Soy protein supplements accelerated the growth of tumors in women with breast cancer, according to a study conducted by Memorial Sloane Kettering Cancer Center in New York.
Some women increase their intake of soy protein supplements in hopes that it will prevent breast cancer, but studies haven’t been able to prove that there was a benefit to consuming soy, only that there was an association between soy intake and a decreased breast cancer risk.
This new study, published in the Journal of the National Cancer Institute, looked at the effects of soy protein on women already diagnosed with breast cancer, reports Reuters. Soy protein containsphytoestrogens, which mimic estrogen behaviors. The researchers looked at the molecular structure of early breast cancer cells taken during biopsies. They compared those again with the tumor, once it had been removed. The study participants were taking either a soy or milk protein supplement during the time between the collection of samples.
“Compared to tumors in the milk group, the tumors in the soy group were ‘overexpressing’ genes associated with the cell cycle and cell proliferation,” Reuters explained. “For some in the soy group, expression of a gene associated with cancer growth increased, too,” the authors noted.
While the authors aren’t clear on what’s causing the response to the soy protein, the findings draw a clear connection to soy’s ability to impact the tumors. “All we can say is that in some of the women, the soy component drove proliferative genes, at the gene level,” said lead author Dr. Moshe Shike . “How it would translate into cancer outcome we can’t say.”
“What we recommend is moderation, meaning we think that taking excessive amounts of soy may not be a good idea,” Shike said. “We don’t have clinical proof for that because this is only gene expression.”