Soy is a great source of plant-based protein, but many people are wary of how consuming soy products could affect their body’s hormones, including estrogen, or how it may interact with other substances, such as medications. 

A new study from Georgetown University Medical Center examined the potential positive and negative effects of soy consumption on a common breast cancer treatment. Researchers highlighted one component of soy, called genistein, and its effect on breast cancer - especially for those being treated already with the drug tamoxifen.

According to a press release from Georgetown University, the research team looked at advanced models of rat breast cancer. They found that the effectiveness of tamoxifen was actually improved and recurrence of breast cancer was less likely with soy consumption.

Read: Soy intake associated with lower recurrence of breast cancer in hormone-sensitive cancers

Additionally, study results showed that longtime sustained use of genistein prior to the development of breast cancer improves overall immunity against cancer. Sounds good, right?

Well, results of the study also showed that eating or drinking soy-based foods for the first time while being treated with tamoxifen can actually reduce effectiveness of the drug, and promote recurrence of breast cancer.

Read: A high-soy diet may drive breast tumor growth: study

“There has long been a paradox concerning genistein, which has the similar structure as estrogen and activates both human estrogen receptors to a degree. Estrogen drives most breast cancer growth, yet high soy intake among women in Asian countries has been linked to a breast cancer rate that is five times lower than Western women, who eat much less soy,” explained the study’s senior investigator, Leena Hilakivi-Clarke, PhD, according to the press release.

Source: Zhang X, Cook KL, Warri A, Cruz IM, Rosim M, et al. Lifetime Genistein Intake Increases the Response of Mammary Tumors to Tamoxifen in Rats. Clinical Cancer Research. 2017.

Read Also:

Soy Protein Might Exacerbate Breast Cancer In Women Who Already Have The Disease

Eating Soy in Adulthood May Increase Breast Cancer Treatment Resistance