August 02 2021
Lignans are composed of compounds called polyphenols predominantly found in plants. The precursors of lignans are available in a large variety of food derived from plants such as legumes, whole grains, seeds, fruits and vegetables. Flaxseeds are the most abundantly known dietary source of lignans. On consumption of lignans, they get converted by bacteria that usually colonise in the human intestinal tract into enterolignans, enterodiol and enterolactone. The compounds enterodiol and enterolactone, even though possess weak estrogenic activity, play an integral role in the functioning of biological activities through non-estrogenic mechanisms. Foods which are rich in lignans constitute a healthy dietary pattern and the importance of lignans is being researched in the prevention of hormone associated diseases.
On ingestion, plant lignans are metabolised into enterolactone, enterodiol and enterolignans by the intestinal bacteria inside the intestinal lumen. The amount of serum enterolactone levels has been linked to antibiotic use. The dietary intake of plant lignans and the activity of intestinal bacteria is determined by the levels of enterolactone in the serum and urine thereby used as a marker of dietary lignan intake. The difference in the metabolism of lignans which may be due to the action of gut microbes leads to different biological activities and the health effects of these compounds from individual to individual.
Biological activities of lignans
- Estrogenic and anti-estrogenic action
Estrogens are known as signalling compounds which showcase their effects by binding to the various estrogen receptors present within the cells. This estrogen receptor complex is formed in association with the DNA and causes modifications in the expression of estrogen-responsive genes. Other than the issues associated with reproduction, the estrogen receptors are present in various other tissues such as bone, liver, heart and brain. Compounds called phytoestrogens also can bind to the estrogen receptors even though their estrogenic activity is a lot less effective than the endogenous estrogens and this mechanism of action may lead them to antagonise the effects of estrogen in some selective tissues.
This action of tissue-specific phytoestrogens is being under intense experimental research as its anti-estrogenic effects which are demonstrated in the reproductive tissues can be responsible in reducing the risk of hormone associated with breast, uterine, ovarian and prostate while its action in the bone could help in maintaining the bone density.
- Estrogen receptor independent activity
There are many mechanisms of action of enterolignans which are also independent of their estrogen receptors. By suitable modification in the activity of the enzymes associated with estrogen metabolism, lignans are involved in changing the biological activity of these endogenous estrogens. Lignans are rapidly and extensively metabolised and also act as antioxidants, hence they act as biomarkers of oxidative damage which is inversely linked with serum enterolactone levels in the body.
- Prevention of cardiovascular disease
Foods which are a good source of lignans such as whole grains, nuts, seeds, legumes, fruits and vegetables are known to be associated with a decreased risk of cardiovascular disease. Studies show that those with increased serum enterolactone levels, which is a marker for plant lignan intake, have significantly less mortality in cardiovascular disease. Flaxseeds, being one of the richest sources of plant lignans, are also very good sources of various other nutrients which exhibit cardioprotective effects such as omega -3 fatty acids and fibre. Studies show that the flaxseed supplements like Alvizia healthcare flaxseed oil capsules result in a decrease in the levels of LDL cholesterol in those with a high risk of cardiovascular disease and menopausal women thereby demonstrating the cardioprotective action of lignans.
Urinary enterolactone elimination is used as a marker of dietary lignan intake in these studies. In postmenopausal women, urinary enterolactone excretion is positively linked with the bone mineral density of the lumbar spine and hip which shows the rate of bone loss and can be used in determining whether the bone can be classified as osteoporotic, osteopenic or normal thus examining the chance of developing osteoporosis in such women. Supplementing with flaxseeds in these conditions is shown to significantly alter the biochemical markers of bone formation and prevent bone loss.
- Effects on blood pressure
Lignans are known to have a positive impact on systolic blood pressure. The higher the pressure of the blood in the arteries as the heart contracts, the higher is the risk of developing cardiovascular disease. Daily intake of lignans shows a significant decrease in systolic blood pressure. Daily flaxseed consumption is also known to be beneficial in cutting hypertension.
- As a great source of proteins, lignans are known to enhance immune function, lower cholesterol levels, prevention of tumours and significant anti-fungal properties. They also contribute to the feeling of fullness which results in eating less in the next meal thereby preventing weight gain.
- In those with type 2 diabetes which is characterised by increased blood sugar levels because of the body’s inability to secrete insulin, adding lignans to the daily diet slows down the release of sugar into the blood, therefore, decreases the blood sugar levels in the body.