The lignans are a large group of polyphenols found in plants. Some examples of lignans include enterolignans, enterodiol and enterolactone. Lignans are one of the major classes of phytoestrogens and a part of the human diet. Plant lignans such as pinoresinol, lariciresinol, secoisolariciresinol, matairesinol, hydroxymatairesinol, syringaresinol and sesamin can be metabolized by intestinal bacteria into mammalian lignans enterodiol and enterolactone, which are playing a role in cancer-protective effect of vegetarian diets. Lignans have an antioxidant role in the plant defence against biotic and abiotic factors, and are under basic research for their potential anti-inflammatory or antioxidant activities in laboratory models of human diseases.