The lignans are a group of chemical compounds found in plants. Lignans are one of the major classes of phytoestrogens, which are estrogen-like chemicals and also act as antioxidants. The other classes of phytoestrogens are the isoflavones, and coumestans. Plant lignans are polyphenolic substances derived from phenylalanine via dimerization of substituted cinnamic alcohols (see cinnamic acid), known as monolignols, to a dibenzylbutane skeleton 2. This reaction is catalysed by oxidative enzymes and is often controlled by dirigent proteins.
Many natural products, known as phenylpropanoids, are built up of C6C3 units (a propylbenzene skeleton 1) derived from cinnamyl units just as terpene chemistry builds on isoprene units. Structure 3 is a neolignan.
When part of the human diet, lignans are converted into the mammalian lignans known as enterodiol (1) and enterolactone (2) by intestinal bacteria.
Flax seed is among the highest known sources of lignan. The principal lignan precursor found in flaxseed is secoisolariciresinol diglucoside. Other sources of lignans include pumpkin seeds, sesame seeds, rye, soybeans, broccoli, beans, and some berries.
Secoisolariciresinol and matairesinol were the first plant lignans identified in foods. Pinoresinol and laricresinol are more recently identified plant lignans contribute substantially to total dietary lignan intakes. Typically, Lariciresinol and pinoresinol contribute about 75% to the total lignan intake while secoisolariciresinol and matairesinol contribute only about 25%.
Sources of lignans:
|source||Amount per 100 g|
|sesame seed||29 mg|
|Brassica vegetables||185 - 2321 µg|
|Red wine||91 µg|
- Milder IE, Arts IC, van de Putte B, Venema DP, Hollman PC (2005). "Lignan contents of Dutch plant foods: a database including lariciresinol, pinoresinol, secoisolariciresinol and matairesinol". Br. J. Nutr. 93 (3): 393–402. PMID 15877880.