Breast cancer occurs when cells within the breast begin growing in a rapid and unregulated way. These cells may still respond to hormones, so part of treating these types of cancers requires doctors to monitor hormone levels. Some foods, including soy, have compounds that can interfere with hormone levels, though it is unclear if soy is good or bad for breast cancer.
Soy Components
Soy protein contains many chemicals. For example, soy contains proteins known as protein kinase inhibitors, which can help regulate cell growth and also contain saponins and phytosterols that can help keep cholesterol levels low. Soy also contains important antioxidants that can help prevent DNA damage. Of particular relevance to the field of breast cancer are isoflavones, a type of chemical found in all soy products. These chemicals are similar in structure to estrogen, BreastCancer.org says.
Phytoestrogens and Breast Cancer
One of the concerns about isoflavones is that some breast cancer cells divide more quickly in the presence of estrogen. A 2008 article in "Nutrition Journal" reviews some of the research that has been done on soy products and cancer risk. Although the isoflavones found in soy can stimulate the growth of breast cancer cells in laboratory animals and cell cultures, these findings have not been found in humans, which means that it is not clear whether soy isoflavones can be bad for breast cancer patients.
Soy and Cancer Prevention
Some researchers suggest that increasing your soy intake can help lower your risk of developing breast cancer, the American Cancer Society says. Women who consume more soy products may be less likely to get breast cancer, but these studies need to be done carefully to account for other factors. The timing of soy intake is also important. According to the Harvard School of Public Health, eating more soy during adolescence and early adulthood can help lower your breast cancer risk.
Recommendations
Because researchers are still investigating the effects of soy on breast cancer, you may want to avoid soy-based supplements with isoflavones if you have breast cancer, BreastCancer.org says. You can, however, eat soy as part of your diet. One to three servings of soy each day is most likely safe. If you are taking medications that affect your hormone levels as a treatment for breast cancer, talk to your doctor about whether soy is safe for you.
