Lignans are a group of polyphenolic compounds found in plants, especially flaxseed, sesame seeds, and whole grains. They are phytoestrogens, meaning they have a structure similar to estrogen and can exert weak estrogen-like effects in the body. Scientific interest in lignans for breast health arises from epidemiological and laboratory studies suggesting that higher intakes of lignan-rich foods may be associated with a reduced risk of breast cancer, particularly in postmenopausal women. The proposed mechanisms include modulation of estrogen metabolism, antioxidant activity, and the potential inhibition of tumor growth.

Several observational studies have linked higher dietary intake or higher blood/urinary levels of lignans with a lower risk of breast cancer. Some clinical trials have shown that flaxseed supplementation, which is high in the lignan secoisolariciresinol diglucoside (SDG), can favorably alter estrogen metabolism and reduce tumor cell proliferation markers in breast tissue. However, results are not universally consistent, and few randomized controlled trials have tested lignan effects specifically on breast health endpoints in humans.

While there is a plausible biological rationale and some supportive human data, the overall evidence is moderate. Lignans are not a guaranteed or primary intervention for breast health, but their inclusion in the diet (mainly from flaxseed) is reasonably supported by current scientific literature for potential benefit, especially as part of a healthy dietary pattern.