Dietary Fiber Does not Significantly Reduce Mineral Absorption from Food

Other than common broscience tells you, the inclusion of healthy dietary fiber into your diet will not hinder mineral absorption. This is the result of a study by Callegaroab et al. (Callegaroab. 2010) who investigated the effect of supplementation with fiber-rich multimixtures on dietary concentration and apparent absorption of minerals in rats. Their findings are unequivocal:

The relative apparent calcium absorption was slightly decreased by the HF addition, with no change in the absolute apparent absorption. The absolute apparent absorption of phosphorus and magnesium was increased by the intermediate dietary fiber level MM [medium fiber] and HF [high fiber] additions, whereas the manganese absorption was increased only by the HF addition. The apparent absorption of copper was not affected by the MM supplementation.

With the amount of dietary calcium being (mostly) adequate, and in view of the fact that absolute absorption did not decrease, it must be concluded that increasing dietary fiber had a positive effect on overall mineral absorption, leading the scientists to conclude:

The increased apparent absorption of minerals was always related to the increase in the mineral dietary concentration triggered by the MM. Thus, we concluded that the increased dietary fiber levels in the MMs increased the mineral levels, and MMs with intermediate and high fiber levels may be used to improve the mineral balance of poor diets.