312 



DIET 



are intmately linked to the progress of the 

 general science of nutrition. Naval support 

 for research on the broad, fundamental ques- 

 tions of human nutrition, parallehng work on 

 the immediate and narrow problems, will 

 in the long run pay dividends. 



In a national emergency, there is an ur- 

 gent demand for information on the rela- 

 tionship between fitness and diet, but there 

 is httle time or facihty for a thorough study 

 of the problem. In peace, there is a tend- 

 encj^ to relapse into routine activities and 

 limit research to a minimum. In some areas 

 of the study of man, the potential contribu- 

 tion of research is ignored entirely. This 

 seems largely to be the case as far as sub- 

 marine nutrition is concerned. 



Trends in Nutritional Research 



In its relatively short history, nutritional 

 research has at various times changed its 

 course rather abruptly and followed narrow 

 channels which were almost completely 

 abandoned in the next phase. Most of the 

 early work in this field was devoted to a 

 study of food as the fuel supplying the 

 bodj^'s demands for energy. Toward the 

 end of the last century various types of 

 calorimeters were constructed by means of 

 which laws of energy transformation were 

 studied in living organisms. This work in- 

 volved essentially the adaptation to nutri- 

 tional studies of various pieces of equipment 

 and experimental techniques which were al- 

 ready being used in other scientific fields. 



At about the same time that these studies 

 were going on, Kjeldahl developed a rela- 

 tively simple means for the determination 

 of nitrogen in organic substances. Nitrogen 

 is the element which characterizes proteins. 

 The Kjeldahl procedure thus opened the way 

 for extensive studies on this important die- 

 tary constituent. 



Studies were also made on the more com- 

 mon minerals such as iron, sodium, potas- 

 sium, calcium, and phosphorus, since the 

 chemical and physical methods of analysis 

 available at that time could easily be used 



for such purposes. The study of those min- 

 erals that are required by the body in smaller 

 amounts had to await the development of 

 sensitive chemical tests and further progress 

 in the general field of nutrition. 



The vitamin field showed its greatest ad- 

 vances when it became possible to use puri- 

 fied foodstuffs that were adequate in all 

 respects but that of vitamins. To rations 

 which were practically devoid of any vi- 

 tamins were added the purified fractions of 

 those foods which were particularly potent 

 in the substance under investigation. By 

 repeated physical and chemical fractiona- 

 tion, many vitamins were finally isolated in 

 pure form. As each new vitamin became 

 available, the recognition of additional ones 

 was that much easier. 



Some of the microbiological techniques 

 developed for vitamin assays have proved 

 very amenable to the study of individual 

 amino acids. The development of this tech- 

 nique, together with a number of other fac- 

 tors, has resulted in a marked resurgence of 

 interest in the protein field. The availa- 

 bihty of various isotopes will complement 

 and modify the stream of nutritional 

 research in the future. 



As the various nutritional factors have 

 been uncovered, their requirements by hu- 

 man beings became a matter of concern 

 both from a quahtative and a quantitative 

 standpoint. It has only been within very 

 recent times that well-controlled studies on 

 human subjects were possible. Previous to 

 that, what httle work was done in this area 

 was hmited to field surv^eys. Under such 

 conditions, the criteria used in assessing the 

 nutritional status of the subjects are of con- 

 siderable importance. With time, the cri- 

 teria originally set up as bench marks for 

 the various deficiency states have undergone 

 considerable revision. 



Corneal vascularization, cheilosis, rhag- 

 ades, and related symptoms have been con- 

 sidered as pathognomic of a riboflavin de- 

 ficiency. Now it is recognized that other 

 factors may be responsible for the develop- 



