Apparent absorption and retention of Ca, Cu, Mg, Mn, and Zn from a diet containing bran

To establish conditions for comparisons of mineral bioavailability from plant sources, seven male subjects consumed a constant diet containing bran fiber and phytate. Absorption and retention of Ca, Cu, Mg, Mn, and Zn were measured for 7-day periods through wk 2-7. Intakes of Mg, Mn, and Zn significantly exceeded the RDA; Ca and Cu intakes were only slightly in excess of RDA. All mineral retentions fluctuated from week to week but only Mg and Mn showed a consistent positive trend over time. Phytate excretions showed characteristic individual patterns, but did not appear to change with time. In contrast to previous observations fecal recovery of polyethyleneglycol (PEG) (MW = 4000) was consistently lower than recovery of simultaneously ingested Cr. Only five of the seven subjects returned close to 100% of Cr within 7 days. It was concluded that at least 4 wk were needed for adaptation in investigations involving more than one mineral when the experimental diet is adequate in the nutrients under investigation, that measurements of responses to treatment required 2-3 wk each, and that successive isotopically labeled test meals may overlap if they are spaced at 7-day intervals.