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Does eating flaxseed prevent or raise cancer risk?

Have you noticed more and more products with flaxseeds in your local market? The tiny brown and golden seeds have similar estrogen-like compounds found in soy. So are flaxseeds safe to eat, and particularly for people with a higher risk of hormonal cancers?

Cancer develops for an array of reasons, but there are opportunities along the way to possibly slow or prevent growth. Nutrition is one such opportunity. Of special consideration are compounds found in plant foods, and most intriguing, are the cancer-preventative nutrients in flaxseed.

One group of astounding anticancer compounds are a type of phytochemical called lignan. And flaxseed just happens to be the richest source of lignans.

For years, a powerful phytoestrogen—or plant estrogen— found in plant foods such as soy and flaxseed were thought to promote cancers fueled by estrogen, especially ER-positive breast cancer. But the types of estrogen made from plants have now been found to decrease the risk of several cancers, along with other health benefits. 

Breads baked with flaxseed

Add flaxseed to batter when baking bread or muffins

Flaxseed is among the plant foods with cancer preventative advantages, slowing tumor growth, raising the body's defense systems with antioxidants, and promoting normal cell growth—the opposite of cancer growth. Lignans, a phytoestrogen in flaxseed, are now associated with a decreased risk of breast cancer, colon and lung cancer, and possibly prostate, but more studies are still needed. How do we know this?

Researchers followed over 58,000 postmenopausal women in France and those who ate the highest amounts of lignan ingestion (more than 5 ounces a day), were found to significantly decrease their risk of ER+ and PR+ breast cancer. Breast cancers which have estrogen or progesterone receptors rely on these hormones to grow.

In other studies, women who took flaxseed lignans for a year showed a smaller amount of precancerous changes in the breast, or had less aggressive type cancers. Flaxseed may work together with the aromatase inhibitor medication tamoxifen to slow breast tumor growth. "This approach—adding flaxseeds to the diet—looks promising, " says the Oncology Dietetic Practice Group of the Academy of Nutrition and Dietetics. Yet, other studies have not shown an effect.

Whole toasted, flaxseed

Whole, toasted flaxseed

How do lignans prevent cancer? Lignans bind to estrogen receptors, and in postmenopausal women, lignans can produce less active forms of estrogen. Lignans are anti-inflammatory, and inhibit tumor growth by killing off abnormal cells. This process may be blocked in cancer cells. Lignans work to prevent the rapid, out-of-control growth spikes of cancer cells. Moreover, flaxseed steadies blood sugar.

Flaxseed contains two types of phytochemicals: lignans (a phytoestrogen) found in high fiber plant foods like seeds, and lignins. Lignans and whole grains have been found to reduce colon cancer; while lignins reduce inflammation, and boost the immune system. 

Whole grains, nuts, seeds, fruits, vegetables, and beans also provide lignans. People who eat more plant foods eat more lignans, reducing their breast cancer risk. Lignans are metabolized by the gut bacteria to release its active components. We need more diverse species of bacteria to handle these foods, and plant foods are a tasty way to provide food for the bacteria in our gut. 

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How much flaxseed is enough to reduce cancer risk? 2 tablespoons daily, or 32 g, may reduce breast cancer risk. Up to 2-3 tablespoons of ground flaxseed a day is safe for those at higher risk of cancer. Start slow: 1 tablespoon of ground flaxseed per day, then add more after a few days, to allow the body to adjust to the increased fiber. Use ground flaxseed, or flaxseed meal, to get maximum nutrition, according to The Natural Medicines Comprehensive Database.

As for other health benefits of interest: Flaxseed is the best source of boron for bone health; and reduces cholesterol due to its soluble fiber. 1 tbsp of whole flaxseed has 2.8 g of fiber. The fiber may be less fermentable than other fibers, but no less useful. Softer, larger stools leads to less transit time and means your colon has less contact with toxins. There is more protein in a 1/4 cup of ground flaxseed (5.1 g) than beans, but we do eat a lot less flaxseed than beans. 

Whole flaxseed

Whole flaxseed

When ground, flaxseed is high in alpha-linolenic acid (ALA) and a small amount is converted to omega-3s (whole seeds only pass undigested through the intestinal system). Flaxseed oil also has omega-3s, but not the additional benefits of lignans or fiber. 

Who should not eat flaxseed? Flaxseed may bind to medications and interfere with absorption:

  • Don't take flaxseed together with medications or supplements.

  • The Oncology Dietetic Practice Group says cancer patients and survivors talk to your doctor or dietitian first, before adding flaxseeds to your diet.

  • The Natural Medicines Comprehensive Database and National Center for Complementary and Integrative Health (NCCIH) of the NIH recommends avoiding flaxseed and flaxseed oil during pregnancy and breastfeeding because of mild hormonal effects. 

  • People who take high doses of EPA and DHA supplements or medications with anticoagulant effects, should talk with their doctor before beginning daily flaxseed use, and what amounts are safe.

  • Finally, flaxseed will interfere with thyroid regulation if you are deficient in iodine or have thyroid conditions, and should not be eaten.

Whole flaxseed is cheaper than ground, and you can grind it yourself in a coffee grinder. It's best to eat it cooked at lower temperatures rather than raw. You can mix it with flour, add it to dough or batter, toast it and add to puddings, oatmeal, and smoothies. Flaxseeds can also be sprouted. Once ground, keep frozen because the omega-3 fatty acids are unstable.

Make sure to eat ground flaxseed with plenty of water. Flaxseed can have a laxative effect, or worsen constipation, because it has the same soluble fiber as oat bran. It may rarely cause intestinal blockage.

And if you're not partial to flaxseed, guess what? All of these beneficial phytochemicals and anticancer benefits, whether lignans or lignins, are also found in soyfoods.

Subscribe! Get continuous updates on nutrition for cancer survivors. Click the button at top of page, and you'll be directed to the subscribe link.







  6. The Natural Medicines Comprehensive Database


  8. Oncology Dietetic Group, Academy of Nutrition and Dietetics

This information is for survivors after treatment or on maintenance. Nutrition is meant only to support you. Always talk to your doctor before making any changes.

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