NUTRITIVE INGREDIENTS AND VALUES OF THE FOOD WE EAT. 671 



The Nutrient* of Foods and their Functions 

 in Nutrition. First, however, it may be well 

 to recapitulate very briefly some of the main 

 results of later research respecting the nutri- 

 tive ingredients of foods, and their work and 

 uses in nutrition. This is the more proper, 

 since the more lately ascertained facts have not 

 only added greatly to our knowledge, but the 

 older theories have thereby been materially 

 modified ; and, further, because the later views 

 have not yet become current in the English 

 language. 



We eat meat and fish, potatoes and bread, to 

 build up our bodies, repair their wastes, and 

 supply them with fuel for the production of 

 heat and force. In other words, our food 

 supplies, besides water and mineral substances, 

 several classes of nutrients, of which the most 

 important are albuminoids or proteids, carbo- 

 hydrates and fats, and whose functions are to 

 be transformed into the various tissues and 

 fluids of the body, muscle and fat, blood and 

 bone, and by their decomposition and con- 

 sumption to produce heat and force. 



Albuminoids, Proteids, or Protein Com- 

 pounds. These contain carbon, oxygen, hydro- 

 gen, and nitrogen, the latter element being char- 

 acteristic of albuminoids. Albuminoids occur 

 in plants, as in the gluten of wheat ; and in the 

 animal body, as in the fibrinogen and fibrino- 

 plastic substances of blood, in the fibrin of 

 muscle, in albumen (white) of eggs, and in the 

 casein (curd) of milk. 



The albuminoids are the most important of 

 the nutrients of foods. Not only do they share 

 in the formation of the fatty tissues and in the 

 supply of material for the production of animal 

 heat and muscular power, thus performing all 

 of the functions of the other food ingredients 

 in the body, but they also have a work of 

 their own in the building up of the nitrogen- 

 ous tissues, muscles, tendons, cartilage, etc., 

 in which none of the other ingredients can 

 share. 



Carbohydrates, of which we have familiar 

 examples in sugar, starch, and cellulose, differ 

 from the albuminoids in that they have no ni- 

 trogen. They have, according to the best ex- 

 perimental evidence, no share in the forma- 

 tion of nitrogenous tissues in the body. That 

 they are transformed into fats to any consider- 

 able extent is at least questionable. Their chief 

 use in food seems to be to supply fuel for the 

 production of animal heat, and very probably 

 of muscular energy. They also do a most use- 

 ful duty in preventing the consumption of al- 

 buminoids and fats, by being consumed them- 

 selves. They are very important constituents 

 of food, but less so than the albuminoids. 



Fats are familiar to us in the vegetable fats 

 and oils, as linseed and olive oils; in fat meat, 

 tallow and lard, and in butter, etc. Fats, like 

 carbohydrates, consist of carbon, oxygen, and 

 hydrogen, and are destitute of nitrogen. The 

 fats of food are stored in the body as fats, 

 transformed into carbohydrates, and serve as 



fuel to produce heat and probably muscular 

 force, but do not form nitrogenous tissue. They 

 are more valuable than the carbohydrates, be- 

 cause richer in carbon and hydrogen, the ele- 

 ments which give value to fuel, and because they 

 supply the body with fats. 



Besides the nutrients named above, there are 

 others of inferior but nevertheless not incon- 

 siderable importance in nutrition, as kreatin, 

 sarkin, inosite, and so on. The proportions of, 

 these are, however, so small and their functions 

 so little understood, that it is at present cus- 

 tomary to leave them out of account or group 

 them with the other nutrients in estimating 

 the nutritive values of foods. Classifying the 

 organic nutrients of food thus roughly, the 

 chief uses of each class in supplying the body 

 with material for its tissues and fluids, and for 

 the production of heat and muscular force, 

 may be briefly outlined as follows : 



Nutrients. Function! In Nutrition. 



ALBUMINOIDS, f A u re transformed into ALBUMINOIDS. 



^0^"' " SS 



Uerve for FUEL. 



CAKBOHYDBATES. Servo for FUEL. 



FATS. 



( Are transformed into FATS. 



< * u " CARBOHYDRATE--. 



| Serve for FUEL. 



Proportions of Nutrients in Different Foods. 

 As the functions of the nutritive ingredients 

 have become better understood, more and more 

 attention has naturally been devoted to the 

 investigation of the composition of foods, and 

 the nature and proportions of their various 

 constituents ; so that, although only the later 

 wprk has been done by methods fully in accord 

 with the demands of chemical and physiolog- 

 ical science as it now exists, yet a large amount 

 of reliable information has already accumulated. 

 Many hundreds of analyses of vegetable and 

 animal food products have been executed in 

 Europe, especially in Germany. In this country 

 the analytical investigation of this sort has not 

 until within a few years past been at all ex- 

 tensive, and that which has been done has 

 been confined almost exclusively to materials 

 used for feeding domestic animals. 



Under the auspices of the Smithsonian In- 

 stitution and the United States Fish Com- 

 mission, an investigation of the chemical com- 

 position and nutritive values of some of our 

 American foods has been undertaken in the 

 chemical laboratory of Wesleyan University, 

 Middletown, Connecticut, under the direction 

 of Professor W. O. Atwater. This work has 

 begun with analyses of fish, but ia being ex- 

 tended to other animal and to vegetable foods. 

 The research has been going on for some time, 

 and now includes chemical analyses of some 

 two hundred specimens of the flesh of fish, 

 oysters, lobsters, and other "fish-foods," with 

 a number of meats of various sorts, and some 

 vegetable products. Some of the results, along 

 with those of similar European products, are 

 given in the table herewith : 



