The effects of breads containing similar amounts of phytate but different amounts of wheat bran on calcium, zinc and iron balance in man.

The capacity of wheat bran to impair mineral absorption independent of its phytate content was studied by metabolic balance studies in man. Three breads were prepared, equivalent to white, brown and wholemeal, by adding bran in different quantities to white flour. Calcium, iron, zinc and sodium phytate were added to the loaves to make the amounts equal in all breads. Six healthy volunteers were studied for three consecutive 24-d-periods during which they ate a controlled diet, typical of that normally consumed in the UK but with 200 g bread/d. Only the type of bread changed between each dietary period. The phytate contents (mmol) of 200 g of each of the breads after baking were: white 2.3, brown 2.1 and wholemeal 2.2; non-starch polysaccharide contents (g) were: white 3.3, brown 10.9 and wholemeal 18.7. The increased amount of bran in the breads increased stool output in the expected way but no change was seen in Ca, Zn and Fe balance. Blood levels of these minerals remained unchanged. It is concluded that wheat bran and, in particular, the cell-wall polysaccharides of bran, are unlikely to exert a significant effect on mineral absorption in man, in amounts customarily eaten, independently of the effect of phytate present in the bran.