Should Women at High Risk for Breast Cancer Avoid Soy?

Five studies have been performed on breast cancer survival and soy foods involving more than 10,000 breast cancer patients, and together they found that those who eat more soy live longer and have a lower risk of the cancer coming back. What about women who carry breast cancer genes? Fewer than 10 percent of breast cancer cases run in families, but when they do, it tends to be mutations to one of the tumor suppressor genes, BRCA1 or BRCA2. BRCA 1 and BRCA 2 are involved in DNA repair, so if either one of them is damaged, chromosomal abnormalities can result, which can set us up for cancer.

This idea that we have tumor suppressor genes goes back to famous research from the 1960s that showed that if we fuse together a normal cell with a cancer cell, rather than the cancer cell turning the normal cell malignant, the normal cell actually suppresses the cancerous one. Tumor suppressor genes are typically split into two types: gatekeeper genes that keep cancer cells in check and caretaker genes that prevent the cell from becoming cancerous in the first place. BRCA genes appear able to do both, which is why their function is so important.

Until recently, dietary recommendations for those with mutations to BRCA genes focusedon reducing DNA damage caused by free radicals by eating lots of antioxidant-packed fruits and vegetables. If our DNA repair capacity is low, we want to be extra careful about damaging our DNA in the first place. But what if we could also boost BRCA function? In my video BRCA Breast Cancer Genes and Soy, I showed how, in vitro, soy phytoestrogens could turn back on BRCA protection suppressed by breast cancer, upregulating BRCA expression as much as 1,000 percent within 48 hours.

Does that translate out of the petri dish and into the person? Apparently so. Soy intake was associated with only a 27 percent breast cancer risk reduction in people with normal BRCA genes, but a 73 percent risk reduction in carriers of BRCA gene mutations. So, a healthy diet may be particularly important for those at high genetic risk. Meat consumption, for example, was linked to twice as much risk in those with BRCA mutations: 97 percent increased risk instead of only 41 percent increased breast cancer risk in those with normal BRCA genes. So, the same dietary advice applies to those with and without BRCA mutations, but it’s more important when there’s more risk.