1. Twelve young adult male volunteers were given a low-fibre white bread diet (9 g neutral-detergent fibre (NDF)/d) and a medium-fibre coarse-bran bread diet (22 g NDF/d), each lasting 20 d. In a third period of 20 d the volunteers were subdivided in groups of four, consuming a high-fibre coarse-bran bread diet (35 g NDF/d). a medium-fibre fine-bran bread diet (22 g NDF/d, bran particle size < 0.35 mm) or a wholemeal bread diet (22 g NDF/d), Retention of calcium, magnesium, iron, zinc and copper were determined during each 20 d period.
2. An increase of the amount of dietary fibre (through bran in bread) from 9 g to 22 g NDF/d resulted in a significantly increased mineral intake, but also faecal excretion increased significantly; mineral retention remained almost constant.
3. Both intake and faecal excretion of all minerals studied, except faecal Ca. increased further (P < 0.05) on the diet providing 35 g NDF/d: only Fe balance decreased significantly. No significant differences with respect to intake, excretion (except urinary Ca) and balance of the minerals could be detected between the coarse-bran bread and fine-bran bread diets providing 22 g NDF/d. Faecal Fe, Cu balance and Mg balance increased significantly during the wholemeal bread period compared to the coarse-bran bread diet providing 22 g NDF.
4. Serum cholesterol increased significantly, i.e. by 0.3 mmol/1, during the coarse-bran bread diet providing 22 g NDF, compared to the white-bread diet.
5. It is concluded that increasing the amount of bran in bread does not appear to affect mineral balance considerably but there seems to be an influence on mineral availability. The increased intake was accompanied by increased faecal excretion.