Metabolism in rats of selenium from intrinsically and extrinsically labeled isolated soy protein.

Absorption, retention and tissue accumulation by rats of 75Se from intrinsically labeled isolated soy protein were compared with utilization of 75Se from the extrinsic sources of [75Se]selenite, [75Se]selenate or [75Se]selenomethionine. Extrinsic sources of selenium were given by gavage or mixed with isolated soy protein. There were no differences in absorption and retention of 75Se from intrinsically labeled soy diet compared to the three extrinsically labeled soy diets. Of the three extrinsic sources tested, 75Se from selenate was better absorbed than from selenite or selenomethionine when incorporated into a soy diet. Absorption of 75Se was significantly lower when given to animals in gavage solution than when mixed with soy diets. After a 14-d test period, retention of 75Se was the same for all four soy diet groups. In gavaged groups, 75Se from selenomethionine was retained to a greater extent than 75Se from selenite. The liver, testes and kidney accumulated more 75Se from the test meal than did the blood and lungs. In the testes more 75Se from selenite and selenate was accumulated than from selenomethionine-labeled diets. Selenium absorption from the soy isolate source was very high (86-96%), indicating that, although soy does not normally contain high levels of selenium, the selenium present is well absorbed from this plant source.