IRON BIOAVAILABILITY STUDIES AS ASSESSED BY INTRINSIC AND EXTRINSIC LABELING TECHNIQUES (BIOAVAILABILITY, HEMOGLOBIN, SOY)

CATHERINE DUBININ JOHNSON, Purdue University

Abstract

Although soybeans are a rich source of iron and incorporation of soy protein into diets is increasing, the presence of phytate or fiber endogenous to the seeds may inhibit total iron absorption from diets including soy protein. Four studies on iron bioavailability as assessed by intrinsic and extrinsic labeling techniques in rats were completed. The effect of previous dietary protein on the absorption of intrinsically ('59)Fe labeled defatted soy flour was determined in rats. The results indicated that the type of dietary protein (animal vs. plant) in pre-test diets would have little influence on iron absorption from a single soy protein test meal. Therefore, adaptation of soy protein does not improve bioavailability of iron. Soybean hulls are a concentrated source of iron and are a cheap byproduct of soybean processing. Therefore, they were investigated as a source of iron fortification in bread. The results indicated that retention of ('59)Fe from white bread baked with soy hulls did not differ from white bread fortified with bakery grade ferrous sulfate. Limitations for use of the extrinsic label were also investigated. Percent retention of ('59)Fe was dependent on the method of extrinsic labeling. Extrinsic labeling was found not to be an appropriate method for monitoring iron absorption from large particle size iron. The effect of endogenous soybean phytate on iron absorption in rats was measured using seeds of varying phytate content and intrinsically labeled with ('59)Fe. Increasing concentration of phytate in whole soybean flour had no significant effect on iron absorption. The hemoglobin regeneration bioassay and absorption of a radioiron test meal for assessing iron bioavailability were compared. A protocol for the radioiron assay that produced the highest correlation with the hemoglobin regeneration bioassay (r = 0.976) resulted when rats were depleted in iron (4.5 g hgb/dl) and received a 25 ppm iron test meal intrinsically or extrinsically labeled with ('59)Fe with no prior adaptation to the iron source.

Degree

Ph.D.

Subject Area

Nutrition

COinS