Discussion 137 



Wallace: Can you change them by feeding them different diets? 

 Kennedy: After weaning this has no effect. I have increased the con- 

 centration of protein in our stock diet, which is usually 13 per cent, to as 

 high as 30 per cent, which is about what rat milk contains, without signi- 

 ficantly changing the growth rates of the large or the small weanlings. 

 We have not tried to change the diet of sucklings. 



Widdoivson : It would be most interesting to give some rats in a litter 

 electrolyte and protein supplements by stomach tube from the day of 

 birth omvards, and allow the mother to suckle the whole litter so that 

 some would get a higher protein and electrolyte intake than others. 

 Analysis of the bodies at three weeks of age might show much bigger 

 differences than those reported by Prof. Wallace for his older rats. 



Talbot: When you give a high as contrasted to a low protein intake, 

 how much protein do you give the rats per day relative to their absolute 

 growth increment? 



Wallace: I suppose that you are referring to the question of "feed 

 efficiency" — the relation of grams of food consumed to grams of weight 

 gained. This was 1-81 g. food per gram gain of weight for the high- 

 protein-fed animals and 2-51 g. consumed per g. of gain for the low 

 protein group. Thus the low protein group were less efficient in this 

 regard. If gain of weight per gram of protein consumed is calculated 

 the values are 0-41 g. per g. gain and • 30 g. per g. gain for the high and 

 low protein groups respectively. The high protein animals, however, 

 have a greater gain of protein per unit of weight gain. 



Kennedy : In the two curves you showed us with 100 per cent difference 

 in concentration of protein, there was nothing like 100 per cent differ- 

 ence in growth. Therefore it seems to me that the feed efficiency must 

 have been in favour of the low protein diet. 



Wallace: One of our reasons for doing this type of experiment was to 

 find out whether or not we could rely on balance measurements to meas- 

 ure the composition of growth. I think that the answer is a negative one. 

 Except for change in body fat content, the composition of the body of 

 the growing individual remains relatively constant over the periods in 

 which it is feasible to carry out such measurements. There are probably 

 extreme experimental conditions which do change body composition but 

 I do not believe that one can change lean body composition significantly 

 by changing the plane of protein intake. One can probably determine 

 more accurately the composition of growth by dilution techniques than 

 by the balance method. 



McCance : What would be the effect of change in diet on electrolytes in 

 the body? Our conclusion at the moment is that it has little effect on 

 the composition of the cell. 



Wallace: We cannot change the electrolytes in the cell; we can only 

 change the amount in bone. Muscle can be made to grow faster or bigger, 

 but its composition in terms of electrolytes cannot be altered. 



Heller : Our experience is that you have to decrease the protein content 

 of the diet very considerably to produce changes in body composition. 

 We have recently been feeding weanling rats on cassava flour and African 

 plantains, that is to say on diets that produce kwashiorkor in infants. 



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