532 U. >S. BUREAU OF FISHERIES 



acids). The nutritive value of any protein, depends upon tiie quan- 

 tity and quality of tliese amino acids which it yields on digestion. 



Only a few of the proteins of fish and shellfish have been analyzed 

 for their content of the individual amino acids. From the available 

 data the following conclusions may be drawn: 



1. The proteins of fishes, scallops, and whales are complete, viz, 

 they contain all of the amino acids required for the growth and 

 maintenance of the human body. They are lacking in only one 

 amino acid — glycine — which can be obtained by the body by the 

 splitting of other amino acids; many investigators have demon- 

 strated that its presence in food is nonessential for proper nutrition. 



2. The amino acid composition of the proteins of other shellfish 

 has not been determined. 



3. The proteins of the fishes, scallops, and whales, which have 

 been analyzed for theii' amino acid content, have been shown to 

 be high in tyrosine, lysine, tryptophane, arginine, and histidine, 

 the amino acids which have been demonstrated as being required 

 in considerable quantities by the human body for growth and main- 

 tenance. 



4. The presence of a high percentage of lysine, histidine, and 

 arginine is particularly noteworthy, as these amino acids are deficient 

 in most vegetable proteins. Because of this fish and shellfish may 

 be served as the principal dish of a meal consisting largely of fruits 

 and vegetables v/ith the assurance that the fish proteins wiU com- 

 pletely supplement the vegetable proteins. 



5. The proteins of fish and shellfish are superior to most vegetable 

 proteins and equal to most meat proteins in nutritive qualities. 



III. OILS AND FATS FROM FISH AND SHELLFISH 



By Arthur D. Holmes, E. L. Patch Co., formerly specialist in charge of nutri- 

 tion experiments, Office of Home Economics, States Relations Service, United 

 States Department of Agriculture 



The dietary value of fish oils, like that of fats and oik obtained 

 from land annuals and plants, depends on a number of factors, the 

 principal ones being their composition or nature, digestibihty, and 

 vitamin content. 



COMPOSITION 



Considered from a chemical standpoint, the edible fats and oils 

 consists chiefly of glycerides of fatty acids; or, in other words, they 

 are compounds of glycerin and fatty acids, and, as every one knows, 

 when fats are saponified (made into soaps) one obtains soap (which 

 is a mineral salt of fatty acid) and glycerin as a by-product. 



The fatty acids most commonly occurring in the edible fats and 

 oils are oleic, linolic, palmitic, and stearic. These fatty acids differ 

 from one another principally as regards chemical composition and 

 the temperature at which they melt. The difference in the physical 

 condition of fats is largely due to this fact. 



Referring briefly to the above four fatty acids, the chemist would 

 say that the de^-ee of saturation and the melthig point increase as 

 one progresses in the series. In practical terms this means that 

 fats such as olive, peanut, and cottonseed oils, which contain a high 

 percentage of the glyceride of oleic acid, would become rancid more 



