Soy Reduces Breast Cancer Risk


Confused about soy?  The research on its benefits continues to pile up, including studies on women. A 2016 review of each of the major research areas involving soy concludes that it reduces the risk of breast cancer in women and has the following beneficial characteristics.

10 Benefits of Soy

  1. It has a high protein content compared to other plant proteins, and is a good substitute for animal protein. The protein in soy is easily digested. Replacing your animal protein with soy, legumes, mushrooms and hemp seeds will have the added benefit of decreasing greenhouse gases responsible for climate change.
  2. The low carbohydrate content of soybeans means that it is good for people with diabetes. It has a low glycemic index and will not elevate insulin. High insulin levels otherwise increase breast cancer risk threefold.
  3. Soy is a good source of the minerals potassium, calcium and iron. The absorption of calcium in soymilk is similar to what one would obtain from an equivalent amount of cow’s milk. Thus it is a good replacement for dairy, and source of iron for vegetarians.
  4. Soy contains isoflavones, such as genistein, which act as weak estrogens that offer protection against breast cancer and selectively bind to certain estrogen receptors to block the body’s stronger estrogens. Isoflavone intake among adults ranges from about 30–50 mg/day in Japan but is less than 3 mg/day in the United States, Canada and Europe. Japan’s breast cancer incidence is about half of that in the US and Europe. Chinese women, who consume a diet higher in isoflavones than western women, have approximately one fifth the breast cancer rate as American women.
  5. Soy protein significantly lowers LDL-cholesterol by approximately 4% to 6%, when about 25 grams a day are ingested. It also lowers circulating triglyceride levels (~5%) and raises beneficial high-density-lipoprotein (HDL)-cholesterol levels (~1%–3%), thereby reducing the risk of cardiovascular disease.
  6. Soy intake helps to lower blood pressure by 1.5-2.5 mmHg and helps to reduce stiffness in the walls of the arteries, also reducing the possibility of cardiovascular disease.
  7. The high-quality protein and well-absorbed calcium provided by many soy foods can contribute to bone health and reduce the risk of osteoporosis.
  8. Higher soy intake early in life is associated with a 25% to 60% reduction in risk of breast cancer later in life. The protection afforded by isoflavones may be similar to the observed protective effect of early pregnancy against breast cancer.
  9. In a meta-analysis of five prospective studies, two from the United States and three from China, involving over 11,000 women with breast cancer, it was found that soy consumption after a diagnosis of breast cancer was associated with significant reductions in breast cancer recurrence and mortality. Soy consumption was similarly beneficial in Asian and non-Asian women.
  10. Higher soy consumption is associated with as much as a 50% reduction in prostate cancer risk.

Soy Intake Reduces the Risk of Breast Cancer Recurrence

A study done in China (published in the Dec. 9, 2009 Journal of the American Medical Association) examined the safety of soy food consumption among 5,042 breast cancer survivors, aged 20 to 75. Women were recruited into the study six months after a breast cancer diagnosis. After four years, women with the highest intake of soy protein had a 29 per cent lower risk of death and were 32 per cent less likely to have a breast cancer recurrence compared with women with the lowest intake. Soy was protective for women with either early or late stage breast cancer and in women with estrogen-receptor (ER) positive and ER negative breast cancer.

Soy intake actually enhanced the effectiveness of the drug, tamoxifen. In fact, women who consumed the most soy and did not take tamoxifen had a lower risk of cancer recurrence and death than tamoxifen users with low soy intakes. In effect, soy food intake performed better than tamoxifen in preventing recurrence! The women who consumed the most soy, whether they used tamoxifen or not, had a 35% reduction in recurrence.

A second study called the Life After Cancer Epidemiology (LACE) study, published in November 2009, followed 1,954 northern California early stage breast cancer survivors for six years and found that postmenopausal women with a high soy intake – compared with none – had a lower risk of their cancer returning. Among postmenopausal women treated with tamoxifen, those who consumed the most soy were 60 per cent less likely to have their breast cancer recur compared with women with the lowest intakes.

In studies on rats, soy inhibits the growth of human-derived breast cancer tumors in a dose-dependent manner and causes cell death (apoptosis) in breast cancer cells.

Soy in Adolescence is Protective

When consumed in childhood, soy substantially decreases the risk of premenopausal breast cancer. Women who consume a high amount of soy foods consistently during adolescence and adulthood (i.e. at least one serving of tofu a day) have a substantially reduced risk of premenopausal breast cancer.

Less or no significant association with soy food consumption is found for postmenopausal breast cancer.

Soy Isoflavones

Genistein (from soy), an isoflavone, in combination with capsaicin (from cayenne) exerts anti-inflammatory and anticarcinogenic properties that protect from breast cancer.

When postmenopausal women consumed 20 g of soy protein containing 160 mg of total isoflavones daily, there was a significant improvement in a variety of menopausal symptoms (vasomotor, psychosexual, physical, and sexual) among the women taking isoflavones, while no changes were seen in the placebo group.

However, we recommend you DO NOT take isolated isoflavones – the greatest and safest benefit from soy is from the whole food.

Fermented vs Unfermented

Some people assert that only fermented soy should be consumed, such as tempeh or miso. Fermented soy can be easier to digest, but the above studies did not differentiate between fermented or unfermented – they both work. Fermented soy will be a problem for women dealing with Candida overgrowth, which is not uncommon.
It is best if your soy foods are not overly processed, so my recommendation is to use organic edamame, tofu, miso, tempeh and soy milk as your primary sources of soy isoflavones.

Caution if Allergic

A note of caution though – some people have allergies to soy, with symptoms of gas and bloating. If you are one of them, then minimize or avoid soy and use 2-4 tbsp. daily of freshly ground flaxseed instead.

Soy and Thyroid Function

Soy can interfere with the thyroid gland’s ability to utilize iodine – so always have a dietary source of iodine, hence the daily need for sea vegetables.
The combination of seaweed plus soy improves the ratio of 2-OHE:16alpha-hydroxyestrone (16alphaOHE(1)) to help decrease breast cancer risk. Ask your health care practitioner to monitor your TSH levels to make sure thyroid function is maintained.

Use Organic Soy

And finally, eat organic soy. The pesticides used in growing soy beans have caused breast cancer in animal studies.

How Much Do You Need?

So how much do you need? A daily intake of 11 grams of soy protein offered the most benefit, an amount found in about 11/2 cups of soy milk, one soy burger, 1/2 cup of edamame (young green soy beans) or 1/2 cup of firm tofu. Higher intakes did not offer extra protection against breast cancer, although 25 grams daily is required to lower LDL cholesterol.

This chart can help you determine your soy intake.

Food Protein Content (Grams) Quantity Required
Miso 5.9 ½ cup
Tofu, silken 8.1 ½ cup
Tofu, firm 15.6 ½ cup
Soybeans, boiled 16.6 ½ cup
Soybeans, dry-roasted 39.6 ½ cup
Soy milk 5.6 1 cup
Tempeh 19.0 ½ cup
Soy protein powder 58.1 1 ounce

All-in-all, organic soy is a powerful dietary ally in reducing the risk and recurrence of breast cancer.


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