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.
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%. This distribution may change as the contributions of syringaresinol and hydroxymatairesinol have not properly been quantified in foods.
|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 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.
|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|
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The body can synthesize most of the fats it needs from the diet. However, two essential fatty acids, linoleic and alpha-linolenic, cannot be synthesized in the body and must be obtained from food. These basic facts, found in plant foods, are used to build specialized fats called omega-3 and omega-6 fatty acids.1 Omega-3 and omega-6 fatty acids are important for the normal functioning of all tissues of the body.