Lignans are a diverse class of secondary plant metabolites formed by the dimerization of two phenylpropanoid units linked by a beta-beta' carbon bond. They occur widely in seeds, grains, fruits, and vegetables, with notable dietary sources including flaxseeds, sesame seeds, and whole grains. Lignans exhibit phytoestrogenic, antioxidant, and anti-inflammatory properties. Upon ingestion, many are metabolized by gut microbiota into enterolignans such as enterodiol and enterolactone, which may influence hormone metabolism and have been studied for potential roles in reducing risks of certain cancers and cardiovascular diseases. Structural variations include secoisolariciresinol, matairesinol, pinoresinol, and lariciresinol. They are lipophilic and contribute to the health benefits associated with high-fiber plant foods.