What Is the Effect of Phytoestrogen on Breasts

Phytoestrogens are plant hormones chemically similar to the estrogens found in humans. An example of a phytoestrogen is soy. Phytoestrogens treat a variety of health conditions and affect breast tissue. There are claims that phytoestrogens may enhance breast development, but a greater volume of research has investigated how phytoestrogens effect breast cancer. Epidemiological studies primarily show phytoestrogens to have a protective effect against breast cancer.


Phytoestrogens are plant estrogens that attach to estrogen receptors in humans, effecting hormones in the body. When they bind to estrogen receptors, they may either promote or inhibit estrogen, but the behavior depends on the amount of circulating estrogens and the number and type of estrogen receptors.

Phytoestrogens help to reduce cholesterol and blood pressure, menopause symptoms, the risk of certain cancers and the risk of osteoporosis.

Classes of phytoestrogens include isoflavones, lignans and coumestans. Isoflavones, specifically genistein and daidzein, have the highest estrogen properties and are found in legumes such as soy, chickpeas, clover, lentils and beans. Lignans are found in flaxseeds, lentils, whole grains, beans, berries, fruits and vegetables. Coumestans are found in sprouting plants. Phytoestrogens, primarily isoflavones, are also found in processed and packaged foods and in infant soy formula. Often they are used as a preservative.

Effect on Breast Tissue

Because phytoestrogens mimic estrogen, interest exists on how they effect the body's hormones. How phytoestrogens effect breast tissue is an area of much speculation, specifically in areas such as breast cancer and breast enlargement. Phytoestrogens have the biggest impact on breast tissue when exposure occurs prior to puberty. There is an association between high soy intake early in life and increased breast density.

Effects of Phytoestrogens on Breast Development

Claims exist that phytoestrogens may increase breast size. A March 2010 study published in the “BOR Papers in Press” stated that genistein exposure in infants fed soy formula induces estrogenic changes in both reproductive and non-reproductive organs. Another study in the “Journal of Pediatric Gastroenterology and Nutrition” in February 2008 showed that infants fed soy formula had an increase in breast development in the second year of life, suggesting that phytoestrogens contribute to the retention of infantile breast tissue. These studies reflect infantile exposure to soy in extremely high amounts, not consumers seeking to increase breast size. Many cosmetic and supplement companies advertise their products to increase breast size due to phytoestrogens, but use caution before you purchase these products.

Phytoestrogen Effects on Breast Cancer

Overall, phytoestrogens have a protective effect against breast cancer, though research has shown that in some cases they may induce tumor development. A study in the "Journal of Clinical Oncology" in February 2007 showed phytoestrogens to behave like estrogen when natural estrogen levels are low and unlike estrogen when levels are high. Premenopause, phytoestrogens protect against breast cancer when estrogen levels are high, but promote the growth of cancer cells post-menopause when estrogen levels are low. This study also showed that higher levels of the isoflavone genistein slows the development of tumor cells, protecting against breast cancer.