Flaxseed is the richest source of the lignan secoisolariciresinol diglucoside (SDG). After ingestion, SDG is converted to secoisolariciresinol, which is further metabolised to the mammalian lignans enterodiol and enterolactone. A growing body of evidence suggests that SDG metabolites may provide health benefits due to their weak oestrogenic or anti-oestrogenic effects, antioxidant activity, ability to induce phase 2 proteins and/or inhibit the activity of certain enzymes, or by mechanisms yet unidentified. Human and animal studies identify the benefits of SDG consumption. SDG metabolites may protect against CVD and the metabolic syndrome by reducing lipid and glucose concentrations, lowering blood pressure, and decreasing oxidative stress and inflammation. Flax lignans may also reduce cancer risk by preventing pre-cancerous cellular changes and by reducing angiogenesis and metastasis. Thus, dietary SDG has the potential to decrease the incidence of several chronic diseases that result in significant morbidity and mortality in industrialised countries. The available literature, though, makes it difficult to clearly identify SDG health effects because of the wide variability in study methods. However, the current evidence suggests that a dose of at least 500 mg SDG/d for approximately 8 weeks is needed to observe positive effects on cardiovascular risk factors in human patients. Flaxseed and its lignan extracts appear to be safe for most adult populations, though animal studies suggest that pregnant women should limit their exposure. The present review discusses the potential health benefits of SDG in humans, with supporting evidence from animal studies, and offers suggestions for future research.
Secoisolariciresinol diglucoside: Flax lignans: Health benefitsInvestigations into the health effects of whole flaxseed or flaxseed products (for example, defatted flaxseed meal, flaxseed extracts) in human clinical trials and animal models have shown beneficial changes in blood lipid profiles (1,2) and protection against some types of cancer (3,4) . However, such studies cannot reveal to which flaxseed component(s) the benefits can be attributed, as flaxseed contains at least three components that are of health interest: soluble fibres or mucilage (about 6 % of dry weight) (5) ; high amounts of a-linolenic acid, an n-3 PUFA (about 20 % of dry weight) (6) ; and the plant lignan secoisolariciresinol diglucoside (SDG, about 1 % of dry weight) (7) . Flaxseed also contains small amounts of other lignans, namely pinoresinol, lariciresinol and matairesinol (8) , and although SDG is the predominant lignan, the others may also contribute to health effects.Flaxseed is the richest source of SDG (9) ; however, the amount of SDG in flaxseed varies between different cultivars and in most studies that examined the health effects of flaxseed or its products, the concentration of lignans was not determined. With the development of HPLC technology, SDG can be extracted from flaxseed and its SDG content determined (7) . Subsequent studies...