Plant and mammalian lignans: A review of source, intake, metabolism, intestinal bacteria and health

Lignans are present in a wide range of foods consumed daily in the Western world such as flaxseed and other seeds, as well as vegetables, fruits and beverages such as coffee, tea and wine. Secoisolariciresinol diglucoside, a plant lignan, is metabolised to enterodiol and, then, to enterolactone. Matairesinol, another plant lignan, is also metabolised to enterolactone. Other dietary enterolignan precursors include lariciresinol, pinoresinol, medioresinol, syringaresinol, arctigenin and sesamin. Enterolignan-producing bacteria are common and accordingly enterolignans can be detected in the blood of most individuals; therefore, inter-individual differences in cell densities of the aforementioned bacteria may explain inter-individual differences in concentrations of enterolignan in blood. Research into the role of lignans in breast, colon and prostate cancer has generally shown they exert beneficial effects, although there are also some inconclusive studies or others that report negative effects. There are several possible mechanistic explanations for the observed bioactivities, including involvement in hormonal metabolism or availability, angiogenesis, anti-oxidation and gene suppression. Moreover, physiologically relevant concentrations of enterolignan have been shown to lead to “in vitro” and “in vivo” activation of oestrogen receptors.

► Lignans are found in a wide range of foods consumed daily worldwide.
► Enterolignans are detected in the blood of most individuals due to the presence of enterolignan-producing bacteria.
► The bioactivity of lignans depends on their transformation by gut bacteria.
► Epidemiological evidence indicates that enterodiol and enterolactone may be protective against certain chronic diseases.