Legumes and Mineral Absorption, With Special Reference to Soybean Proteins

Abstract

Among the legume foods, soy proteins are finding increased use in human diets. Hence, selected aspects of dietary mineral absorption and availability in reference to soy proteins are reviewed, with particular attention being given to the human nutritional context. Data from animal feeding studies are considered first as a basis for indicating the value, as well as limitations, of data from animal bioassays on mineral absorption as they may relate directly to human feeding. It is apparent that the availability of zinc and iron in soy-based diets given to animals is variable and it is difficult to draw generalized conclusions about legumes and mineral absorption in reference to man. The limited data obtained in human metabolic studies are reviewed and they lead to the conclusion that well-processed soy concentrates and isolates do not impair zinc absorption or nutriture. The effects of diets based on significant intakes of soy foods on the absorption of iron are still unclear although the major available evidence does not suggest significant untoward consequences of increased soy-protein intake on body iron nutriture. This problem deserves more attention, and not only with respect to iron but also other trace elements for which data in human subjects are limited or entirely lacking. Preliminary results of studies of MIT experiments, in which stable isotope probes are being developed to quantify mineral bioavailability, arc reviewed as a basis for indicating possible novel and useful approaches for exploring quantitative aspects of nutrient bioavailability in diets consumed directly by man.