-Furthermore, modern soy foods are very different from those consumed traditionally in Asia. Most are made with soy protein isolate (SPI), which is a protein-rich powder extracted by an industrial process from the waste product of soy oil manufacturing. It is the industry's way of making a profit on a waste product. The industry spent over 30 years and billions of dollars developing SPI.
In feeding studies, SPI caused many deficiencies in rats. That soy causes deficiencies in B12 and zinc is widely recognized, but the range of deficiencies was surprising.