Absorption, Metabolism, and the Diet - 345 



inorganic foods were not considered, simply 

 because these substances do not supply en- 

 ergy to the body. But there are a number of 

 essential inorganic compounds in the proto- 

 plasm; and unless the intake and output of 

 these substances are balanced, the body can- 

 not maintain its normal functions. 



Inorganic Requirements. The water balance 

 drate, and only the nonessential amino acids of the body is very important. Each day an 

 (p. 136) can be derived from nonprotein average individual loses about 2000 cc of 



sues lack carbohydrates to oxidize simulta- 

 neously. 



In the body considerable interconversion 

 takes place among the foodstuffs (p. 156). 

 Many amino acids can be converted to glu- 

 cose; and carbohydrates can be converted to 

 fat. However, there is only a very limited 

 conversion of fatty materials into carbohy- 



foods. Most natural foods are mixtures con- 

 taining some of each kind of the main or- 

 ganic nutrients (Table 18-1). Consequently 

 the problem of meeting the energy require- 

 ments of the body is largely a matter of get- 

 ting a sufficient quantity of food. 



water via the urine, sweat, feces, and expired 

 air. These losses must be restored very regu- 

 larly, or else the tissues become seriously de- 

 hydrated. The body dies of "thirst" more 

 quickly than from starvation in the ordinary 

 sense. 



Table 18-1— Analysis of Some Common Foods 

 (Percentage by Weight) 



Starvation. When the total consumption of 

 food is inadequate to meet the energy ex- 

 penditure, the body begins to sacrifice its 

 existing fund of organic materials. First to 

 go are the carbohydrate stores, mainly the 

 glycogen of the liver and muscles. Simultane- 

 ously fat is gradually withdrawn from the 

 adipose tissues. When the fat and carbohy- 

 drate reserves have been exhausted, the body 

 begins to consume its own essential struc- 

 tural components — the proteins, phospho- 

 lipids, etc., in the tissues of the less essential 

 organs of the body. Finally the protoplasmic 

 constituents of the essential organs (brain, 

 spinal cord, and heart) are drawn upon; but 

 when this occurs, death rapidly becomes in- 

 evitable. 



Constructive Metabolism: Essential Kinds 

 of Foods. From an energy point of view the 



The replenishment of salts is also impor- 

 tant. The body loses about 30 grams of as- 

 sorted minerals each day via the urine, sweat, 

 and feces. Most natural foods contain ap- 

 proximately the proper proportions of the 

 protoplasmic salts (p. 75), although plant 

 foods are generally low in NaCl. Conse- 

 quently man has learned to use the crystal- 

 line form of this salt to supplement his own 

 diet and the diets of his domestic animals. 



Severe muscular work carried on in a hot 

 environment induces a very large loss of salts 

 (and water) via the perspiration. When this 

 condition is carried to an extreme, the worker 

 develops "miner's cramp," a painful spasm 

 involving a large part of the musculature. 

 Such workers are rabidly thirsty, but to 

 drink water only aggravates the condition by 

 increasing the flow of sweat and accelerating 



