The Whole Soy Story.
What most people do not realize, however, is that due to the predominance of soy in animal feeds, soy protein is probably present in your food even if it is not listed as an ingredient anywhere. Very little testing has been done to determine if the soy protein from the animal feed is passed into the end products we consume. Most laboratories do not even have tests available to test for this.
Professor M. Monica Giusti, a poultry biologist of The Ohio State University, is one of the few people who has done research on soy isoflavones appearing in commercial egg yolks. She has designed lab tests to detect soy isoflavones. In 2009 one of her students published a master’s thesis on the transfer of the soy protein into egg yolks and chicken tissue: Quantification of Soy Isoflavones in Commercial Eggs and Their Transfer from Poultry Feed into Eggs and Tissues."
Article in its entirety: http://healthimpactnews.com/2011/soy-protein-present-in-all-egg-yolks-and-chicken-tissues/