 1.3 1,200 1,925 2.6 .7 .7 .6 .3 .7 .4 1,620 160 115 295 100 440 95 .2 .6 .3 .3 .5 190 260 295 150 150 142 29 The principal data included in Table III are shown in graphic form in Chart 1. Chart 1.— COMPOSITION OF FOOD IvIATERIALS Nutritive ingredients, refuse, andfu£l value. DtcftJtihle miiyitTtts InoUqtttthU luUntnts fiorv nutntnh Refujt Carbo- MinercU- bydU-citej niccUtrt Muscle making. Fuel ingredients. 30 It is to be observed that the values given in Table III, like those of Table I, represent averages. Different specimens of the same kind of food material differ in composition, digestibility, and nutritive value. Materials which are grouped in the same class may also differ more or less in this respect. Thus potatoes, turnips, cabbage, or even different specimens of the same vegetable, may differ in the proportions of nutrients digested. The figures in Table III, therefore, are to be taken as only approximate values. PREPARATION OF FOOD— COOKING. The cooking of food has much to do with its nutritive value. Many - articles which, owing to their mechanical condition or other cause, are quite unfit for nourishment when raw are very nutritious when cooked. It is also a matter of common experience that a well-cooked food is wholesome and appetizing, while the same material badly cooked is unpalatable. There are three chief purposes of cooking. The first is to change the mechanical condition so that the digestive juices can act upon the food more freely. Heating often changes the structure of food materials very materially, so that they are more easily chewed and more easily and thoroughly digested. The second is to make it more appetizing by improving the appearance or flavor, or both. Food which is attractive to the taste quickens the flow of saliva and other digestive juices, and thus digestion is aided. The third is to kill by heat any disease germs, parasites, or other dangerous organ- isms it may contain. This is often a very important matter, and applies to both animal and vegetable foods. The cooking of meats develops the pleasing taste and odor of extractives and that due to the browned fat and tissues and softens and loosens the protein (gelatinoids) of the connective tissues, and thus makes the meat more tender. Extreme heat, however, tends to coagulate and harden the albuminoids of the lean portions, and also weakens the flavor of extractives. If the heating is carried too far a burned or charred product of bad flavor results. Meats lose weight in cooking. A small part of this is due to escape of meat juices and fat, but the chief part of the material lost is simply water. The nutritive value of a meat soup depends upon the sub- stances which are dissolved out of the meat, bones, and gristle by the water. In ordinary meat broth these consist almost wholly of extract- ives and salts, which are very agreeable and often most useful as stimu- lants, but have little or no value as actual nutriment, since they neither build tissue nor yield energy. The principles which underUe the cook- ing of fish are essentially the same as with meats. In many vegetables the valuable carbohydrates, chiefly microscopic starch grains, are contained in tiny cells with thick walls on which the 31 digestive juices have little effect. The heat of cooking, especially with the aid of water, ruptures these walls and also makes the starch more soluble. The heat also caramelizes a portion of the carbohy- drates and produces agreeable flavors in this and other ways. In breads, cakes, pastry, and other foods prepared from flour, the aim is to make a palatable and lighter porous substance more easily broken up in the alimentary canal than the raw materials could be. Sometimes this is accomplished simply by means of water and heat. The heat changes part of the water in the dough into steam, which, in trying to escape, forces the particles of dough apart. The protein (gluten) of the flour stiffens about the tiny bubbles thus formed and the mass remains porous even after the steam has escaped. More often, however, other things are used to "raise" the dough — such as yeast and baking powder. The baking powder gives off the gas carbon dioxid and the yeast causes fermentation in the dough by which carbon dioxid is produced. This acts as the steam does, only much more powerfully. When beaten eggs are used, the albumen incloses air in bubbles which expand, and the walls stiffen with the heat and thus render the food porous. Scrupulous neatness should always be observed in keeping, hand- ling, and serving food. If ever cleanliness is desirable, it must be in the things we eat, and every care should be taken to insure it for the sake of health as well as of decency. Cleanliness in this connection means not only absence of visible dirt, but freedom from undesirable bacteria and other minute organisms, and from worms and other para- sites. If food, raw or cooked, is kept in dirty places, peddled from dirty carts, prepared in dirty rooms and in dirty dishes, or exposed to foul air, disease germs and other offensive and dangerous substances can easily get in. Food and drink may, in fact, be very dangerous purveyors of dis- ease. The bacteria of typhoid fever sometimes find their way into drinking water, and those of typhoid and scarlet fevers and diphtheria into milk, and bring sickness and death to large numbers of people. Oysters which are taken from the salt water where they grow and "floated" for a short time in brackish water near the mouth of a stream, have been known to be infected by typhoid fever germs brought into the stream by the sewage from houses where the dejec- tions from patients had been thrown into the drains. Celery or let- tuce grown in soil containing typhoid germs has been thought to con- vey this disease. Food materials may also contain parasites, like tapeworms in beef, pork, and mutton, and trichinae in pork, which are often injurious and sometimes deadly in their effect. This danger is not confined to animal foods. Vegetables and fruits may become contaminated with 142 32 eggs of numerous parasites from the fertilizers applied to them. Kaw fruits and vegetables should always be Terr thoroughly washed before seiwing if there is any doubt as to their cleanliness. If the food is sufficiently heated in cooking, all organisms are killed. Sometimes food midergoes decomposition in which injurious chem- ical compounds, so-called ptomaines, are formed. Poisoning by cheese, ice cream, preserved hsh, canned meats, and the like has been caused in this way. The ptomaines often withstand the heat of cooking. In some ceases it ha^ been foimd that foods are adulterated ^^ith compotmds injimous to health: btit sophistication in which harmless articles of inferior cost or quahty are added is more common. Dainty ways of serving food have a tisefulness beyond their esthetic value. Everyone knows that a feeble appetite is often tempted by a tastefully garnished dish, when the same material carelessly served would seem quite tmpalatable. Fi.u"thermore, many cheap articles and •'• left-overs "' when well seasoned and attractively served may be just as appetizing as dearer ones, and will usually be foimd quite as nutritiotis. DIETAEIES AlfD DIETAEY STANDAEDS. The information gained from a study of the composition and nutri- tive value of foods may be turned to practical accoimt by using it in planning diets for different individuals or classes of individuals or in estimating the true nutririve value of the food acttially constmied by families or individuals. By comparing the results of many such inves- tigations with the results of acctu"ate physiological experimenting it is possible to learn about how much of each of the nutrients of common foods is needed by persons of different occupations and habits of hfe, and from this to compute standards representing the average require- ments for food of such persons. 3so:thods of making dietary studies. During the last twenty years much of this practical appHcation of the chemistjy of food has been made in the study of actual dietaries. Much work of this kind has been done in England, Germany, Italy, Etissia. Sweden, and elsewhere in Etirope, and in Japan and other oriental countries. "VTithin the past dozen years extensive sttidies have been made iu the United States. The simplest way of making stich inquiries is to find otit what kinds and quantities of food are used dming a given period in the household in which the study is made; to estimate the amounts of variotis nutrients which the different mate- rials contain by means of figures given for the average composition of the various articles in tables, like Table I (p. 16), and then to calcu- 142 33 late the cost and amount of nutrients for each person. There are, however, several chances for error in such a method. In the first place, since different specimens of the same kind of food vary greatly in composition, it is often inaccurate to estimate the nutrients of one specimen from figures representing the average composition. Accord- ingly, in the more careful dietary studies, the composition of the food is determined by analyzing samples of materials actually used. Again, this method assumes that all the food is really consumed, whereas it is very plain that frequently no small portion is wasted in the kitchen or at the table. This difficulty is usually met by measuring and com- puting the amounts of nutrients in the waste and sometimes by analyz- ing samples of it. In preparing the results of dietary studies so that different studies may be compared, another difficulty appears. For example, in a fam- ily consisting of father, mother, and two children of different ages the amount of food taken by each is by no means the same, and it would be quite incorrect to divide the whole amounts consumed by four and rail the result the amount used per person. Men, as a rule, cat more than women, women more than young children, and persons of active habits more than those who take little muscular exercise. A coal heaver, who is constantly using up nutritive material of muscular tissue to supply the energy refjuired for his severe muscular work, needs a diet with more protein and higher fuel value than a book- keeper who sits at a desk all day. It is ordinarily estimated that, as compared with a man at moderate or light work, a woman under simi- lar conditions needs 0.8 as much food, and children amounts varying with their ages, and such figures are used to reduce the statistics of a dietary to the standard of one man at moderate work. The various factors commonly used in the United States in computing the results of dietary studies are as follows: Factors wied in calculating meals consumed in dietary studte/i. Man at hard muscular work requires 1.2 the food of a man at moderately active muscular work. Man with light muscular work and hoy l.S-16 years old require 0.0 I lie food of a man at moderately active muscular work. Man at sedentary occupation, woman at moderately active work, hoy IS-H, and girl ir>-10 years old require 0.8 the food of a man at moderately active mus*;ular work. Woman at light work, iKiy 12, and girl 13-14 years old require 0.7 the food of a man at mo0 aFata and carbohydrates in BUfficient amounta to furnish, together with tho protein, the indicated amount of energy. 142 36 The dietary standards « given in the table (pp. 34, 35) are based, as far as possible, upon the results of observation and experiment, but are at best general estimates and not guides to be blindly followed. They are subject to revision in the light of further experimental evidence. It will be observed that the amounts of energy provided in the American standards are somewhat larger than in the European standards (Voit's) . This corresponds to the observed fact that people in this country, more especially the working people, are as a rule better fed and do more work than those of corresponding classes in Europe. The quantities of pro- tein in these standards are larger in proportion to the fuel ingredi- ents— that is, the nutritive ratio is narrower — than is found in the average American diet. In this respect the standards agree more nearly with the diet of well-to-do people in Europe. It is believed that the larger amount of protein represents rather more nearly a physiological ration than do the proportions as found in the majority of actual dietaries. The results of a large amount of experimental investigation bear out the common belief that the American, as a rule, uses more food than the European of the same class. The character of the food is, however, quite different. The poor peasants of Russia and northern Germany live chiefly upon rye bread, potatoes, and some sort of fat. In Italy maize, chestnuts, and acorn meal form an important item in the diet of a considerable portion of the poorer population. The use of meat among the working population of most European and Asiatic countries is very much less general than in America, because its cost is prohibitive. In the majority of European dietaries the fats occur in relatively smaller and carbohydrates in relatively larger amounts than in Ameri- can dietaries. This is probably due in large measure to the smaller quantities of meats used in the former dietaries. Among the more scantily nourished peoples of the globe are the poor of India and China. They live largely on rice and other cereals and vegetables, with more or less of pulse and other legumes, and often on quantities which to the ordinary American would seem little more than a starvation diet. A close examination of the detailed statistics from which those of Table III (p. 28) have been selected shows that, although there may be occasional wide variations between two individuals of a given class in respect to the total amounts of food eaten, yet, on the whole, through extended periods, there are not unusually large variations in amounts of protein or energy in the food consumed by different individuals of the same class; that is, under similar conditions as regards work or rest. "For several years an effort has been made to collect statistical and experimental data with a view to revising dietary standards. The amount of data at present (1906) available is very large, and the work of systematizing it is well under way. It seems probable that the revised dietary standards will differ somewhat from the standards pubUshed in this and earUer publications of this Department. 142 37 MAKING HOME STUDIES OF DIETARIES. Any housekeeper who wishes to know how the nutritive value of the food she provides for her family corresponds with the dietary stand- ards can easily make a simple dietary study in her homo, and ])y so doing can perhaps not onh' provide meals that are more in accordance with the needs of her family, but frequently also save money by sub- stituting less expensive but equally nutritious and attractive food materials for some of those usually served. The simplest way to make such a study is to weigh all different kinds of food materials in the house at a given time, sa}^ after supper, recording the weights in a convenient book. All the food purchased during the days during wliich the diet is being studied is weighed and recorded, and at the close of the study, which may be conveniently of seven or ten daj^s' duration, all food- materials remaining on hand are weighed as before. From the quantities of the different kinds of food on hand at the beginning and purchased during the period are sub- tracted the quantities left on hand at the close of the study. The dif- ference represents the amounts used. The quantity of nutrients in the different materials is calculated from the figures for percentage composition given in Table I, or in other more comprehensive tables®. In order to express the quantities of nutrients in values per man per day, the number of meals taken by different members of the family are multiplied by the factors given on page 33, pointing off one deci- mal place. The result gives the equivalent number of meals for a man. The equivalent number of meals taken divided by 3 gives the equivalent number of days for one man. The total nutrients for the whole period, divided by this latter quantity, gives the nutrients per man per day. From these latter figures the fuel value of the diet can be computed by means of the factors given on page 33. In a similar way the value of any menu for one day or one meal may be calculated. It is to be remembered that in a short period, such as a day or two days, the diet may fluctuate according to the materials used so as to give more of one kind of nutrients and less of another, or more or less total nutrients than the average diet, while in periods of a week or ten days the diet is more likely to approach an average. ADAPTING FOOD TO THE NEEDS OF THE BODY. All persons are alike in that they must have protein for the building and repair of the bodily machine and fuel ingredients for warmth and work, but individuals differ in the amounts and proportions they require, and even among those in good health there are many who are obliged to avoid certain kinds of food, while invalids and people with weak digestion must often have special di(!t. •See especially U. S. Dcpt. Apr., (Wkc. of Experiment Stations Bill. 2K, rciviwd. M8 38 For people in good health and with good digestion there are two important rules to be observed in the regulation of the diet. The first is to choose the things which "agree" with them, and to avoid those which they can not digest and assimilate without harm. The second is to use such kinds and amounts of food as will supply all the nutrients the body needs and at the same time avoid burdening it with superflu- ous material to be disposed of at the cost of health and strength. For guidance in this selection, nature provides us with instinct, taste, and experience. Physiological chemistry adds to these the knowledge — still new and far from adequate — of the composition of food and the laws of nutrition. In our actual practice of eating we are apt to be influenced too much by taste — that is, by the dictates of the palate; we are prone to let natural instinct be overruled by acquired appetite, and we neglect the teachings of experience. We need to observe our diet and its effects more carefully and to regulate appetite by reason. In doing this we may be greatly aided by the knowledge of what our food contains and how it serves its purpose in nutrition. Though there may be differences among abnormal persons, for the great majority of people in good health the ordinary food materials — meats,fish,eggs,milk,butter,cheese, sugar, flour, meal,and potatoes and other vegetables — make a fitting diet, and the main question is to use them in the kinds and proportions fitted to the actual needs of the body. When more food is eaten than is needed, or when articles difficult of digestion are taken, the digestive organs are overtaxed, if not posi- tively injured, and much energy is thus wasted which might have been turned to better account. The evils of overeating may not be felt at once, but sooner or later they are sure to appear — perhaps in an exces- sive amount of fatty tissue, perhaps in general debility, perhaps in actual disease. The injurious effects of food which does not "agree" with a person have already been pointed out. ADVANTAGES OF SEVERAL MEALS A DAY. The theory is advanced from time to time that one or two meals a day are preferable to the three commonly served in this country. If the same amount of food is to be eaten it is hard to see the advantage of two very hearty meals over three ordinary ones. The best physi- ological evidence implies that moderate quantities of food taken at moderate intervals are more easily and completely digested by ordi- nary people than larger quantities taken at long intervals. If the food ordinarily taken is considered excessive and the aim is simply to reduce the amount, it would seem more rational to make all the meals lighter than to leave out one. The very fact that the custom of eating a number of meals a day has so long been almost universal indicates that it must have some advantages which instinct, based upon experi- ence, approves and justifies. 39 •^ PECTJNIAKY ECONOMY OF FOOD. Although the cost of food is the principal item in the living expenses of a large majority of the people, and although the physical welfare of all is so intimately connected with and dependent upon diet, very few of even the most intelligent have any clear ideas regarding the actual nutriment in the different food materials they use. In too many cases even those who wish and try to economize know very little as to the combinations which are best fitted for their nourishment and have still less information as to the relation between the real nutritive value of different foods and their cost. The question here to be considered is this: Of the different food materials which are palatable, nutritious, and otherwise suited for nourishment, what ones are pecuniarily the most economical ; in other words, what ones furnish the largest amounts of available nutrients at the lowest cost ? In answering this question it is necessary to take into account not only the prices per pound, quart, or bushel of the dif- ferent materials, but also the kinds and amounts of the actual nutri- ents they contain and their fitness to meet the demands of the body for nourishment. The cheapest food is that which supplies the most nutri- ment for the least money. The most economical food is that which is cheapest and at the same time best adapted to the needs of the user. There are various ways of comparing food materials with respect to the relative cheapness or deamess of their nutritive ingredients. For instance, from the proportions of available nutrients and energy in different food materials given in Table III we may calculate the cost of the different nutrients per pound and of energy per 1,000 calories in any given material for which the price per pound is known. Thus, for the different food materials given in Table V (p. 40), when the price of any material is that given in the first column, the cost of pro- tein and energy will l^e as given in the second and third columns. These figures show the relative economy of the various foods as sources of protein and sources of energy. Of course the amount of energy that would be obtained in a quantity of any given material sufficient to furnish a pound of protein would vary with the amounts of fats and carbohydrates accompanying the protein; and on the other hand, the quantities of the different materials that would furnish 1,000 calories of energ}' would contain different amounts of protein. The figures for cost of protein leave the carbohydrates and fats out of account, and tho.se for energy take no account of the protein. Hence the figures for either protein or energy alone give a very one-sided view of the rela- tion between nutritive value and money cost. A better way of estimating the relative pecuniary economy of differ- ent food materials is found in a comparison of the (|uantities of both nutrients and energy wliich can be obtained for a given sum, say 10 143 40 cents, at current prices. This also is illustrated in Table V, which follows : Table V. — Comparative cost of digestible nutrients and energy in different food materials at average prices. [It is estimated that a man at light to moderate muscular work requires about 0.23 pound of protein and 3,050 calories of energy per day.] Kind of food material. Beef, sirloin Do Do Beef, round Do Do Beef, shoulder clod Do Beef, stew meat Beef, dried, chipped Mutton chops, loin Mutton, leg Do Roast pork, loin Pork, smoked ham Do Pork, fat salt Codfish, dressed, fresh Halibut, fresh Cod, salt Mackerel, salt, dressed Salmon, canned Oysters, solids, 50 cents per quart Oysters, solids, 35 cents per quart Lobster, canned Butter Do Do Eggs, 36 cents per dozen Eggs, 24 cents per dozen Eggs, 12 cents per dozen Cheese Milk, 7 cents per quart Milk, 6 cents per quart Wheat flour Do Corn meal, granular Wheat breakfast food Oat breakfast food Oatmeal Rice Wheat bread Do Do Rye bread Beans, white, dried Cabbage Celery Corn, canned Potatoes, 90 cents per bushel . . Potatoes, 60 cents per bushel . . Potatoes, 45 cents per bushel . . Turnips Apples Bananas Oranges Strawberries Sugar Price per pound. Cents. 25 20 15 16 14 12 12 9 5 25 16 20 16 12 22 18 12 10 18 7 10 12 Cost of 1 pound pro- tein, a Dollars. 1.60 1.28 .96 .87 .76 .65 .75 .57 .35 .98 1.22 1^37 1.10 .92 1.60 1.30 6.67 .93 1.22 .45 .74 .57 4.30 3.10 1.02 20.00 25.00 30.00 2.09 1.39 .70 .64 1.09 .94 .31 .26 .32 .73 .53 .29 1.18 .77 .64 .51 .65 .29 2.08 6.65 4.21 1.00 .67 .50 1.33 5.00 10.00 12.00 8.75 Cost of 1,000 calories energy (a) Cents. 25 20 15 18 16 13 17 13 7 32 11 22 18 10 13 11 3 46 38 22 9 13 111 Amounts for 10 cents. Total weight of food mate- rial. Pounds 0.40 .50 .67 .63 .71 .83 .83 1.11 2 .40 .63 .50 .63 .83 .45 .56 .83 1 .56 1.43 1 .83 .40 .56 .56 .50 .40 .33 .42 .63 1.25 .63 2.85 3.33 3.33 4 4 1.33 1.33 2.50 1.25 1.67 2 2.50 2 2 4 2 1 6.67 10 13.33 10 6.67 .1.43 1.67 1.43 1.67 Pro- tein. Pound. 0.06 .08 .10 .11 .13 .15 .13 .18 .29 .10 .08 .07 .09 .11 .06 .08 .02 .11 .08 .22 .13 .18 Fat. Pound. 0.06 .08 .11 .08 .09 .10 .08 .10 .23 .03 .17 .07 .09 .19 .14 .18 .02 .01 .20 .10 .02 .03 .01 .10 .01 .01 .40 .32 .27 .04 .06 .11 .20 .11 .13 .03 .04 .07 .02 .09 .16 .02 .02 .03 .01 .03 .01 .01 .01 .01 .01 .01 .02 .01 Carbohy- drates. Pounds. .01 .02 .02 .14 .17 2.45 2.94 2.96 1.66 .97 .87 1.04 1.30 1.04 1.16 .18 .05 .18 .93 1.40 1.87 .54 .65 .18 .13 .09 1.67 a The cost of 1 pound of protein means the cost of enough of the given material to furnish 1 pound of protein, without regard to the amounts of the other nutrients present. Likewise the cost of energy means the cost of enough material to furnish 1,000 calories, without reference to the kinds and propor- tions of nutrients in which the energy is supplied. These estimates of the cost of protein and energy are thus mcorrect in that neither gives credit for the value of the other. 142 41 The fourth cokmin in Table Y shows the total weight of each food material and the last four columns the amounts of different nutrients and of energy that can be obtained for 10 cents when the })rice per poimd is that given in the fiist column. Chart 2 illustrates graphically the facts brought out in this part of the table. Chabt 2.— pecuniary ECONOMY' OF FOOD. Anwunts of actually nutritive ingredients obtained in differefitfood materials for 10 cents. [Amounts of nutrients in pounds; fuel value in calories.] J^tein. Rvts Carhoki/dratu Fuel Value. 42 Of course, the market prices of the different food materials would vary in different localities and at different times, but the prices here used are averages of such as are actually found in different parts of the United States in different years and seasons, and serve for coni- parison. It should be borne in mind that the figures here given represent only the cost of the materials as purchased in the market. In com- paring the relative economy of the different food materials no account is taken of the cost of cooking or of the convenience of preparation for the table, which are sometimes even more important from the stand- point of actual economy than the market prices. The figures of Table V show, for instance, that 10 cents spent for beef sirloin at 20 cents a pound buys 0.5 pound of meat, which con- tains 0.08 pound of protein, 0.08 pound of fat, and 515 calories of energy, actually available to the body, while the same amount spent for oysters at 35 cents a quart would buy a little over half a pound of oysters, con- taining 0.03 pound of protein, 0.01 pound of fat, 0.02 pound of carbo- hydrates, and 125 calories of energy; or if spent for cabbage, at 2| cents a pound, it would buy 4 pounds, containing 0.05 pound of pro- tein, 0.01 pound of fat, 0.18 pound of carbohydrates, and 460 calories of energy, while of wheat flour at 3 cents a pound it would buy 3 J pounds, containing 0.32 pound of protein, 0.03 pound of fat, 2.45 pounds of carbohydrates, and 5,410 calories of energy. Comparing the various materials in this way, it becomes clear that the fresh vege- tables are the dearest sources of protein, meats and fish somewhat cheaper, and the cereals cheapest of all ; and that oysters and lobsters are the costliest sources of energy, followed by some of the green vege- tables and fruits, then the majority of the meats, next potatoes, and cheapest of all, the cereals. It is quite evident that the market price of food materials is not regulated by their actual value for nutriment. For instance, an ounce of protein or fat from the tenderloin of beef is no more nutritious than that from a round or shoulder, but it costs considerably more. The agreeableness of food to the palate or to the buyer's fancy has much to do in deciding current demand and consequent selling price. It may be said, however, that animal foods have some advantage over vege- table foods. Animal foods, such as meats, fish, milk, and the like, gratify the palate as many vegetable foods do not. Furthermore, what is of still greater weight in regulating the food habits of communi- ties by whose demand the prices are determined, they satisfy an actual need by supplying protein and fats in which the vegetable foods, except cereal grains and leguminous seeds, are largely lacking. Moreover, as has previously been explained, the animal foods are in general more easily and completely digested than are the vegetable, especially as regards protein. Thus there is doubtless good ground for paying 142 43 somewhat more for the same total quantity of nutritive material in the animal food. One point to be especially noted here is the difference in the cost of nutrients in foods already prepared for use and in the same materials not so prepared. For instance, wheat made into ordinary prepared breakfast cereal might contain no more available protein or energy than the same wheat made into white or graham flour, but the break- fast cereals cost more than the flour per pound. At the same time, the breakfast foods afford a pleasing variety in the diet, and often require little or no cooking and are therefore very convenient; while the fioiu- must be made into bread or other food at more expense of labor, fuel, etc. If the breakfast cereal does not cost much more than the flour the difference may be offset by the convenience of prepara- tion for the table, the palatabihty, and the pleasing variety it gives. Many of the breakfast foods are advertised as having an especially high nutritive value. If the statements often made m advertising these could be beUeved they would have some nutritive property not found in flours and meals groimd from the same grains. For these claims there is no ground. The breakfast foods made from wheat, com, oats, and other cereals contain no nutritive material other than that which is in the original grain, and which is also found in the ordi- nary flours and meals made from the same grains; and when the two kinds of food are equally well cooked there is no experimental evidence to show any difference in the thoroughness of digestibility. The retail prices of the breakfast foods are from two to five times as large as those of the ordinary products, like flour and meal. The advertise- ments, which often claim nutritive values that are fictitious, do not give any suggestion of the high price of the nutrients in the prepared foods as compared with that of the same amounts in the ordinary products, nor do purchasers generally reaUze how expensive these pre- pared foods are. ERRORS IN FOOD ECONOMY. Scientific research, interpreting the observationa of practical life, indicates that a fourfold mistake in food economy is very commonly made. First, the costlier kinds of food are used when the less expen- sive are just as nutritious and can bo made nearly or quite as palatal)lo. Secondly, the diet is apt to be one-sided, in that foods are used which furnish relatively too much of the fuel ingredients and too little of the. flesh-forming materials. Thirdly, excessive quantities of food are used; part of the excess is eat<;n and often to the detriment of health; part is thrown away in the table and kitchen wastes. Finally, serious errors in cooking are committed. For the well-to-do the worst injury is that to health; but people of small incomes suffer the additional disadvantage of the injury to purse. 44 Indeed, to one who looks into the matter it is surprising to see how much people of limited incomes lose in these ways. It is the poor man's money that is most injudiciously spent in the market and the poor man's food that is most badly cooked at home. NEEDIZESS USE OF EXPENSIVE FOODS. A common mistake in pui'chasing food is in buying the more expen- sive kinds when cheaper ones would serve the purpose just as well. This is often done under the impression that there is some pecuhar virtue in the costlier materials and that economy in the diet is detri- mental to dignity and welfare. Unfortunately it is too often the case that those who are most extravagant in this respect are the ones who can least afford it. On the other hand, there is frequently a desire to economize, but a lack of knowledge of the best method of doing so. Many a housekeeper who sincerely tries to do the best for those to be provided for, but whose every cent must tell, buys eggs at 25 cents a dozen, or sirloin steak at 20 cents a pound, when, for the same amoimt of money, it would be possible to get twice as much nourishment from a cheaper cut of meat, which, with a little skill in preparation and cooking, could be made into a tasty dish such as persons in far easier circumstances would not hesitate to set upon their tables. The difficulty is the ignorance of the simple principles of nutrition. That ignorance results in a great waste of money. The maxim "that the best is the cheapest," as popularly understood to apply to the higher-priced materials, is not true of food. The larger part of the price of the costlier foods is paid for appearance, flavor, or rarity. While the dearer articles are often more pleasing to the palate, and are sometimes more easily cooked or possess a finer flavor, they are no more digestible nor nutritious than the cheaper ones. People who can afford them may be justified in buying them, but for persons in good health and with limited means they are not economical, and often increase the cost of food out of all proportion to nutrients furnished. In the course of some dietary studies made in one of the poorer dis- tricts of Chicago it was found that a woman, whose husband was out of work and whose family was living on a few cents a day, bought lettuce, an article so innutritions that, at least when out of season and high in price, it is a luxury even for the rich, while she had to do without nutritious food. No one can object to the use of lettuce, or any other wholesome food, when the purse allows, but it is pitifully bad economy in such cases to buy foods which simply please the palate while the body goes without proper nourishment. The plain, substantial, standard food materials, like the cheaper cuts of meat and fish, milk, flour, com meal, oatmeal, beans, and pota- toes, are as digestible and nutritious and as well fitted for the nourish- ment of people in good health as are any of the costlier materials. We endeavor to make our diet suit our palate by paying high prices in the market rather than by skillful cooking and tasteful serving 45 at home. The remedy for this evil will be found in an understanding of the elementary facts regarding food and nutrition, in a better knowledge of cooking and serving food, and in the acceptance of the doctrine that economy is not only respectable but honorable. The soup kitchens which have been established in many cities, where meals planned according to accepted dietary standards are sold at very low and yet profitable rates, should furnish their patrons with object lessons on the food-purchasing power of money. DANGER OF A ONE-SIDED DIET. Unless care is exercised in selecting food a diet may result wliich is one-sided or badly balanced — that is, one in wliich either protein or fuel ingredients are provided in excess. If a person consumes large amounts of meat and little vegetable food, the diet will be too rich in protein and may be harmful. On the other hand, if pastry, butter, and such foods are eaten in preference to a more varied diet, the food will furnish too much energy and too little building material. Extreme illustrations of such a one-sided diet are found in the food of those persons who live largely on bread and tea, or others who live on com meal, fat pork, and molasses. The "hog and hominy" diet supplies liberal quantities of energy, but is very deficient in protein, as illustrated by the diet of negroes in the "black belt," with 62 grams of protein and 3,270 calories of energy per man per day. In this connection it should be said that most of our dietary stand- ards have been deduced from food investigations conducted with per- sons living in temperate climates. It is not improbable that those living in arctic regions and in the Tropics require nutrients in different proportions. It is a matter of common observation that in arctic regions much larger amounts of energy-yielding material, principally fat, are consumed than in warmer climates. Less definite informa- tion is available regarding food requirements in the Tropics; but it seems probable that when proper dietary conditions are followed some- what less food is consumed than in temperate regions, and that the nutrients are in somewhat difi"erent proportion. It is certain that a diet which would be entirely satisfactory in frigid regions would be one-sided in the Tropics, and vice versa. This subject is one which needs further investigation before definite conclusions can be drawn regarding the foods best fitted for extremes of heat or cold. "WASTE OF FOOD. The use of excessive quantities of food, which is a common dietary error in this country, among not only the well to do but also those in moderate circumstances, entails a waste of food in at least three ways: First. More food is eaten than can be properly utilized by the l)ody. Tliis is not universally true, for there are some people who do not cat enough for healthful nourishment. But the eating liabits of largo numbers are vicious, resulting not only in a loss of food material but ID an increase in the labor of digestion, to say nothing of the injurious 142 46 effects which overeating may have upon the bodily organs and func- tions and upon health in general. Probably the worst sufferers from this evil are well-to-do people of sedentary occupations — brain work- ers as distinguished from hand workers. Second. More food is served than can be eaten, and the excess is thrown away as table waste. Indeed, in many families in this country it is a matter of pride to furnish more food than is needed, a feeling which appears quite unreasonable to frugal Europeans, even those in equally comfortable circumstances. Third. The third form is that which occurs in the preparation of food materials for consumption. Thus, in removing the inedible mate- rial, as skin, seeds, etc., from fruits and vegetables, more or less of the edible portion is removed also, depending upon the care with which the work is done. The greatest loss from a pecuniary stand- point, however, is in the waste of animal foods in which the nutrients are in their costliest forms. The ' ' trimmings " of meat which are left with the butcher or removed in the kitchen frequently contain one-eighth of the nutritive ingredients of the material paid for. Part of such waste is inevitable, but much of the valuable nutrients might be saved if the materials were used for making soup. The more economical cuts of meats are those in which there is less waste of this, kind; in such cuts of meat as loin of beef, rib chops of lamb, and similar cuts, one-fifth the cost goes to pay for bone. Such cuts, therefore, should be avoided by those who wish to get the most actual nutriment for their money. Just where and among what classes of people the waste of food is greatest it is not possible to say, but there is certainly a great deal more of it in this country than in Europe. The worst sufferers from it are doubtless the poor, but the large body of people of moderate means, the intelligent, and fairly well-to-do wage- workers are guilty of errors in this regard. The common remark that ''the average Amer- ican family wastes as much food as a French family would live upon" is greatly exaggerated, but statistics show that there is considerable truth in it. In dietary studies conducted at a students' club in an Eastern college it was found that 10 to 14 per cent of the nutritive materials purchased were thrown away as kitchen or table waste, and yet the club members were trying to live as economically as was con- sistent with comfort. In private families the waste has been found to range from practically none to as high as 8 or 10 per cent, while in boarding houses, even where economy was sought, it has reached 10, and in individual instances 20 per cent; and in some public institu- tions where large numbers were fed it has been as high as 25 per cent and even higher. EKBORS IN COOKING. It is commonly remarked by those who study the conditions of liv- ing of people of limited means in different parts of the country that 142 47 for suhstautial improvement of their household economics two things are needed. They must be informed as to the high nutritive value of the cheaper foods as compared \vith the costlier kinds, and the meth- ods of cooking must be improved. A great deal of fuel is wasted in the preparation of food, and even then a great deal of the food is badly cooked. To replace dear food badly cooked by cheaper food well cooked is important for both health and purse. To make the table more attractive will be an efficient means for making the home Ufe more enjoyable. SUMMARY. Food has been briefly defined as ''that which taken into the body, either builds tissue or yields energy." In its btiilding function pro- tein is the most important iiigredient of food, as it is the basis of mus- cle, bone, and almost all the tissues and fluids of the body. Mineral matters are also needed in the body structure, though in smaller quan- tities. Protein, fats, and carbohydrates may any of them be burned in the body to produce heat or muscular energy, but for protein this is a less important and probably less usual function. The fats and carbohydrates, by being themselves used as fuel, leave the protein for its indispensable work of tissue forming. Not only the amounts of nutritive ingredients which a food contains, but also the proportions which can be digested and utilized by the body, determine the real nutritive value of a food material. As a general rule, carbohydrates are more completely digested and hence more fully available for use in the body than protein and fats, and protein of animal foods, as meat, fish, milk, and eggs, is more digest- ible than that of vegetable foods. Fats are probablly less digestible than most forms of protein and carbohydrates. In ordinary mixed diet the chief sources of protein are meat, fish, and milk among animal foods, and the cereals and legumes among vegetable foods. Beans, peas, and oatmeal are rich in protein and hence especially valuable food. About nine-ttmths of the fat in the ordinary diet is obtained from the animal foods, while the vegetable foods furnish approximately nine-tenths of the carbohydrates. Othf^r things being equal, foods furnishing nutrients wliich can be most easily and completely utilized by the body are the most desirable, since they will not bring unnecessary exertion to the various organs. Many kinds of food which in their natural state hold the most valuable nutrients in such form that the digestive juices can not easily work upon them are so changed by the heat of cooking that they become easily digf^stible. Thus the importance of proper cooking can hardly be overesti fruited. Things whi(;h please the palatt^ stinniiate th(^ Mow of the dige.stive juices; for this rea.son food should \hi made appetizing. An attractive diet pleases the aesthetic sense; hence reiinemcnt in food 48 habits is as desirable as in other phases of our daily Ufe. The sense of comfort and satisfaction produced by even the appearance of food well cooked and served is of indisputable value. Fortunately such satis- faction is within the reach of almost all. Among people who have the benefits of modern comfort and culture the palate revolts against a very simple and unvaried diet, and for this reason the nutrients are usually supplied from a variety of articles — some of animal, some of vegetable origin. With a varied diet it is also easier to secure the proper proportions of protein to fats and carbohy- drates. As the habits and conditions of individuals differ, so, too, their needs for nourishment differ, and their food should be adapted to their particular requirements. It has been estimated that an average man at moderately active labor, like a carpenter or mason, should have about 115 grams or 0.25 pound of available protein and sufficient fuel ingredients in addition to make the fuel value of the whole diet 3,400 calories, while a man at sedentary employment would be well nour- ished with 92 gramis or 0.20 pound of available protein and enough fats and carbohydrates in addition to yield 2,700 calories of energy. The demands are, however, variable, increasing or decreasing with increase or decrease of muscular work, or as other needs of the person change. Each person, too, should learn by experience what kinds of food yield him nourishment with the least discomfort, and should avoid those which do not "agree" with him. Too much food is as bad as too little and occasions a waste of energy and strength in the body as well as a waste of nutritive material. While in the case of some foods as purchased, notably meats, some waste is unavoidable, the pecuniary loss can be diminished, both by buying those kinds in which there is the least waste, and by utilizing more carefully than is ordinarily done portions of what is usually classed as refuse. Much of the waste may be avoided by careful plan- ning so as to provide a comfortable and appetizing meal in sufficient amount, but without excess. If strict economy is necessary, the dearer cuts of meat and the more expensive fruits and vegetables should be avoided. With reasonable care in cooking and serving, a pleasing and varied diet can be furnished at moderate cost. It should not be for- gotten that the real cheapness or dearness of a food material depends not only on its market price, but also on the cost of its digestible nutrients. It should always be remembered that "the ideal diet is that combination of foods which, while imposing the least burden on the body, supplies it with exactly sufficient material to meet its wants," and that any disregard of such a standard must inevitably pre- vent the best development of our powers. o DATE DUE OFfi^ f ?flPl i SUI ' M^ZZi i^i : .; ^,'^ ^ ?iMt m 1^ ■§ ' 01 IW Mi^y ^ ' i uvm DEMCO 38-296 lES Cgj^MBM MK.M,.^„.-. IPUI Atvz-ater At92 1910 /6-/^-yi Qu,