If you have taken a look through the internet, you will see that it is very difficult to find any concrete research to support the idea that herbs, or phytoestrogens can specifically change the size and shape of breasts. The reason this is so, is in the name of monetary reasons.
Many of the studies that have been done to investigate the effects of herbs on breast development past puberty are done by companies that have a financial interest. That is, they have a product, and they want to test the results of their product, NOT the herbs within. Thus, the company will conduct scientific studies on the NAME of the product, not the actual ingredients.
If you know of any great studies, please comment them below for others to see!