The lignans are a large group of low molecular weight

polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...

s found in

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

s, particularly seeds,

whole grain A whole grain is a grain of any cereal and pseudocereal that contains the endosperm, germ, and bran, in contrast to refined grains, which retain only the endosperm. As part of a general healthy diet, consumption of whole grains is associated w ...

s, and vegetables. The name derives from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word for "wood". Lignans are precursors to

phytoestrogen A phytoestrogen is a plant-derived xenoestrogen (see estrogen) not generated within the endocrine system, but consumed by eating plants or manufactured foods. Also called a "dietary estrogen", it is a diverse group of naturally occurring nonstero ...

s. They may play a role as

antifeedant Antifeedants are organic compounds produced by plants to inhibit attack by insects and grazing animals. These chemical compounds are typically classified as secondary metabolites in that they are not essential for the metabolism of the plant, but i ...

s in the defense of seeds and plants against

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

Biosynthesis and metabolism

Lignans and

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

differ in their molecular weight, the former being small and soluble in water, the latter being high polymers that are undigestable. Both are

ic substances derived by oxidative coupling of

monolignol Monolignols, also called lignols, are the source materials for biosynthesis of both lignans and lignin and consist mainly of paracoumaryl alcohol (H), coniferyl alcohol (G) and sinapyl alcohol (S). These monolignols differ in their degree of meth ...

s. Thus, most lignans feature a C₁₈ cores, resulting from the dimerization of C₉ precursors. The coupling of the lignols occurs at C8. Eight classes of lignans are: "furofuran, furan, dibenzylbutane, dibenzylbutyrolactone, aryltetralin, arylnaphthalene, dibenzocyclooctadiene, and dibenzylbutyrolactol." Many lignans are metabolized by mammalian gut microflora, producing so-called

enterolignan Enterolignans are organic compounds formed by the action of gut microflora on lignan The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables. The name derives from the L ...

Food sources

Flax seed Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known in W ...

s and

sesame seed Sesame ( or ; ''Sesamum indicum'') is a flowering plant in the genus ''Sesamum'', also called benne. Numerous wild relatives occur in Africa and a smaller number in India. It is widely naturalized in tropical regions around the world and is cu ...

s contain high levels of lignans. The principal lignan precursor found in flaxseeds is

secoisolariciresinol diglucoside Secoisolariciresinol diglucoside (SDG) is an antioxidant phytoestrogen present in flax, sunflower, sesame, and pumpkin seeds. In food, it can be found in commercial breads containing flaxseed. It is a precursor of mammal lignans which are pro ...

. Other foods containing lignans include cereals ( rye,

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

oat The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other cereals and pseudocereals). While oats are suitable for human con ...

and

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...

tofu Tofu (), also known as bean curd in English, is a food prepared by coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness; it can be ''silken'', ''soft'', ''firm'', ''extra firm'' or ''super f ...

cruciferous vegetables Cruciferous vegetables are vegetables of the family Brassicaceae (also called Cruciferae) with many genera, species, and cultivars being raised for food production such as cauliflower, cabbage, kale, garden cress, bok choy, broccoli, Brussels spr ...

, such as

broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the cabbage family (family Brassicaceae, genus ''Brassica'') whose large flowering head, stalk and small associated leaves are eaten as a vegetable. Broccoli is cl ...

and

cabbage Cabbage, comprising several cultivars of ''Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage ( ''B.&nb ...

, and some fruits, particularly apricots and

strawberries The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...

. Lignans are not present in

seed oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fa ...

, and their contents in whole or ground seeds may vary according to geographic location, climate, and maturity of the seed crop, and the duration of seed storage. Secoisolariciresinol and matairesinol were the first plant lignans identified in foods. Typically, lariciresinol and pinoresinol contribute about 75% to the total lignan intake, whereas secoisolariciresinol and matairesinol contribute only about 25%. Foods containing lignans:

Prevalence and Health Effects

Lignans are the principal source of dietary

s in typical

Western diet The Western pattern diet is a modern dietary pattern that is generally characterized by high intakes of pre-packaged foods, refined grains, red meat, processed meat, high-sugar drinks, candy and sweets, fried foods, conventionally-raised anim ...

s, even though most research on phytoestrogen-rich diets has focused on

soy The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu and ...

isoflavones. Lignan's

products

enterodiol Enterodiol is an organic compound with the formula OC6H4CH2CH(CH2OH)sub>2. It is formed by the action of intestinal bacteria on lignan precursors. As such it is sometimes classified as a enterolignan Enterolignans are organic compounds formed ...

and

enterolactone Enterolactone is a organic compound classified as an enterolignan. It is formed by the action of intestinal bacteria on plant lignan precursors present in the diet. Sources Many dietary plant lignan precursors, such as secoisolariciresinol, mat ...

have weak estrogenic activity, but they may also exert biological effects through non-estrogenic means. A 2021 review found that lignans have a positive effect on lipid profiles of patients with

dyslipidemia Dyslipidemia is an abnormal amount of lipids (e.g. triglycerides, cholesterol and/or fat phospholipids) in the blood. Dyslipidemia is a risk factor for the development of atherosclerotic cardiovascular disease ( ASCVD). ASCVD includes coronary ar ...

related diseases. As of 2022 there is limited evidence that dietary intake of lignans is associated with a reduced cancer and cardiovascular disease risk.

References

External links

IUPAC lignan nomenclature
{{Lignan

Biosynthesis and metabolism

Food sources

Prevalence and Health Effects

See also

References

External links