Dietary intake and major sources of plant lignans in Latvian men and women.

Higher intake of lignans, diphenolic plant compounds, may reduce the risk of certain types of cancer and cardiovascular diseases. We assessed the dietary intake of four lignans: matairesinol, secoisolariciresinol, lariciresinol and pinoresinol. Furthermore, for the breads we supplemented the data with two more lignans: syringaresinol and medioresinol. Study subjects were 172 men and 97 women aged 40 to 75 years, residing in Riga, the capital of Latvia, all living at home, eating habitual food. Median total lignin intake was 2259 (range 1169 to 5759) mg/day. Secoisolariciresinol contributed 58% and syringaresinol 22% of lignan intake. Bread was the major food source of lignans in men (86%), whereas in women it was bread (57%) and flaxseed (35%). (Authors abstract)

Phytoestrogens are natural plant substances or metabolites of plant precursor that are structurally and functionally comparable to endogenous estrogens and can have both estrogenic and antiestrogenic effects and they can be considered as natural selective estrogen receptor modulators. Moreover, phytoestrogens can also have antioxidative and antiproliferative properties. Predominantly, lignans are the most important sources of phytoestrogens in western diet.  After consumption, plant lignans can be partially absorbed or further metabolized by the intestinal microbiota into the ‘enterolignans’ enterolactone (ENL) and enterodiol (END).  It was long assumed that only two plant lignans, secoisolariciresinol (SECO) and matairesinol (MAT), were the dietary precursors of enterolignans. More recently, many other precursors of enterolignans were discovered, such as lariciresinol (LAR), pinoresinol (PIN), medioresinol (MED), syringaresinol (SYR) as well as 7 hydroxymatairesinol (HMR), arctigenin (ARC) and sesamin (SES).

This study describes the intake of four major lignans (SECO, MAT, LAR, PIN) in a group of Latvian men and women. Also, other lignans, such as SYR and MED, were assessed, but only in bread samples. In the context of the studies where six lignans were analysed, median lignan intake was lower than in Swedish men but higher than in Swedish women (Hedelin et al. 2008).Within lignans, the highest median daily intake of SECO was associated with lower PIN, LAR and MAT intake, being consistent with Canadian and Italian data but not with other studies where the most important contributors were LAR and PIN. In this study, the intake of plant lignans for men was explained by the intake of grain products (86%), and predominantly bread intake. Flaxseed was a moderately significant food source of lignans for women (35%), while for Canadian women it was the major source (88%). The intake of lignans correlated with intake of dietary fibre, which is explained by the fact that major source of lignan intake was fibre rich bread and linseeds. The strength of our study is that it included intake of four major lignans and six lignans regarding breads which improves estimation of lignans compared with a commonly used assay of only two lignans. By using the FFQ, it is possible to reflect long term dietary habits, which is more significant than lignan intake over a few days.  This study found a high dietary intake of lignans in this study population of middle-aged and elderly Latvian men and women. SECO was the main contributor of assessed lignans. The main dietary sources of lignans were breads, which contain moderate amounts of lignans, but are consumed on a daily basis, and flaxseed, which is a rich source of lignans, but was consumed by minor part of population. The potential disease-protective effects of lignans could be diminished in this population by the high fat intake detected. (Editors comments)