352 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



The data showing the relationship between the excess heat and the 

 fuel value of the intake, which are given in tables 249 and 250 (see 

 pages 336 and 338), vary considerably with the length of the experiment, 

 the total amount of the food intake, and the nature of the diet. While, 

 for lack of a better terminology, the values are designated as the "cost 

 of digestion", the use of such a term is distinctly misleading, as imply- 

 ing that this excess heat is waste heat. We are firmly convinced that 

 the excess heat produced from the ingestion of protein or carbohydrates, 

 like sugars, may not properly be considered as purely a waste process, 

 but that it is far more logical to consider it as a general stimulation of 

 all of the cells in preparation for the drafts of muscular activity. 



Our results give no basis for recommending an exclusively protein 

 diet or an exclusively sugar diet prior to severe muscular work. That 

 the presence of glycogen in the body has an important bearing on the 

 efficiency of the muscular system is, in general, we think, proved with- 

 out doubt. That any food substance that will contribute toward the 

 replenishment of a depleted glycogen store or will maintain this at a 

 high level is important in the preparation for muscular work, we like- 

 wise may consider as being thoroughly established. The formation of 

 glycogen from sugar is unquestionably proved; the formation of glyco- 

 gen or sugars from protein is likewise demonstrated ; but there is as yet 

 no evidence that sugar is formed from fat. It follows, therefore, that 

 diets preceding muscular work should contain liberal quantities of 

 carbohydrates or protein, although our evidence does not allow us to 

 determine which is the more important, the furnishing of glycogen or 

 the normal stimulus to the body. There is no question but that protein 

 is a more prolonged stimulus to the metabolism than carbohydrate. 

 On the other hand, in the digestion of protein extra work is thrown 

 upon the organs of excretion. Too much significance may be given to 

 this, but nevertheless, since the ingestion of carbohydrates does not 

 require such work, there appears to be a legitimate ground for ques- 

 tioning whether an excessive protein diet or an excessive carbohy- 

 drate diet would be the more desirable to provide a glycogen storage 

 as preparation for muscular work. The value of large diets of either 

 protein, carbohydrate, or mixed nutrients to replenish the glycogen 

 depots and stimulate the whole body to cellular activity is plainly 

 shown by our experiments. The practical application of this fact 

 would seem to lie more particularly in the preparation for those bodily 

 activities calling for considerable muscular work. 



