What are lignans?
Plant lignans are one of the four classes of phytoestrogens (isoflavones, lignans, stilbenes, coumestans), phenolic compounds that are structurally similar to the main mammalian estrogen, estradiol.1 Plant lignans are modified by bacteria in the human digestive tract into enteroligans. It is important to recognize the role of healthy bacteria in this process, because antibiotics can destroy beneficial bacteria in the gut resulting in long-term reduction in enteroligans.2 Eating commercial meats exposes us to antibiotics, as does the overuse and inappropriate prescribing by physicians.
Which foods are good sources of plant lignans?
Flaxseeds are the richest source of plant lignans, having about 8 times the lignan content of sesame seeds [note that flaxseed oil does not contain lignans – they bind to the fiber]. The other plant foo ds on the list have about one-tenth or less the amount of lignans as sesame seeds per serving.2,3 Chia seeds are also a rich source of lignans, however the exact amount is still debatable, so that number will be made available at a later date.
- Flaxseeds (85.5 mg/ounce)
- Sesame seeds (11.2 mg/ounce)4
- Kale (curly; 1.6 mg/cup)
- Broccoli (1.2 mg/cup)
Anti-cancer effects of lignans
Enterolignans are structurally similar to estrogen and can bind to estrogen receptors – this capability allows lignans to either have weak estrogenic activity or block the actions of estrogen in the body. For this reason, plant lignans are classified as phytoestrogens, and there has been much interest in the potential contribution of lignan-rich foods to reduced risk of hormone-related cancers.2,5 Enterolignans inhibits aromatase6 and estradiol production in general, lowering serum estrogen levels.7 Plant lignans also increase concentration of sex hormone binding globulin, which blunts the effects of estrogens.8-10 These benefits were documented when 48 postmenopausal women consumed 7.5 g/day of ground flax seeds for 6 weeks, then 15 g for 6 weeks – and significant decreases in estradiol, estrone, and testosterone w ere noted with a bigger decrease in overweight and obese women.11
In a mouse model, a flaxseed diet (5%, 10%) shows dose-dependent inhibition of breast tumor growth.12 Human trials also confirmed similar beneficial effects. A double-blinded, randomized controlled trial of dietary flaxseed demonstrated dramatic protection. Women ate either a control muffin with no flax seeds imbedded or 25g flax-containing muffin starting at time of diagnosis of breast cancer for just 32-39 days until surgery. Tumor tissue analyzed at diagnosis and surgery demonstrated surprising benefits even in this short timeframe. There was a significant apoptosis (tumor cell death) and reduced cell proliferation in the flaxseed group in just the one month.13 Likewise women eating more flaxseeds with a documented higher serum enterolactone were found to have a 42% reduced risk of death from postmenopausal breast cancer and a dramatic (40 percent) reduction in all causes of death.14,15 Flaxseeds are clearly super foods; even with a mediocre diet they offer powerful protection against certain types of breast cancer. Another interesting study on flax followed women for up to 10 years and found a 51% reduced risk of all-cause mortality and a 71% reduced risk of breast cancer mortality. The intake of dried beans was also associated with a 39% reduced risk of all-cause mortality.16 Endometrial and ovarian cancer have not been as extensively studied, but the few studies that have been conducted suggest a protective effect.2,17
Bottom line; don’t forget to take your ground flax seeds (or chia seeds) every day. I sometimes forget too, but reviewing the science encourages me to remember. When used in conjunction with dietary exposure to greens, onions, mushrooms and beans, dramatic reductions in the risk of breast cancer are possible.
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Dr. Fuhrman’s newest book, Super Immunity, addresses his full nutritional program to win the war against breast cancer.
1. Mense SM, Hei TK, Ganju RK, et al: Phytoestrogens and breast cancer prevention: possible mechanisms of action. Environ Health Perspect 2008; 116:426-433.
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11. Sturgeon SR, Heersink JL, Volpe SL, et al: Effect of dietary flaxseed on serum levels of estrogens and androgens in postmenopausal women. Nutr Cancer 2008;60:612-618.
12. Chen J, Power KA, Mann J, et al: Flaxseed alone or in combination with tamoxifen inhibits MCF-7 breast tumor growth in ovariectomized athymic mice with high circulating levels of estrogen. Exp Biol Med (Maywood) 2007;232:1071-1080.
13. Thompson LU, Chen JM, Li T, et al: Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res 2005;11:3828-3835.
14. Buck K, Vrieling A, Zaineddin AK, et al: Serum enterolactone and prognosis of postmenopausal breast cancer. J Clin Oncol 2011;29:3730-3738.
15. Buck K, Zaineddin AK, Vrieling A, et al: Estimated enterolignans, lignan-rich foods, and fibre in relation to survival after postmenopausal breast cancer. Br J Cancer 2011;105:1151-1157.
16. McCann SE, Thompson LU, Nie J, et al: Dietary lignan intakes in relation to survival among women with breast cancer: the Western New York Exposures and Breast Canc er (WEB) Study. Breast Cancer Res Treat 2010;122:229-235.
17. Bandera EV, King M, Chandran U, et al: Phytoestrogen consumption from foods and supplements and epithelial ovarian cancer risk: a population-based case control study. BMC Womens Health 2011;11:40.
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