Comparative digestibility of wholemeal and white breads and the effect of the degree of fineness of grinding on the former

Abstract

1. Loaves were baked from three types of wheaten flour made from the same grist; a straight run white flour of 73% extraction, a finely ground wholemeal (100% extraction) and a medium ground wholemeal (100% extraction). Bread from each was consumed by six persons for periods of 11–12 days. The daily consumption was 530–630 g. dry weight of bread and, in addition, 37 g. margarine, 284 c.c. milk, 72 g. marmalade jelly and 284 c.c. of mild ale.2. The total energy, nitrogen and fibre of the food consumed and of the faeces excreted over a period of 7 days were determined. Assuming that the foods other than bread were wholly digestible, the average percentage absorption of energy, nitrogen and fibre from the white bread was 96·1, 91·1, and 65·8 respectively; from the fine wholemeal bread it was 86·9, 85·3 and 14 respectively and from the coarser ground wholemeal 87·1, 85·7 and 9·7 respectively.3. The nitrogen intake per 100 g. of the wholemeal bread eaten, was 2·91; of the white bread 2·70 g. This advantage was, however, neutralized by the greater amount of nitrogen lost in the faeces when wholemeal was taken, so that the average net gain of nitrogen to the body was 2·46 and 2·49 respectively per 100 g. dry weight of bread consumed.4. The loss of 9% more of the energy of the bread in the faeces from wholemeal than from white bread is largely accounted for by the undigested cell envelopes and woody fibre in the bran. The greater utilization of the fibre of the white bread is in accordance with the observations of Rubner who showed that the cell membranes of the endosperm were of different composition from those of the bran cells and were more readily attacked by bacteria in the gut.5. The range of individual variations in the utilization of the energy of the breads were: for white bread 95·4–96·8% and for wholemeal 85·4–88·7%. In the utilization of nitrogen these were: for white bread 88·2–94·1%, and for wholemeal 78·5–89·6%. The same subjects showed the better utilization of both energy and nitrogen.6. The fineness of grinding of the wholemeal within the range used made no significant difference to the utilization of either energy or nitrogen.