1. Iron and zinc retentions in young male rats, given 3 g starch–sucrose paste containing 120 μg Fe as FeSO4 or 139 μg Zn as ZnC12 (extrinsically labelled with 59Fe or 65Zn) and increasing amounts of Gypsophila saponins, were measured by whole-body counting. The results were compared with whole-body Fe and Zn retention from a meal containing crude or purified saponin fractions. In a separate experiment Fe retention from a meal containing Gypsophila saponins, soyasaponin I, or saponins extracted from lucerne (Medicago sativa) plant tops, was measured in older rats.
2. Results indicated that Fe absorption decreased with increasing concentration of Gypsophila saponins. This was significant at a saponin: Fe molar value of approximately 1, with maximum effect occurring at molar ratios of 4 and above, when Fe absorption was reduced by approximately 17%. Gypsophila saponins had no effect on Zn absorption from a test meal.
3. Fe absorption was similar in groups given purified or crude Gypsophila saponins at the same saponin: mineral molar value of 8, demonstrating that the ‘non-saponin’ fraction of the commercial preparation does not affect the absorption of this mineral.
4. Saponins extracted from lucerne plant tops, fed at a saponin:Fe value of approximately 8, also reduced Fe absorption from a single meal. Fe absorption from a meal containing a similar amount of soyasaponin I was not significantly different from controls.
5. These results indicate that some dietary saponins may reduce Fe absorption and hence have an adverse effect on Fe status in man and simple-stomached animals.