INCREASE 197 



Fattening. It was shown (Chapter VIII.) that, under 

 certain conditions, body fat can be formed from all or any 

 of the digestible nutrients fat, protein, and carbohydrates 

 of the food. The physiological heat values l of these con- 

 stituents are 9^4 kt , 4*93 kt, and 376 kt. per lb., respectively. 

 It might be expected that they would bear much the same 

 relation as fat formers, i.e. that 2-5 Ibs. of starch, and 1*9 Ibs. 

 of protein would each produce the same amount of body fat as 

 i lb. of fat in the food. This expectation has been entirely 

 justified as regards the former, but not as regards the latter. 



Calculating from the chemical composition of the two 

 substances, Henneberg inferred that 51*4 Ibs. of fat could be 

 formed from 100 Ibs. of protein. This relation commonly 

 called Henneberg's number was generally assumed in the 

 older experiments. Further investigation has shown, how- 

 ever, that it is too high. Body fat is formed from the protein 

 of the food only when the latter is present in excess of the 

 requirements for other purposes. When the transformation 

 does occur, a considerable part of the protein is oxidised, and 

 not more than 39 parts of fat are formed from 100 parts of 

 that substance, i.e. 2*56 parts of protein are required to pro- 

 duce the same increase as i part of fat in the food. These 

 quantities 2-56 parts of protein, 2-5 parts of starch, and 

 i part of fat are, therefore, said to be equivalent for the 

 production of fattening increase. Put in the other way, 

 i part of starch is equivalent to o - 4 part of fat, and i part 

 of protein to 0*39 part of fat. 



Referring to the composition of the fattening increase 

 (p. 189), it will be seen that, on the average, it contains about 

 7 per cent, of protein and 70 per cent, of fat. It might be 

 expected, therefore, that an allowance of 0*07 lb. of the 

 former, and 0*7 lb. of the latter, in addition to an adequate 

 maintenance ration, would be sufficient to provide for an 

 increase of i lb. This is approximately true when the animals 

 are in a very lean condition, but the rate of increase for food 

 consumed gradually diminishes as the animals become fatter. 



Experiments in the respiration chamber show that fattening 



1 Some fats are of lower value (cf. Chapters IX. and XIII.). 



