What are Lignans and where can I find them?

The lignans are a group of chemical compounds found in plants. Plant lignans are polyphenolic substances derived from phenylalaninevia 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. 

Plant lignans are co-passengers of dietary fiber, and therefore fiber-rich food items are often good sources of lignans. Flax seed andsesame seed contain higher levels of lignans than most other foods. The principal lignan precursor found in flaxseed issecoisolariciresinol diglucoside. Other sources of lignans include cereals (rye, wheat, oat and barley - rye being the richest source),soybeans, cruciferous vegetables such as broccoli and cabbage, and some fruits, particularly apricots and strawberries.^[5]

Secoisolariciresinol and matairesinol were the first plant lignans identified in foods. Pinoresinol and lariciresinol are more recently identified plant lignans that contribute substantially to the total dietary lignan intakes. Typically, lariciresinol and pinoresinol contribute about 75% to the total lignan intake whereas secoisolariciresinol and matairesinol contribute only about 25%.^[5] This distribution may change as the contributions of syringaresinol and hydroxymatairesinol have not properly been quantified in foods.

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Source	Amount per 100 g
Flaxseed	300,000 µg (0.3 g)
Sesame seed	29,000 µg (29 mg)
Brassica vegetables	185 - 2321 µg
Grains	7 - 764 µg
Red wine	91 µg

A recent study^[7] shows the complexity of mammalian lignan precursors in the diet. In the table below are a few examples of the 22 analyzed species and the 24 lignans identified in this study.

Mammalian lignan precursors as aglycones (µg / 100 g). Major compound(s) in bold.

Foodstuff	Pinoresinol	Syringaresinol	Sesamin	Lariciresinol	Secoisolariciresinol	Matairesinol	Hydroxymatairesinol
Flaxseed	871	48	not detected	1780	165759	529	35
Sesame seed	47136	205	62724	13060	240	1137	7209
Rye bran	1547	3540	not detected	1503	462	729	1017
Wheat bran	138	882	not detected	672	868	410	2787
Oat bran	567	297	not detected	766	90	440	712
Barley bran	71	140	not detected	133	42	42	541