Some months ago I decided to start incorporating soy products in my cooking and did a lot of reading on the subject. What I found was that soy flour by itself will not make good bread, but it should be mixed with your regular flour. The proportions are 1 part soy flour to 3 parts regular. You can, of course, experiment to find your own preference.

I have used soy flour in a couple of different bread recipes and can tell a slight difference in the flavor and texture. It's good, but a little denser than my usual finished product.