Diet as a Factor in Length of Life and in 



Structure and Composition of Tissues 



of the Rat with Aging 



By Mildred Adams 



Human Nutrition Research Division, Agricultural Research Service 



Early investigations with the laboratory rat as 

 experimental animal have dealt with nutritional 

 factors important for normal growth and develop- 

 ment of the young animal, and have provided 

 much information of basic importance to human 

 nutrition. In recent years, increasing emphasis 

 has been placed on the need for information con- 

 cerning the requirements of adult animals at 

 various stages of their lifespan. 



In this laboratory, investigations have been 

 underway for several years to determine the 

 influence of various dietary combinations on the 

 length of life and on the appearance of changes in 

 the structure and composition of tissues of the 

 rat. A preliminary report (39) 3 from this labora- 

 tory has indicated that the substitution of cooked 

 dried egg for 25 percent of a nutritionally adequate 

 basal diet accelerated development of degenera- 

 tive changes in tissues of the adult rat. When 

 the diet consisted of 100 percent whole egg, the 

 tissue changes observed were less severe and 

 occurred later in life, suggesting that an imbalance 

 of nutrients rather than egg itself may have been 

 responsible for the adverse results with the diet 

 containing 25 percent egg. 



In this publication are reported results of ex- 

 tensive investigations using the rat as the experi- 



mental animal and dealing with the influence of 

 diet on survival and some of the factors, including 

 diet, that may affect the presence or absence of 

 pathological lesions and the size and proximate 

 composition of selected organs. Included also are 

 results showing the influence of age and diet on 

 cholesterol and on various protein fractions in the 

 blood serum. 



The majority of the experimental diets were 

 modifications of a relatively simple diet composed 

 chiefly of semipurified components. In one group 

 of diets, protein and fat were varied by replacing 

 20 to 25 percent of the semipurified diet with egg, 

 milk, beef, or peanut butter. In a second group 

 of diets, the source and level of protein remained 

 constant but the kind and level of fat varied. 

 The fats were hydrogenated vegetable oil (HVO), 

 lard, and butter; the levels were 8 and 16 percent. 

 In addition, limited data are reported on the effect 

 of supplementing the diet containing 25 percent 

 egg with various B vitamins alone or in combina- 

 tion. The results of feeding diets containing rela- 

 tively high levels of egg yolk or egg white or 

 consisting solely of whole egg or egg yolk are also 

 included. 



3 Italic numbers in parentheses refer to Literature Cited, 

 p. 93. 



Experimental 



Description and Management of Animals 



A strain of rats (BHE) developed in this labora- 

 tory by crossing Albino (Yale strain obtained from 

 Columbia University) and black and white hooded 

 rats (Pennsylvania State College) served as the 

 chief source of the experimental animals. The 



litters included white, black, or black and white 

 rats. The parent stock animals were raised on a 

 standard pelleted ration 4 that is employed in our 

 breeding laboratories and has been found to be 

 efficient for growth, reproduction, and lactation. 



4 Animal Foundation Laboratory Diet, Standard Brands, 

 Inc., N.Y. 



