lignaner

Lignans are a diverse group of plant-derived polyphenolic compounds formed by the oxidative coupling of two cinnamyl alcohol units. They are typically dimers or tetramers and are distinct from the lignin polymers that strengthen plant cell walls. In humans, the most studied dietary lignan is secoisolariciresinol diglucoside (SDG), found in flaxseed, which can be metabolized by gut microbiota into enterodiol and enterolactone.

Natural sources of lignans include flaxseed as the richest source, with significant amounts also present in sesame seeds, whole grains, legumes, fruits, and vegetables. The levels and specific lignans vary by plant species and cultivar. In plants, lignans are produced via the phenylpropanoid pathway, and their biosynthesis involves enzymes and dirigent proteins that guide stereoselective coupling of monolignol units to form the lignan skeleton.

In humans, gut bacteria convert plant lignans into enterolignans, mainly enterodiol and enterolactone. These metabolites can interact with estrogen receptors and are regarded as phytoestrogens, typically displaying weak estrogenic or antiestrogenic activity depending on tissue context. Lignans also exhibit antioxidant and anti-inflammatory properties in laboratory studies, though the significance of these effects in humans remains under investigation.

Health effects and research are inconclusive at present. Some observational and clinical studies have explored possible associations between dietary lignans and reduced risk of hormone-related cancers or cardiovascular disease, but evidence is not definitive. Lignan intake through diet is generally considered safe, while high-dose supplements are not approved as medical treatments and should be used with caution in hormone-sensitive conditions.