Bioavailability of Iron from Western-Type Whole Meals

Abstract

The absorption of non-heme iron was measured in 10 meals designed to correspond to a whole main meal with an energy content of about 1000 kcal. The extrinsic tag method was used to label the non-heme iron, and two meals were compared in each subject by means of two radioiron isotopes. All absorption figures were related to the absorption of a 3-mg reference dose of inorganic iron, and all absorption figures were normalized to a 40% absorption from the reference dose, a level corresponding to absorption in subjects who are borderline iron-deficient. In spite of the similar energy content of the meals and only a twofold variation in content of non-heme iron (3.9-7.8 mg), there was a fivefold difference in absorption of non-heme iron (0.33-1.80 mg). Considering also the content of heme iron in the meals, the calculated variation in absorption was sixfold (0.33-1.95 mg). The main part of this variation can be explained by a varying content of ascorbic acid and meat. The absorption of iron from meals can be expressed in different ways. The percentage absorption is a measure of the bioavailability, which can be markedly modified by several components of a meal. The amount absorbed is, moreover, related to the amounts of heme and non-heme iron present. The amount absorbed per unit energy in the meal, the bioavailable nutrient density, is an expression of great importance in the practical assessment of the nutritive value of a meal with respect to iron.