By Dr. Mercola
Lignans are a type of plant compound known as polyphenols. Lignan precursors are most abundant in flaxseeds, although they’re also found in other seeds (like sesame seeds), berries, fruits, vegetables, and whole grains.
When you consume lignan precursors, bacteria in your gut convert the “plant” lignans into “human” lignans, including enterodiol and enterolactone, which have weak estrogenic activity.
This can be beneficial for women’s health, because if you have naturally high estrogen levels, the weak “estrogens” from lignans may bind to some of your estrogen receptor sites, thereby actually reducing total estrogen activity. As explained by Dr. Christine Horner, a board certified general and plastic surgeon, who wrote an award-winning book on how to protect and fight breast cancer naturally:
“There are all sorts of different strengths to estrogens. Let's say estradiol, which is the strongest, most abundant form – if it hooks on to the estrogen receptor, it may cause a thousand cell divisions.
But if a plant estrogen hooks on, it may cause one. When you flood your system with these plant estrogens, I'd say it's kind of like a game of musical chairs.
There are only certain numbers of receptors, and whoever gets their first, gets it. They're blocking the strong estrogens from getting on, so that's why it has an inhibitory effect."
On the other hand, if your estrogen levels are low, lignans may help to supplement your levels to promote a more optimal balance. Its effect on hormonal balance is just one way these plant compounds may benefit your health.
Lignans May Help Fight Cancer
The anti-estrogenic effects of lignans (i.e. their ability to block the effects of estrogen in some tissues) could potentially help reduce the risk of hormone-associated cancers (breast, uterine, ovarian, and prostate).1 According to a review published in Critical Reviews in Clinical Laboratory Sciences:2
“Experimental evidence in animals has shown clear anticarcinogenic effects of flaxseed or pure lignans in many types of cancer.”
A meta-analysis of 21 studies similarly found high lignan exposure may be associated with a reduced breast cancer risk in postmenopausal women,4 and a study of thousands of Canadian women also revealed lignan-rich flaxseed intake is associated with a reduction in breast cancer risk.5
A study comparing the effects of sesame seed lignan and flaxseed lignan in reducing the growth of human breast tumors in mice revealed that sesame seed lignan reduced palpable tumor size by 23 percent compared to control and also increased apoptosis (programmed cell death).6
Both types of lignans also reduced tumor cell proliferation, but overall, the sesame seed lignan was more effective than the flaxseed lignan in reducing breast tumor growth.
Lignan-Rich Flaxseeds for Cancer Prevention?
Research has shown promising results related to flaxseeds (the richest dietary source of lignan precursors) and cancer. As reported by the University of Maryland Medical Center:7
“… [P]ostmenopausal women who were newly diagnosed with breast cancer ate a muffin with 25 grams dietary flaxseed every day for 40 days. The study found that adding flaxseed to the diet may have the potential to reduce tumor growth in women with breast cancer.
… Animal studies show that lignans may slow the growth of colon tumor cells. Population studies suggest that flaxseed may reduce the number of abnormal cell growths, which are early markers of colon cancer.”
Further, according to Dr. Horner, there are hundreds of studies showing that flax not only protects against breast cancer more effectively than any other food we know of but may also shrink breast tumors.
She also cites research by Lilian Thompson of the University of Toronto, who has done many studies on flaxseeds and estrogen-positive tumors. In one of Dr. Thompson’s studies, she found that estrogen-positive breast tumors shrank in every woman given flaxseeds for three weeks.
“I had personal experience with this,” Dr. Horner said. “My business manager’s mother developed breast cancer.
I started her on three tablespoons of flaxseed per day, plus a potent herbal antioxidant. Her tumor was 1.5 cm on mammogram. At the time of surgery three weeks later her tumor had shrunk to 0.5 cm.
With all these cancer-fighting effects, not surprisingly, research shows that women who have the highest level of lignans in their body have the lowest risk of breast cancer.
Flaxseeds contain 100 times more lignans than any other known plant source and are one of the most powerful foods you can eat to lower your risk of breast cancer.
Here’s the key to understanding this controversy: Plant estrogens are not the same as the estrogens your body makes or synthetic estrogens found in hormone replacement therapy.
They are very different. Many actually act more like selective estrogen modulators or SERMS (Tamoxifen is a SERM) and as aromatase inhibitors like Arimidex. These plant chemicals act in so many complex ways that we may never fully understand them all.”
Dr. Thompson’s and others' research show that flax lignans fight breast cancer: in a number of ways, including:
Lowering your overall production of estrogen Blocking environmental estrogens from attaching to breast tissue Creating more of a "good" protective type of estrogen Protecting your breast tissue from the damaging effects of environmental toxins Decreasing three different growth factors associated with the growth of breast cancer Blocking the aromatase enzyme in a way similar to the drug Arimidex Lengthening your menstrual cycle Blocking the estrogen receptor in a way similar to the drug Tamoxifen
Heart Health Benefits of Lignans
Aside from cancer, there is evidence that eating a diet rich in plant lignans may be linked to a lower risk of heart disease. In a study of nearly 2,000 men, those with the highest enterolactone levels, which are a marker of plant lignan intake, were significantly less likely to die from coronary heart disease than those with the lowest levels.8,9
Research also shows that adding flaxseeds to your diet may have a favorable effect on cholesterol levels, although it’s unknown at this time if that’s due to the lignans or other heart-healthy nutrients or phytochemicals found in flaxseeds (such as plant-based omega-3s or fiber).10
In a study that also compared flaxseed lignans with sesame seeds lignans, the sesame seed lignans appeared to lower TBARS (Thiobarbituric Acid Reactive Substances) concentration and increase vitamin E while the flaxseed lignans did not.11 Increased levels TBARS are associated with diseases such as atherosclerosis, heart disease, diabetes, liver disorders, and inflammatory rheumatic diseases.
Potential Bone Health and Antioxidant Effects
It’s known that phytoestrogens’ estrogenic effects in bone could help maintain bone density. In the case of osteoporosis, research suggests enterolactone excretion (a marker of dietary lignan intake) was positively associated with bone mineral density in the spine and hip of postmenopausal women, although more research is needed in this area.12
It is also suggested that lignan precursors may have beneficial effects that are unrelated to its interactions with estrogen receptors. Among these are potential antioxidant effects. According to the Linus Pauling Institute:13
“Lignans can act as antioxidants in the test tube, but the significance of such antioxidant activity in humans is not clear because lignans are rapidly and extensively metabolized. Although one cross-sectional study found that a biomarker of oxidative damage was inversely associated with serum enterolactone levels in men, it is not clear whether this effect was related to enterolactone or other antioxidants present in lignan-rich foods.”
What Are the Best Food Sources of Lignans?
Seeds (flax, pumpkin, sunflower, poppy, and sesame), berries, and vegetables are among the best food sources of lignans. Flaxseed is the richest dietary source and crushing the seeds may improve lignans’ bioavailability. However, because flaxseeds are highly perishable and turn rancid rapidly, you should buy organic whole seeds, and grind them yourself just prior to use (avoid pre-ground versions). Flaxseed oil does not typically contain lignans.
In the US, consumption of phytoestrogens such as lignans is low. It’s thought the average intake for postmenopausal women is less than 1 milligram (mg) a day, with 80 percent of that from lignans. You may need to consume between 50 and 100 mg of lignans a day to raise enterolactone to beneficial levels, which is the equivalent of three or four tablespoons of unrefined ground flaxseed per day. You can also find beneficial lignans in supplement form. If you’d like to increase your dietary intake, the chart below, from the Linus Pauling Institute, shows the total lignan content of a variety of foods:14
Total Lignan Content of Selected Foods Food Serving Total Lignans (mg) Flaxseeds 1 oz 85.5 Sesame seeds 1 oz 11.2 Curly kale ½ cup, chopped 0.8 Broccoli ½ cup, chopped 0.6 Apricots ½ cup, sliced 0.4 Cabbage ½ cup, chopped 0.3 Brussels sprouts ½ cup, chopped 0.3 Strawberries ½ cup 0.2