Determination of iron absorption by rat bioassay. Evaluation of methods of dosing 59Fe on radioiron absorption from plant diets.

We studied the potential of an animal model to predict nonheme iron absorption in humans and tested a feasible and easy technique of dosing 59Fe to evaluate bioavailability of dietary nonheme iron. Plant diets containing about 20 ppm or 75 ppm iron were the nonheme iron sources with ferrous sulfate (75 ppm) as a reference. Radioiron was administered by (a) gavaging in water, 1 h after a meal; (b) mixing with the meal; and (c) making a slurry with the meal and gavaging. No significant differences were found (P less than or equal to 0.05) in 59Fe absorption among the three methods of administering radioiron. Absorption of 59Fe was similar to apparent iron absorption for all diets tested, whether the animals consumed the same diet as that of the test meal or a different diet. A high correlation (r = 0.88) obtained between the apparent iron absorption and 59Fe iron absorption for different dosing techniques, indicates that extrinsic iron tag administered by any of these methods is valid to measure nonheme iron absorption. Apparent iron absorption values determined by rats fed 20 ppm or 75 ppm dietary iron from plant sources were similar to reported values for humans. It is concluded that the normal adult rat is an appropriate model to study iron bioavailability of human foods when iron status, maturity, iron intake relative to requirement, and method of measurement are similar to the human situation.