¡¡¡¡ Lignans are natural compounds with two or three molecules of benzene propyl¡äs combination by various modalities. Being phytoestrogen, flax lignans can weakly bind to estrogen receptors(ER) and interfere hormone metabolism as soya isoflavones. The main ingredient of flax lignans is secoisolariciresinol diglucoside(SDG), SDG is the precursor of mammal lignans because it is converted into enterolactone(EL) and enterodiol(ED) following ingestion. Dietary flaxseed obviously increases plasma EL and ED concertrations up to 200 and 48 times, respectively.Researches have shown that urinary excretion of lignan metabolites was a dose-dependent biomarker for flaxseed intake with the doses consumed. Continuous administration of SDG did not cause its excretion delayed, an evidence of safety for using dietary SDG supplement. Most part of urinary lignans are their monoglucuronides.The metabolism and mechanism is as follows