For years, there’s been confusing debate over whether breast cancer survivors should eat soy. However, a new study presented at the American Association for Cancer Research (AACR) found that women who ate the most soy food didn’t increase their risk of breast cancer recurrence, but reduced their risk.
Since soy foods contain large amounts of isoflavones, survivors had been advised against consuming them. Isoflavones are phytochemicals (chemicals found in plants) that have both estrogen-like and anti-estrogenic effects.
Estrogen (a female sex hormone) has been linked to cancer growth, especially breast cancer, whereby breast cancer patients are often treated with a chemotherapy drug that blocks estrogen (tamoxifen). Scientists theorized that isoflavones can compromise the effect of tamoxifen since both tamoxifen and isoflavones bind to estrogen receptors*.
The researchers studied the diets of over 9,515 breast cancer patients from the U.S. and Shanghai. The study assessed the diets of these women 14.6 months after their cancer diagnosis and followed them for 7.4 years. They looked at how often they ate soy foods like:
- Soy milk
- Cooked soybeans
- Miso soup
- Soybean sprouts
- Protein shakes with added soy
The most frequently consumed soy foods were tofu and soy milk. The average daily intake for U.S. women was 3.2 mg. and 45.9 mg. for Shanghai women.
The women who ate the most soy food (at least 11.83 mg. of isoflavones per day) had a 27% reduced risk for breast cancer recurrence compared to those with the lowest intake (3.68 mg or less per day).
Researchers concluded consuming a cup of soy milk or two ounces of tofu per day would provide the levels of isoflavones needed to get the beneficial effects. They warned that soy supplements, though, are not recommended for reducing the risks of breast cancer because the amount and type of isoflavones in them may differ from actual soy foods.
*An estrogen receptor is a protein molecule that’s embedded within a cell. Before the body can use estrogen, it must bind to an estrogen receptor. Picture this…Your body produces estrogen (or perhaps you get it through hormone replacement drugs) and the estrogen approaches a door, i.e., the “cell”. The estrogen receptor is the “lock” on the door, and the estrogen is the “key” which unlocks the door and allows estrogen to function inside your body.