CLASSIFICATION OF FOODSTUFFS 33 



Now it is self-evident that we are continually voiding waste products, 

 urea and very many other substances in the urine, carbon dioxide and 

 water-vapor in the breath, and various items of waste in the sweat 

 and in the feces. Furthermore, despite his rapid and continual losst 

 of substance, when we are adult we remain tolerably constant in weight 

 and composition, that is, if we are healthy and neither becoming 

 emaciated nor growing fat. It follows that, as a general rule, we must 

 be taking in from without, not only just as much total substance as we 

 are losing daily in these various ways, but also just as much of each of 

 the individual elements, nitrogen, carbon and so forth, as we are daily 

 voiding. This intake of elements constitutes the act of feeding, and 

 the forms in which we take in these elements are our Foods. 



THE CLASSIFICATION OF FOODSTUFFS. 



As has been stated, our articles of diet are more complex than those 

 of the plants. Plants can utilize the carbon in carbon dioxide, but we, 

 in order to replace our carbon-waste, must use some more complex 

 compound of carbon, in fact, as our daily experience reveals, either a 

 carbohydrate (sugars, starches, etc.), a fat, or a protein. Otherwise 

 we inevitably suffer from carbon starvation. Plants, again, can derive 

 nitrogen from nitrates in the soil, but we, more dependent, can only 

 derive the nitrogen which we need from preformed protein. Mineral 

 and other inorganic foods we only utilize to replace or provide mineral 

 or inorganic constituents of our tissues ; we cannot utilize them directly 

 to build up carbohydrates or fats as plants can. Our foodstuffs fall, 

 therefore, into four main classes, to wit : 



1. The Inorganic Foods, such as water and mineral salts. 



2. The Carbohydrates, such as the sugars and starches. 



3. The Fats. 



4. The Proteins. 



To which must be added certain accessory articles of diet, to which 

 frequent reference will be made, which are of vital importance to the 

 maintenance and furtherance of life, but yet do not necessarily fall 

 within any of the above-mentioned classes. 



