British Journal of Nutrition

Papers of direct relevance to Clinical and Human Nutrition

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

D. P. Dermana1, D. Ballota1, T. H. Bothwella1*, B. J. Macfarlanea1, R. D. Baynesa1, A. P. Macphaila1, M. Gilloolya1, J. E. Bothwella1, W. R. Bezwodaa1 and F. Mayeta2

a1 Joint UniversitylSouth African MRC Iron and Red Cell Metabolism Unit, Department of Medicine, University of the Witwatersrand Medical School, 7 York Road, Parktown, Johannesburg 2193, South Africa

a2 Department of Medicine, University of Natal Medical School, Congella, Durban, South Africa

Abstract

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 0.1 13 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 0.01 1 (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.

(Received August 19 1986)

(Accepted January 09 1987)

Footnotes

* For reprints.