Flax lignans: new opportunities for functional foods

Flaxseed (Linum usitatissimum) is the richest dietary source of the lignan secoisolariciresinol (SECO), a diphenolic compound that when ingested by humans influences a wide range of biological systems that help keep humans healthy. SECO, which is present in the seed coat as an ester of its diglucoside, is absorbed intact or can undergo bioconversion in the colon to a range of mammalian lignans including enterodiol and enterolactone, which are in turn also absorbed. These compounds have antioxidant properties; they are competitive binders to hormone receptors and proteins such as sex hormone binding globulin, and they influence health outcomes through their effects on gene expression. Clinical trials have shown that administration of lignan extracts significantly reduces serum cholesterol levels in hypercholesterolaemic subjects, has beneficial effects on subjects with benign prostatic hyperplasia and may have beneficial effects on glucose metabolism. Clinical trials with flaxseed, and animal studies with flaxseed and lignan extracts, have also indicated beneficial effects in terms of risk reduction for hormone-dependent cancers such as breast and prostate cancer, and a potential role in delaying progression of these cancers. Epidemiological studies of lignan exposure and cancer risk have shown that modest risk reduction is associated with lignan intake; however, these studies are not capturing the effect of even a very modest intake of flaxseed. Flaxseed and/or flaxseed meal has been incorporated into a wide range of functional foods, including breads, pasta, nutrition bars and breakfast cereals. (Authors abstract)
Flaxseed is relatively unique among grains and oilseeds because it contains a unique combination of nutrients including a very high omega-3 fatty acid content of the oil. Flax is a rich source of polysaccharide mucilage, sometimes referred to as gum or soluble fibre. Flaxseed is a good source of insoluble fibre. Flaxseed is also a rich source of phytochemicals, many of which have potentially useful biological activity in humans. The subject of this review is the lignan secoisolariciresinol (SECO). The science supporting the health benefits of SECO and SDG is beginning to grow. The lignan complex and SDG-enriched materials are now available in sufficient quantities to undertake human clinical trials, and these studies are indicating that lignans, in particular SDG/SECO, have significant potential to become important functional ingredients in functional foods. The potential for flax lignans as functional ingredients to reduce risk of developing hormone-dependent cancer is less clear because most of the evidence to date comes from animal studies. The limited number of dietary intervention studies conducted to date has shown that these risk analysis studies have all focused on populations with very low EL levels relative to what can be achieved with only a modest intake of flax lignans. The limited amount of clinical evidence available so far would suggest that when risk analysis studies are undertaken that include a significant number of people with a regular intake of flax lignans, a stronger association between dietary lignan intake and reduced risk of hormone-dependent cancers as well as beneficial effects in maintaining a healthy cardiovascular system. (Editors comments)