IRON-ABSORPTION BY RATS FED TANNINS EXTRACTED FROM BEAN HULLS

Nutritional balance and whole-body radioassay procedures were used to assess the effects of tannins extracted from hulls of beans (Phaseolus vulgaris) on iron (Fe) absorption by male rats fed test meals labeled extrinsically with Fe-59. Tannin in single meals did not affect Fe-59 absorption by moderately anemic, growing rats when Fe-59 was added di rectly to the whole meal or when it was added to casein before it was incorporated into the meal. However, addition of Fe-59 to either bean tannin or to tannic acid prior to including it in the meal depressed F e-59 absorption compared to that from tannin-free meals. In growing, a nemic rats fed diets with 0, .06, .125, .25 or.5% tannin before and af ter test meals, Fe-59 absorption averaged about 82, 81, 72, 72 and 71% of the dose, respectively; absorption of Fe-59 by rats fed diets with either 0 or .06% tannin was greater than that of rats fed the other d iets. These data suggest a threshold effect of tannins on inhibition o f Fe absorption. Similarly, compared to rats fed a tannin-free diet, F e-59 absorption was depressed in growing, Fe-adequate rats fed a diet with .5% tannin. In contrast, tannins did not affect Fe-59 absorption by mature rats. Although some impairment in Fe absorption in growing r ats resulted from consumption of tannin-containing diets for several d ays, bean tannins consumed as part of typical diets probably have litt le adverse effect on Fe absorption.