Consuming non-soy plant lignans (such as flaxseeds, sesame seeds, grains, and beans) may cut breast cancer risk, according to a new French study published in the Journal of the National Cancer Institute (2007, vol. 99, no. 6). Lignans are phytoestrogens, or estrogenlike chemicals found in plants. Their exact mechanism isn't clear, but at low doses they may act as an estrogen (which can help maintain bone density, for example). At high doses, they may actually block estrogen, which can help reduce hormone-dependent cancers such as breast, prostate, and ovarian.
Several studies have generated conflicting research about soy consumption's relationship to breast cancer. So the French researchers decided to focus on potential cancer-protective effects of phytoestrogens other than soy. They evaluated diet history questionnaires from 58,049 postmenopausal French women who weren't taking soy isoflavone supplements and did not consume a soy-rich diet.
During almost eight years of follow-up, investigators recorded 1,469 cases of breast cancer. Women with the highest lignan intake (more than 1,395 mcg per day) had a 17 percent reduced risk of breast cancer compared with those who had the lowest intake.
The protective effects were seen only with estrogen-receptor-positive (ER-positive) and progesterone-receptor-positive (PR-positive) cancers, which are stimulated by estrogen and progesterone, respectively. ER-positive cancers account for 75 percent of breast cancers; and 65 percent of ER-positive breast cancers are also PR-positive.