Investigations into the health effects of whole flaxseed or flaxseed products (for example, defatted flaxseed meal, flax¬seed extracts) in human clinical trials and animal models have shown beneficial changes in blood lipid profiles and protection against some types of cancer. However, such studies do not show which flaxseed component(s) the benefits can be attributed, as flaxseed contains at least three components that are of health interest: soluble fibres or muci¬lage (about 6 % of dry weightp); high amounts of a-linolenic acid, an n-3 PUPA (about 20 % of dry weight); and the plant lignan secoisolariciresinol diglucoside , about 1 % of dry weight). Flaxseed also contains small amounts of other lignans, namely pinoresinol, lariciresinol and matairesinol, and although secoisolariciresinol diglucoside is the predominant lignan, the others may also contribute to health effects.
Flaxseed is the richest source of secoisolariciresinol diglucoside; however, the amount of secoisolariciresinol diglucoside 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.
Studies have shown that in defatted flaxseed extracts secoisolariciresinol diglucoside exists in oligomeric form largely in ester linkages to 3-hydroxy-3-methylglutaric acid(IO) and ¬cinnamic acid and .with other phenolic secoisolariciresinol diglucoside oligomers
The ability to quantify secoisolariciresinol diglucoside content in flaxseed extract sources enables an association to be drawn between secoisolariciresinol diglucoside amounts and the putative health effects of flaxseed lignans.
After ingestion, the plant lignan secoisolariciresinol diglucoside is converted to mammalian lignans by bacteria in the human colon. Secoisolariciresinol diglucoside first undergoes hydrolysis to yield the aglycone plant lignan secoisolariciresinol which is then converted to enter¬odiol (ED) and enterolactone (EL), first by dehydroxylation and demethylation to yield ED, which can then be oxidised to form EL(13) ED and EL can undergo further phase I and phase II biotransformation with extensive formation of glucuronide and sulfate conjugates(l4.IS), though the role of these metab¬olites in inducing biological effects is presently unknown.
The structural similarity of EL and ED to the most predomi¬nant and active form of oestrogen in the body, oestradiol, allows these lignans to bind to oestrogen receptors and exert weak oestrogenic or anti-oestrogenic effects’?’, However, the micromolar concentrations required to modulate oestrogen receptor activity in vitro is much higher than the serum EL and ED levels (nanomolar range) normally measured in the general populatio.
Nonetheless, recent studies provide scientific evidence of dietary sources of lignans as modulators of oestrogen receptor signalling in vivo
EL and ED also possess antioxidant activity.
Adolphe et al 2010 Health effects with consumption of the flax lignan secoisolariciresinol diglucoside British J Nutrition vol 103, 929-938
- Martin Eastwood