194 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



tity of foods, these changing with the season and geographical location. 

 Furthermore, even with individuals who live a regular life, the muscular 

 activity varies considerably. With so great changes in the factors 

 influencing the body-weight, this practically constant balance between 

 food intake and consumption of material in the body, with no great 

 storage of material or drafts upon previously stored material, leads one 

 to conclude that the majority of individuals so select their diet as to 

 meet their physiological needs, as far as the total fuel content of the 

 food is concerned. 



Since in this monograph the factor of growth is not to be considered, 

 it is only necessary to discuss the food requirement for keeping the body 

 in condition for the needs of daily hfe. The body-cells are continually 

 undergoing metamorphosis and disintegration and hence must be 

 repaired. In addition there are temporary drafts upon stored .body- 

 material. This is obvious when one considers that the combustion of 

 material is continuous, while the food intake is only intermittent. 

 Many individuals take food only twice a day; in the interim, particu- 

 larly in the early morning hours, the combustion of material in the body 

 must be largely that which has been previously deposited in the form 

 of either glycogen or fat. With exercise these drafts upon body- 

 material may be even greater, but the compensation is rapid; in fact, 

 after severe exercise large amounts of food are usually consumed, so 

 that the delicate balance between intake and output is even then main- 

 tained. 



TRANSITORY VARIATIONS IN BODY-WEIGHT. 



In judging of the adequacy or inadequacy of a diet, transitory varia- 

 tions in body-weight should not be emphasized unduly. The body 

 contains a large proportion of water, which may be very rapidly lost or 

 gained. In pathological cases, with edema, very large amounts of 

 water may be stored in the body. With normal individuals, the most 

 striking examples of variations in weight which are without significance 

 as indicating actual loss of body-tissue occur with athletes during severe 

 muscular exercise. Professor William G. Anderson,^ of the Yale Uni- 

 versity Gymnasium, states that a football player in 1 hour and 10 

 minutes of exercise lost 6.4 kg. It is not uncommon for Marathon 

 runners in 3 hours of running to lose 3.9 kg., while a member of a college 

 boat crew in a 22-niinute race is known to have lost 2.5 kg. An analy- 

 sis of this loss, based upon the known metabolic activities during severe 

 muscular work, shows clearly that in so short a period as 22 minutes it 

 would be utterly impossible to have disintegrated 2.5 kg. of either pro- 

 tein, fat, or carbohydrate. In experiments with a bicycle rider riding 

 to the limit of human endurance, with a runner, or with a man walking, 

 it has been found that 200 grams of carbon dioxide per hour represent 



^Benedict and Joslin, Carnegie Inst. Wash. Pub. No. 176, 1912, p. 96. 



