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10 reasons why breast cancer thrivers should enjoy soy

Updated: Sep 8, 2020

Let's take the 'oy' out of soy and breast cancer risk. Here are 10 reasons anyone diagnosed or at risk of breast cancer can safely enjoy soyfoods. Yes, this means for both men and women.

The soybean, a legume from China, is now grown in the U.S. and other countries. Processed soybeans can be found in such products as soy milk, soy powder, soy protein concentrate, and isolated soy protein products.

Soyfoods are a source of high-quality protein, calcium, iron, and essential fatty acids. They also offer lignans, which are protective for breast cancer. In fact, women who eat several servings of soy daily have the same iron levels as women who eat meat.

Soy contains phytoestrogens (plant estrogens) called isoflavones. These compounds can also be found in other foods, such as flaxseeds, but soy is the primary source of isoflavones. This class of compounds may be structurally similar to estrogen, but they do not act the same as the estrogen hormone in the body.

This article focuses on dietary portions of foods like tofu, edamame, and soy milk. Safety has not been established above normal dietary portions, usually found in soy protein powders and supplements.

For specifics on the types of soyfoods to keep in or avoid, see my previous post, Is soy helpful or harmful for cancer survivors?

Tofu and cucumber salad
Tofu and cucumber salad

Soy is safe

A quarter century of research shows soy to be safe for those diagnosed or at risk for all types of breast cancer, whether cancers are fueled by hormones or not, or caused by genetic mutations, such as BRCA1 or BRCA2. Population-wide and consistent research by The American Institute for Cancer Research, "indicate no increased risk for breast cancer survivors who consume soyfoods."

Who else considers soy to be safe? The American Cancer Society, American Institute for Cancer Research, Canadian Cancer Society, World Cancer Research Fund International, and the vegetarian and oncology dietetic groups of the Academy of Nutrition and Dietetics.

Soy is different from the hormone estrogen as the isoflavones in soy bind to only one receptor in the breast, rendering it relatively harmless. The actual estrogen hormone binds to two receptors and can influence tumor growth in those who are susceptible.

As for the myth that men grow breasts from soy, this was based on one unusual case, when one man drank three quarts (12 cups!) of soy milk every day. He developed gynecomastia, or enlarged benign breast tissue. It was completely resolved when he discontinued his soy habit.

Soy may be protective for breast cancer

But timing is everything. Fewer breast cancers are seen in women who eat high amounts of soy during childhood and adolescence, rather than women who start older, according to the Natural Medicines Database. Adolescence is when breast tissue develops, and new research shows this time may set the stage for breast cancer growth later on in life.

As little as a serving a day is linked to a 25-50% lifetime reduced risk of breast cancer in adolescents. So it's a good idea to introduce your daughters to soyfoods early on.

Ethnicity may play a part here too. Breast cancer is 14% to 26% lower for women with a high soy diet compared to those with a low soy diet, particularly in Asian and Asian-American women (although that effect diminishes after migration to the US, possibly due to eating less soy.) In Asia, intake of isoflavones is 30-50 mg daily, while Americans eat less than 3 mg a day. The lower intake may be because processing soyfoods can reduce isoflavones by as much as 80%, such as in meat replacements. Higher amounts of isoflavones are found in tofu and fermented foods such as tempeh and miso.

Women who eat soy have reduced breast cancer recurrence and improved survival

Studies of 11,000 women in the U.S. and China show a statistically significant rate of reduced recurrence and better survival a year after a breast cancer diagnosis. In 6,200 American and Canadian women with breast cancer, those women who ate higher amounts of isoflavones had a 21% lower risk of having died.

Soyfoods may help boost the effectiveness of the medications many women are prescribed to reduce recurrence. Longer survival is specifically seen with medications such as Tamoxifen and the aromatase inhibitor, Anastrozole.

Soy may be the key to interfering with estrogen receptors, but was even seen to protect both ER- and ER+ breast cancer. In one study, it was more protective even for postmenopausal women with the BRCA1 and BRCA2 mutations compared to a placebo group. However, soyfoods should never be considered similar to the effectiveness of estrogen blocking or reducing medications, which have an 80% success rate in reducing recurrence.

Soyfoods may help with menopausal symptoms

The symptoms associated with sudden menopause in women who undergo surgery or medications for breast cancer, are more persistent and severe than gradual menopause. Soy has been studied for its effect on hot flashes in 50 clinical trials, and in a meta-analysis, isoflavone supplements did reduce the number and severity of hot flashes by half. It may take two months to see an effect. Other studies showed no effect with supplements. However, anecdotally, I haven't seen any effect on my patients in alleviating symptoms. This could be due to not getting the same amount of isoflavones as found in the supplements studied.

Currently, 100 mg a day of isoflavones are considered safe, but the recommended portions are 2-3 servings of soyfoods a day, such as:

  • 1/2 cup cooked edamame, and 1/2 cup silken tofu

  • Or, an 8 ounce cup of soymilk, 3 ounces of soy chicken, and 1/2 cup tempeh.

Talk to your medical team before taking any supplements.

Soy is linked to better bone health

Women with the BRCA1 and BRCA2 mutation who have their ovaries removed before menopause, are at increased risk for bone loss. Soy allows bone to absorb more calcium. Soy protein is an easy and healthy way to strengthen bone density. Soy is also linked to fewer fractures in early postmenopausal women. Eat up your edamame!

Lifestyle changes such as adding plant foods help reduce breast cancer risk

A plant-forward diet, where the majority of the plate is filled with plant foods rather than animal protein, is strongly recommended for breast cancer survivors by numerous cancer organizations. Soy-based foods such as tofu, tempeh, edamame, and miso, are flavorful and creative culinary additions to a survivor plate.

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Sauteed tofu
Sauteed tofu

Soy protein lowers cholesterol and improves heart health

Fermented soy may have the edge here: Eating fermented soy such as tempeh leads to a reduced risk of dying from cardiovascular disease. Postmenopausal women who eat more soy have a lower risk of stroke too.

It's especially helpful to replace meat with soy, as this lowers cholesterol and reduces saturated fat in the diet. Although the FDA has said research is inconsistent, it nonetheless found that soy protein reduces cholesterol by a statistically significant 3-4%. Soy protein also improves the health of our arteries.

Soybeans improve gut health

One word: fiber. Fiber boosts gut health. Eating foods high in fiber increases the variety of good bugs in the gut microbiome—making for a stronger immune system too. Tofu is low in fiber, but try edamame (8 grams of fiber per cup) or tempeh, with 9 grams in every half-cup.

Soy helps reduce the risk of other cancers

The fiber in soy has the potential to decrease the risk of colorectal cancer, and by strengthening the gut microbiome, other cancers as well. Foods with isoflavones are linked to a decreased risk of lung and prostate cancer.

Soy may reduce wrinkles

I saved the best for last.

I don't have anything against wrinkles, but as it is a concern for many women, here's some good news. Women who ate 40 mg a day of soy isoflavones (less than a 1/2 cup of cooked soybeans) showed better skin elasticity and fewer fine wrinkles compared to a group given a placebo.

To put your soyfoods into action, here's a recipe for Tangy Peanut Glazed Tempeh with Broccoli.

With thanks to the Vegetarian Nutrition Dietetic Practice Group of the Academy of Nutrition and Dietetics for their plant-based resources for professionals.



Tangy Peanut Glazed Tempeh with Broccoli

Tempeh is a cultured protein made of fermented, cooked soybeans. It's a high protein meat alternative, and absorbs the flavor of this tangy peanut sauce. Cooking reduces the benefits of the live bacteria, but no matter. Tempeh is not only delicious, it offers 17 grams of protein in every half-cup.

Mix up the types of vegetables you use depending on what's available. We have used broccoli and peppers, cauliflower and carrots, green beans, etc. It's all delicious with this peanut glaze.

You can also vary the cut of the tempehstrips, cubes, or triangles.

tempeh skewers
Skewered Tempeh

Tangy Peanut Glazed Tempeh with Broccoli.
Tangy Peanut Glazed Tempeh with Broccoli.
recipe for tempeh and peanut glaze
recipe directions

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

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