Lignans in Plant Based Foods

Lignans are polyphenolic compounds found in plant cell walls and seeds. They are classified as phytoestrogens because their metabolites (enterolignans) can bind weakly to oestrogen receptors in the body. The richest lignan sources include flaxseeds (~369 mg/100g), sesame seeds (~29 mg/100g), sunflower seeds (~3.4 mg/100g), and to lesser extents in whole grains, legumes, and vegetables. Flaxseeds are by far the dominant lignan source — a single tablespoon of ground flaxseed provides more lignans than most people consume from all other foods combined.

Secoisolariciresinol (SECO) is the primary lignan precursor found in flaxseeds and is the most abundant lignan precursor in the human diet. It exists in flaxseeds predominantly as secoisolariciresinol diglucoside (SDG), a glycosylated form. SDG accounts for approximately 95% of flaxseed lignans by weight. In the colon, bacterial β-glucosidase enzymes remove the glucose moieties, releasing aglycone SECO, which is then converted by gut microbiota into the bioactive enterolignans enterodiol and enterolactone.

Lignans are polyphenolic compounds that are chemically stable under normal food processing conditions. Grinding flaxseeds increases bioavailability by exposing lignans to digestive enzymes and gut bacteria, but does not destroy them. Cooking at moderate temperatures (baking, boiling) preserves lignans — they are not volatile like many essential oils. However, prolonged high-temperature processing (frying, roasting to very high temperatures) may cause minor oxidative losses. The most bioavailable flaxseed form is ground flaxseed, as the intact seed coat physically prevents bacterial access to lignans in the colon.