Factors influencing the absorption of iron from soya-bean protein products

1. The absorption of iron from soya-bean (Glycine hispida)-based and milk-based infant formulas was assessed in 138 multiparous Indian women, using the erythrocyte utilization of radioactive Fe method. 2. Fe absorption was significantly greater from the basal milk formula (1.5 g protein) than it was from the basal soya-bean formula (2.3 g protein), with geometric mean values of 0.083 and 0.044 respectively. 3. Ascorbic acid markedly increased Fe absorption from the milk-based formula in a dose-dependent fashion. The increase was fivefold when the ascorbic acid: Fe ratio on a weight-for-weight basis was 6:1 and over tenfold when it was 20:1. In contrast, ascorbic acid had a less-marked effect on the absorption of Fe from the soya-bean-based formula, with only a two-to threefold increase at an ascorbic acid:Fe ratio of 20:1. 4. The geometric mean Fe absorption from the soya-bean formula (1.27 mg Fe, 2.3 g isolated soya-bean protein (ISP)) was somewhat less than that from the same amounts of ISP and ascorbic acid made up in milk (0.075 and 0.113 respectively). However, a direct comparison between the soya-bean formula in milk and in water showed no significant difference (0.043 and 0.060 respectively). 5. Fe absorption from a drink containing 10 g ISP and 30 mg ascorbic acid was significantly better than that from a similar drink containing the soya-bean flour from which ISP is extracted (0.044 and 0.027 respectively). 6. Heating ISP to 200° for 2 h before its use had no effect on Fe availability. When 2.3 g heated ISP (10 mg ascorbic acid) was compared with a similar formulation of untreated ISP, Fe absorption values were 0.135 and 0.099 respectively. Comparable values with 25 g ISP (no ascorbic acid) were 0.067 and 0.058. 7. Citric acid in amounts of 1-4 g had a dose related but limited enhancing effect on Fe absorption from 10 g ISP, with a rise from 0–011 (no citric acid) to 0.068 (4 g citric acid). 8. There was appreciable variability in the levels of Fe absorption in different studies, which suggested that unidentified manufacturing or preparative differences might be influencing the overall results. © 1987, The Nutrition Society. All rights reserved.