Flax lignans, particularly secoisolariciresinol diglucoside (SDG), have been studied for their potential role in supporting breast health, including benign breast lumps (such as fibrocystic breast changes). Lignans are phytoestrogens—plant-derived compounds with weak estrogenic activity. There is scientific interest because they may exert anti-estrogenic effects in breast tissue by modulating estrogen metabolism and binding to estrogen receptors, potentially reducing the risk of abnormal cell proliferation.

Some clinical and preclinical studies suggest that diets rich in flaxseed (the main source of flax lignans) can alter estrogen metabolism and may be associated with a reduced risk of breast cancer and possibly benign breast conditions. For example, small trials have shown that flaxseed supplementation can decrease cell proliferation in breast tissue of premenopausal women and may reduce breast pain and nodularity in women with benign breast disease. However, these studies are generally small, of short duration, and sometimes lack rigorous controls.

While there is a plausible mechanism and early clinical evidence, the overall quality and quantity of data are limited. Major health organizations do not currently endorse flax lignans as a treatment for breast lumps. Thus, the evidence supporting flax lignans for this use rates as modest (2/5)—promising but far from conclusive, and more research is needed.