Many women with estrogen receptor positive (ER+) breast cancer have concerns about eating any foods rich in phytoestrogens. Since flaxseed is the richest dietary source of lignans which are a type of phytoestrogen, concerns have been raised about whether women with ER+ breast cancer should avoid them.
Phytoestrogens are plant nutrients that have some similarity to the natural female hormone, estrogen. Lignans therefore may have pro-estrogenic and/ or anti-estrogenic effects in the body. They are thus at the centre of the debate as to whether or not it is safe for women with breast cancer to eat flaxseeds.
Phytoestrogens are found in many foods, including soy, flaxseeds, whole grains, other nuts and seeds and some vegetables and fruits. Most of the research on flaxseed and breast cancer has focused on the lignans in flaxseed and their potential for weak estrogenic or anti-estrogenic effects in a woman’s body.
Since phytoestrogens are somewhat similar to human estrogen, some health experts have hypothesized that they may act like human estrogen in the body. This has therefore raised concerns about their safety for people with hormone linked cancers such as prostate cancer, endometrial cancer or ER+ breast cancer.
Lignans certainly can change estrogen metabolism. In postmenopausal women, they can actually cause the body to produce less active forms of estrogen. This potentially reduces breast cancer risk. There is also evidence that adding ground flaxseeds to ones diet decreases cell growth in breast tissue, the type of change that would likely decrease breast cancer risk.
All cells are able to undergo a process of programmed cell death, or apoptosis. Through this mechanism, the body prevents damaged cells from reproducing and eventually developing into cancerous cells. Researchers have shown that flaxseed sprouts can increase apoptosis and some studies have found that two specific phytoestrogens found in lignans, may help suppress breast tumour growth.
Some animal studies have shown that both flaxseed oil and lignans can reduce breast tumour growth and spread, even in estrogen receptor negative breast cancer. This suggests that flaxseeds may have anti-cancer benefits that are unrelated to any effect on estrogen or estrogen metabolism.
Tamoxifen is a breast cancer drug with which many people reading this column may be familiar. It is a selective estrogen receptor modulator, or SERM. It is often prescribed as part of the treatment for women with ER+ breast cancer. It binds with estrogen receptors thus preventing the woman’s own estrogen from binding with these receptors. This effectively blocks the growth of breast cancer cells that are driven by estrogen.
Adding flaxseeds to the diet seems to have promise for women with breast cancer. In women who have already been eating flaxseeds prior to their diagnosis, their tumours are often less aggressive. As with all my recommendations, intake should be through diet only, and not by supplementation. Only moderate amounts of ground flaxseeds should be eaten daily. Do not have more than two to three tablespoons per day. Remember there is no such thing as one cancer-defeating wonder food!