Effect of Variable Intake on Body Composition 129 



The rationale for the use of the latter standard has been dis- 

 cussed in detail elsewhere (Cotlove et al., 1951). While such a 

 reference point is essential for evaluation of acute shifts of 

 water and electrolytes in tissues, it may not be equally 

 applicable where the growth of a complex of tissues is in- 

 volved. In this latter situation it is essential that the relative 

 gain or loss of a substance in question be examined in regard 

 to a number of reference standards, as has been done here (see 

 Results). When the change in any constituent is consistent in 

 direction, regardless of the reference basis, it is probably a 

 real one, as has been noted above. However, when the change 

 is in one direction on one basis and in the opposite on another, 

 the question of gain or loss is difficult to assess. An example of 

 this from the current data is found in the change in potassium 

 content with change in protein intake in the animals on the 

 low electrolyte diets. The high-protein-fed animals were 

 larger and contained more potassium on an absolute basis. 

 When calculated per kilogram of fat-free body the potassium 

 concentrations were equal, but on a litre of water basis the 

 potassium was greater in the low protein group. Again, 

 referring this ion to fat-free dry solids, the high-protein-fed 

 animals would seem to have the highest content. For the 

 purposes of nutritional evaluation, it is valid to calculate 

 constituents as per unit of whole body inclusive of fat. When 

 this is done, an even greater number of permutations and 

 combinations can be found with regard to relative contents 

 of all substances. Until more is known concerning the distri- 

 bution, function and relationships of protein and electrolytes 

 in tissues, it would seem advisable to emphasize only those 

 changes which are relatively consistent. 



When the present data are considered on this basis, the 

 composition of the body with regard to water, protein and ash 

 is the same despite variation of the components of the intake. 

 The whole body may be smaller or larger as limited by the 

 availability of certain crucial nutriments but its relative 

 composition remains unchanged. Only the relative size of the 

 skeletal mass in relation to soft tissue seems to be significantly 



AGEING — IV — 5 



