Effect of soy protein on nonheme iron absorption in man

The absorption of iron was measured from a hamburger in which half of the meat protein was substituted with various soy protein products (textured soy flour or defatted soy flour). Thge reduction of the meat content per se in the hamburgers reduced the percentage nonheme iron absorption by 25% from 11.2 to 8.4% The addition of defatted soy flour reduced the percentage absorption further from 8.4% to 5.2%. The amount of nonheme iron absorbed, however, was unchanged due to the high iron content of soy flour. A removal of phytates from soy flour did not increase the nonheme iron absorption. The total amount of iron absorbed, including the heme iron, is much lower when the content of meat was reduced by half in the soy-meat hamburgers. The addition of heme iron as blood to these hamburgers fully restored the total amount of iron absorbed to the level measured in hamburger meals prepared of meat only.