NUTRITIVE VALUE OF FISH AND SHELLFISH 527 



IL— FISH AND SHELLFISH AS A SOURCE OF PROTEIN 



By Donald K. Tressler, Industrial Felloiv, Mellon Institute of Industrial 



Research, Universiti] of Pittsburgh 



INTRODUCTION 



Protein is one of the most important components of our diet. Fats 

 and carbohydrates are primarily energy-yielding foods, whereas pro- 

 teins are not only sources of energy but are tissue-builders as well. 

 Our bodies form the proteins characteristic of our own tissues; they 

 can not build them up from simple inorganic substances but must 

 depend upon the digestion products obtained from the food. Neither 

 the growth of the young nor the satisfactory nutrition of adidts can 

 take place without an adequate source of proteins in the diet. Fur- 

 ther, recent studies in nutrition have pointed out the danger of at- 

 tempting to live over the entire span of adult life on a diet containing 

 just sufficient proteins of good quality to support growth at approxi- 

 mately the maximum rate to the full adult size. A generous protem 

 ingestion during our entire lives is required to maintain optimal vigor 

 for the longest possible period. 



An examination of the tables given in the preceding section indi- 

 cates that fish resemble meats in containing a high percentage of pro- 

 tein. Live crabs, lobsters, shrimp, scallops, mussels, clams, and 

 oysters contain much calcareous matter in their shells and also con- 

 tain much water ; for these reasons their protein content is apparently 

 much lower, but when the analyses of water-free substance of the 

 edible portion of these shellfishes is considered it is seen that its pro- 

 tein content is also high. 



Near the seashore and in the markets of the large cities where fish 

 may be purchased cheaply in season they constitute a low-priced 

 source of protein. Well-cooked fish are delicious and offer a welcome 

 change from a steady diet of meat. Protein purchased in the form 

 of crabs, lobsters, scallops, clams, and. oysters at the usual prices of 

 these shellfish is more expensive. However, these mollusks and crus- 

 taceans have other nutritive values and should not be omitted from 

 well-planned diets. 



Inasmuch as proteinaceous foods are so essential for the w^ell-being 

 of man, and as fish and shellfish contain much protein, a considera- 

 tion of the nutritive value of their proteins should be made if these 

 foods are to be given their proper place in the diet. 



CHARACTERISTICS OF PROTEIN REQUIRED FOR THE NUTRITION OF 



MAN 



Proteins, whether found in plants or animals, are complex com- 

 pounds of high molecular weight built up of a number of relatively 

 simple substances called amino acids, which are combined in various 

 proportions. The amino acids of common proteins include the 

 following: Glycine, alanine, valine, leucine, phenylalanine, tyrosine, 

 serine, cystine, aspartic acid, glutamic acid, ornithine, arginine, 

 lysine, histidine, proline, tiyptophane, and oxyproline. 



During the digestion of a protein it is split up into these amino 

 acids or into combinations of a few of them called peptids. The 

 amino acids and peptids are absorbed by the blood stream; those 

 required for the building of tissues are so utilized, and those left 



