In addition, when SD or flaxseed were added to the diet of pregnant and lactating rats, reproductive birth defects were found in the newborn rats. Until more is known, it is a good idea for pregnant and nursing mothers to limit the amounts of flaxseed they eat on a regular basis. The lignans are thought to act as either antioxidants or as phytoestrogens. As antioxidants these chemicals can inactivate free radicals, very reactive chemicals which can damage cells. Acting as phytoestrogens, the mammalian lignans may change the metabolism of estrogens or increase the level of a protein that binds estrogens in the blood.
Grains also contain a sugar-like chemical known as phytic acid.
This chemical has been shown to reduce the number of mammary tumors in rats. How phytic acid works is unclear but it may act through changes in liver metabolism, as an antioxidant, as an agent to eliminate harmful metals, or by action on the communication between cells. Grains, fruits and vegetables are all good sources of chemically complex molecules, known as flavonoids. Flavonoids from grains have been studied very little. Nonetheless, flavonoids from other plants limit the growth of breast tumor cells, and a large cohort study found a decrease in all types of cancer with higher levels of flavonoids in the diet.