Effect of Variable Intake on Body Composition 117 



That body tissues can vary significantly in composition except 

 under extreme conditions is difficult to reconcile with present- 

 day knowledge of tissue composition. 



The experiments to be described here were undertaken in 

 an attempt to characterize the effects of high and low mineral 

 and protein intakes, in various combinations, upon the body 

 composition of the growing albino rat as determined by 

 direct whole body analysis. Previous work using this method 

 of approach has been concerned with single constituents and 

 not with the interrelationships of all of the components. The 

 data indicate little variability in composition for the collective 

 soft tissues of the body. The only intake-dependent relation- 

 ship that seems of significance is in the relative proportions 

 of skeleton to soft tissues. 



Experimental Methods 

 A. Animals and Diets 



Male weanling Sprague-Dawley strain rats were used in all 

 feeding experiments. Two groups of animals were used to 

 measure food consumption on the high and low protein diets. 

 In these experiments spill-proof feeding tunnels were used, 

 and the animals caged singly. The remaining groups of 

 animals were housed in units of four in steel wire cages with 

 open-mesh bottoms. Continuous access to unlimited quanti- 

 ties of food in open containers was allowed. Distilled water 

 was similarly offered from dropping bottles. All groups of 

 animals were allowed to grow for a period of 20-25 days. 

 This period of time was chosen as it allowed approximate 

 doubling of weight for the most slowly growing groups. 



The experimental diets were compounded using powdered 

 fat-free cow's milk (Starlac, The Borden Company), electro- 

 lyte and vitamin-free casein (Nutritional Biochemicals 

 Corporation, Cleveland), dextrose, a fat mixture composed of 

 equal parts of corn oil (Mazola Corn Oil, Corn Products Re- 

 fining Co., Argo, Illinois) and hydrogenated vegetable oil 

 (Crisco, Proctor and Gamble, Cincinnati, Ohio), and a salt 



