1-i The Composition ''and Food Vdhre of Bread. 



the very short period of two days, but their reliability is 

 increased by the fact that they all agree among themselves, and 

 the figures may therefore be accepted with some considerable 

 degree of certainty. Finally, it should be explained that the 

 energy digested is determined by subtracting (from the heat 

 given out by burning a known weight of the food) the sum of 

 the heat given out by burning the dry matter of the urine and 

 of the faeces excreted as the result of eating that weight of 

 food, the amount of heat in each case being measured by the 

 number of degrees of temperature through which a known 

 weight of water is warmed. 



Turning now to the figures themselves, it is at once evident 

 that there is a close connection between the grade of the flour 

 and the digestibility of its protein and enei'gy. These con- 

 stituents of the flours of commercially higher grades are far 

 more completely digested than the same constituents of the 

 low^er grade flours. In other words, the more husk a flour 

 contains the lower the proportion of its protein and energy 

 digested and absorbed into the blood, to be distributed to the 

 various tissues of the body. The differences in digestibility 

 are so large that they cannot be ignored, as is so often the case, 

 in estimating the food value of the different grades of flour, 



I have calculated below, from the figures given in Tables III. 

 and IV., the actual amounts of protein and energy which could 

 become available to the tissues of the body from the consump- 

 tion of the daily ration of bread and flour shown in Table I. 

 Assuming that all the flour included in this ration, both as 

 bread and in other forms, is straight grade flour, then of the 63 

 grams of protein it contains, 89 per cent., i.e., 5G grams, would 

 be digestible. If, on the other hand, all the flour in the diet 

 were wholemeal flour, the diet would contain rather more 

 protein, as shown in Table III. The exact amount would be 

 ()3 X ll*3-=-10*6, i.e., 67 grams. Of this only 76 per cent., i.e., 

 51 grams, would be digestible. Thus the average w^orkman, 

 if he fed on wholemeal bread, would certainly eat a little 

 more protein every day, but he would really digest consider- 

 ably less, in fact, 5 grams, or nearly a quarter of an ounce less. 

 Since it is only the protein which is digested and absorbed that 

 benefits the body, the replacement of white bread by whole- 

 meal bread in the diet of the people would rather decrease 

 than increase the available protein of the diet. Exactly the 

 same result appears when the energy values are worked out. 

 Replacement of white bread by wholemeal bread would 

 reduce the available energy of the diet by 170 units per head 

 per day. 



The experiments quoted above were all carried out in 

 America, and to the best of my knowledge no experiments on 



