DIFFERENCES IN NUTRITIONAL REQUIREMENTS 



313 



ment of these signs (40, 58, 59). Criteria 

 of other aspects of the nutritional status 

 are also being subjected to a more searching 

 analysis and reevaluation. Even such an 

 apparently well-estabHshed base as the 

 height-weight relationship is being questioned 

 as a rehable reference point. There are indi- 

 cations that, if methods could be developed 

 for the determination of the amount of fat 

 in the body, then a better basis could be 

 provided for evaluating obesity. Valid in- 

 formation on the body fat content would be 

 especially important for individuals who lead 

 sedentary lives. Under such circumstances, 

 the gross weight might be within the normal 

 range according to the height-weight tables, 

 yet the individual might have undergone 

 a profound physiological change. Much of 

 his original muscle tissue might have been 

 replaced by fat. 



The imphcations of such a change from 

 a nutritional standpoint is becoming clearer 

 with the accumulation of data provided by 

 animal experiments and chnical research. 

 The animal studies concerned with the in- 

 fluence of the rate of growth and the adult 

 weight agree in the following conclusions: 

 (1) Those animals that grow at a slow rate 

 because of a caloric restriction, live longer 

 than the controls fed ad libitum. (2) The 

 slower-growing animals show a lower in- 

 cidence of tumor growths. (3) The caloric 

 restriction necessary to produce these 

 changes is very drastic (12, 43). Insurance 

 statistics indicate that overweight in man 

 is associated with higher morbidity and mor- 

 taUty. 



The sedentary individual is not only in- 

 cUned to an accumulation of adipose tissue, 

 but exhibits a concomitant decrease in phys- 

 ical "fitness." His endurance for physical 

 exertion is reduced. There are many sug- 

 gestions that with this decrease in physical 

 "fitness" there is a corresponding decrease 

 in the abihty to withstand various physio- 

 logical stresses such as infectious disease, 

 physical trauma, etc. (16). It must be rec- 

 ognized that at present this thesis is not 



supported by adequate evidence; it is one 

 area in which rigorous research is urgently 

 needed. The problems are important for 

 the submariner, since his is a relatively 

 sedentary existence, and, unless special 

 measures are taken, some of the debihtating 

 changes may occur prematurely in liim. 



Differences in Nutritional 

 Requirements 



The need for additional nutritional re- 

 search becomes more apparent as the dif- 

 ferences between man and animals are more 

 clearly recognized. Some of these differ- 

 ences will be mentioned in order to em- 

 phasize the caution needed in applying the 

 results of animal experiments in human be- 

 ings. Marked differences such as those that 

 exist between man and the herbivores are 

 readily recognized and accepted. For ex- 

 ample, it is well known that the bacteiial 

 flora of the cow's digestive tract will syn- 

 thesize practically all of the vitamins of the 

 B complex. This makes cattle independent 

 of a dietary source of these vitamins. 



There are marked differences in the re- 

 quirements for vitamins and amino acids 

 among the various species of animals. 

 When the differences between species are 

 small, there is a pronounced tendency to 

 translate the findings as indicating identity 

 in requirements and physiological responses. 

 The very existence of spontaneous food al- 

 lergies in some individuals and their absence 

 in animals should be a sufficient deterrent 

 to those who consider animal experiments an 

 adequate substitute for studies on normal 

 human beings. Finallj^, it should be em- 

 phasized that almost all nutritional work 

 is done with animals that have been highly 

 inbred so that the genetic variability was 

 practically ehminated. Such work is neces- 

 sary for a study of the infl.uence of separate 

 factors. However, any group of men is very 

 heterogenous, even when every effort is made 

 to choose only those who most closely fit a 

 narrow pattern of age, race, mode of hfe, 

 etc.; under such conditions "general laws" 



