Lignans are compounds found mainly in whole grains, vegetables and seeds. Plants use them as defense weapons against threats like herbivores or pathogens. Bitter, tough or toxic, they can also affect human health.
Lignans are polyphenols, organic compounds made of phenols such as tannins. Lignans support the health of plants. The term "lignan" is from the Latin for "wood," referring to their abundance in woody plants.
There are over 30 known types of lignan. They include
Secoisolariciresinol
The water extract of silver fir wood contains over 5% secoisolariciresinol, which is also present in nettle tea. In flaxseed (Linum usitatissimum), it's found at 0.3%, the highest known concentration in food.
Matairesinol
It is present in some cereals, such as rye. Medical claims range from anticarcinogen to cardiovascular effects. Research is ongoing.
Pinoresinol
Claims include possible blood sugar reduction. Expense of extraction can deter medical sponsors. It's also a potential inhibitor of Vitamin D uptake.
Plant lignans are converted into enterolignans by intestinal microbes in the human body. Without bacterial intervention humans cannot digest lignans. Poor digestion can inhibit the uptake of nutrients.
Lignans are phytoestrogens, considered to mimic estrogen's effects on the human body. They are concentrated in foods like flaxseeds, sesame seeds and whole grains like barley and rye.
Lignans: The Plant Protectors
Lignans enable plants to thrive in competitive ecosystems. Plants produce lignans as antifeedants, a defense against predation by herbivores. Lignans make the plant taste noxious or cause digestive problems, discouraging bacteria, bugs, browsers and grazers.
Occasionally insects use lignans to their own advantage. Pinoresinol is part of defensive secretions produced by glandular hairs of caterpillars of the cabbage butterfly, Pieris rapae.
Flax has about 75% of its lignans in the seeds. This strong concentration helps repel insects, giving flax an advantage over other plants.
The relationship between this plant and humans goes back thousands of years. Its fibers are used to make linen, the first known textile. Flax fibers 35,000 years old are found in cave dwellings. Linen fabric is discovered at Neolithic Çatalhöyük.
Sesame seeds are also known for their high lignan content, particularly sesamin and sesaminol. They're promoted for anti-inflammatory and antioxidant benefits. Sesaminol has been used in fat reduction medication.
Some research posits various health benefits.
Antioxidant Effects: Lignans are considered to combat oxidative stress by neutralizing free radicals.
Hormonal Manipulation: Due to their estrogen-like properties, lignans are recommended to symptomatic women in stages of menopause. Hormone manipulation can be a controversial subject.
Cognitive Health: There is a suggested link between lignan consumption and better cognitive function in older adults.
Digestive Benefits: Lignans are believed to improve digestive tract health by fortifying the composition of some bacteria.
Flaxseed has high amounts of secoisolariciresinol diglucoside (SDG). This substance slows human breast cancer in mice but may reduce survival rates for some human brain tumor patients.
Difference Between Lignans & Lignin
Lignans and lignin have the same Latin root and are both derived from plants. Lignins are complex polymers, part of the structural framework of plants, especially trees. They fortify rigidity and decay resistance.
Lignins are major components of cell walls, especially in woody plants, and have essential functions in water transport and mechanical support.
Lignans are secondary metabolites in plants.
Lignins contribute to plant health by reinforcing structure and integrity. Lignans are smaller compounds, naturally involved in more targeted plant defense.
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