THE ABSORPTION AND USE OF FOODS 511 



therefore, fat, and his diet usually consists largely of this sub- 

 stance. He is thus confronted with the ever-present possibility 

 of developing acidosis. As a matter of fact sooner or later 

 practically every pronounced diabetic has this experience. Fatal 

 acidosis is the recognized cause of death in the disease. 



Principles of Dietetics. From the various considerations 

 presented above we may summarize the general rule that the 

 choice of food should be such as to yield sufficient protein for the 

 Body's protein requirement, without containing an amount so 

 excessive as to throw an undue burden on the excretory organs; 

 that the amount of fat should be somewhat limited; and that 

 enough carbohydrate should be added to bring the sum total 

 up to the Body's energy requirement; finally, that the most ap- 

 petizing foods obtainable within a reasonable limit of cost should 

 be selected. Fortunately for the well-being of the race, mankind 

 has always selected just such a diet under no other guidance than 

 his appetite and his means, and these, to a healthy person, make 

 trustworthy guides, so long as they are accompanied by temper- 

 ance as a third. 



The importance of dietetics as a science is chiefly in connection 

 with the feeding of the sick, or providing for the maintenance of 

 large numbers of individuals, as in armies or public institutions, 

 where a slight error in selecting food, in greater amounts, or at 

 greater cost than needed, amounts in the aggregate to a very large 

 waste. 



The Maintenance of Constant Weight. It is the experience of 

 most adults that during periods of unbroken health the body 

 weight remains practically unchanged day in and day out. It is 

 clear that this condition depends on the maintenance of an exact 

 balance between the intake and outgo of the Body, since if more 

 is taken in than is given out there must be a gain in weight, and 

 vice versa. It is customary to consider the question of weight 

 maintenance under three heads : water equilibrium, nitrogen equilib- 

 rium, and carbon equilibrium. 



Water Equilibrium. For a Body to be in water. equilibrium 

 the amount of water lost per day must be exactly replaced by the 

 amount drunk. In large measure the sudden and transient 

 changes of weight which occur are due to upsets of water equi- 

 librium. Any violent exercise in hot weather reduces the weight 



