This article presents a series of studies showing that soy intake does not increase breast cancer risk. In contrast, the opposite is true. Soy intake lowers the risk of breast cancer.
Breast cancer is currently the most common cancer globally, accounting for 12.5% of all new annual cancer cases worldwide. It is the second most common cancer in the US, per the CDC.
The concern that soybeans may increase breast cancer risk arose when mice studies showed that the estrogen-like properties of isoflavones increase breast cancer risk.
Studies in mice by (Allred et al. (2001) and (Ju et al. (2006) with no thymus and ovaries and implanted with estrogen-sensitive breast cancer cells showed that isoflavones could stimulate the growth of existing tumors.
Isoflavones are substances in soybeans that have an estrogen-like property—being plant versions of estrogen, and they are structurally different and significantly weaker than human estrogen.
Still, having estrogen-like properties, isoflavones can alleviate menopausal symptoms like flushing due to a decrease in endogenous estrogen. They are also helpful in preventing osteoporosis.
Breast Cancer Hormone Receptors
Before we go to the human studies about soy intake and breast cancer, I will briefly present the different types of breast cancers based on their hormonal receptor status.
Estrogen and progesterone are hormones that could affect the growth of breast cancers that have receptors for them. The receptor status directs the treatment.
Hormone receptor-positive cancers tend to grow more slowly than hormone receptor-negative ones. For example, estrogen receptor-positive tumors (ER+) are treated with estrogen blockers like tamoxifen.
ER+ breast cancers in postmenopausal women can benefit from medicines that stop the body from producing estrogen, like anastrozole.
Hormone receptor-negative breast cancers have no estrogen or progesterone receptors (PR-). Treatment with hormone therapy drugs is not helpful for these cancers.
These cancers tend to grow faster than hormone receptor-positive cancers. Hormone receptor-negative cancers are more common in pre-menopausal women.[1]
Triple-negative breast cancer cells don’t have estrogen or progesterone receptors and also don’t make any or too much of the protein called HER2.
Triple-negative breast cancers grow and spread faster than most other types of breast cancer. And because they don’t have hormone receptors and HER2 proteins, hormone therapy and medicines that target HER2 aren’t helpful, either. But chemotherapy can still be beneficial.[4]
With that, let’s go to the studies.
Shu et al. (2009) studied 5,042 women aged 20 to 75 diagnosed with breast cancer that was followed for three years. Outcome measures were total mortality and breast cancer recurrence or breast cancer-related deaths.
They found that soy food consumption was significantly associated with decreased risk of death and recurrence.
Guha et al. (2009) examined the role of soy isoflavone intake and the risk of breast cancer recurrence by hormone receptor status, menopausal status, and tamoxifen therapy in a cohort of 1,954 female breast cancer survivors. They were followed for 6.31 years.
They found a reduced risk of cancer recurrence in postmenopausal women with a higher intake of soy isoflavones than with no intake.
In postmenopausal women treated with tamoxifen, there was an approximately 60% reduction in breast cancer recurrence in those with the highest soy intake.
Soy isoflavones consumed at levels comparable to those in Asian populations may reduce the risk of cancer recurrence in women receiving tamoxifen therapy and appears not to interfere with tamoxifen efficacy.
Caan (2011). followed 3,088 breast cancer survivors for 7.3 years. They used data from two studies in the US and one from China. They conclude that soy foods have no adverse effects on breast cancer prognosis.
Chi et al. (2013) examined five studies that included 11,206 patients. They found that soy intake after breast cancer diagnosis reduced mortality and recurrence.
Subgroup analysis showed that soy intake might be associated with lower mortality in breast cancer patients regardless of estrogen receptor and menopausal status.
Nechuta et al. (2012) analyzed 9,514 breast cancer survivors diagnosed with invasive breast cancer from two US cohorts and one Chinese cohort. Follow-up was 7.4 years.
Despite large differences in soy isoflavone intake by country, isoflavone consumption was inversely associated with recurrence among US and Chinese women, regardless of whether data were analyzed separately by country or combined.
In women with ER+ tumors, tamoxifen users with higher isoflavone intake had a reduced risk of breast cancer recurrence compared with women who did not use tamoxifen and consumed the lowest amount of isoflavones.
Kang et al. (2013) studied 524 patients with breast cancer who were receiving adjuvant chemotherapy and followed them for 5.1 years.
High dietary intake of soy isoflavones was associated with a lower risk of recurrence among postmenopausal patients with breast cancer positive for estrogen and progesterone receptors and those receiving anastrozole as endocrine therapy.
Chen et al. (2014) conducted a meta-analysis of 35 studies that reported results of the association between soy isoflavone intake and breast cancer risk for pre-and postmenopausal women.
Soy isoflavones intake protects against breast cancer for pre-and postmenopausal women in Asian countries.
For pre- or postmenopausal women in Western countries, there is no association between soy isoflavone intake and breast cancer.
Baglia et al. (2016) measured soy food intake in adolescents and adults via a food questionnaire in 70,578 Chinese women aged 40-70. They were followed for about 13.2 years.
High soy intake during adulthood and adolescence was associated with reduced pre-menopausal breast cancer risk. In contrast, soy intake in adulthood was associated with postmenopausal breast cancer only when adolescent intake was low.
In summary, the intake of foods containing soybeans does not increase the risk of breast cancer in women. This knowledge is essential because the next article’s subject is the health benefits of soy and nattokinase.
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References:
- American Cancer society. Breast Cancer Hormone Receptor Status
- Allred CD, Allred KF, Ju YH, Virant SM, Helferich WG. Soy diets containing varying amounts of genistein stimulate growth of estrogen-dependent (MCF-7) tumors in a dose-dependent manner. Cancer Res. 2001 Jul 1;61(13):5045-50. PMID: 11431339.
Related:
- High-Dose Nattokinase to Shrink Atherosclerosis and Lower Blood Lipids
- Nattokinase is Nontoxic with a High Safety Margin
- The Outstanding Vascular Effects and Dose of Nattokinase
- Nattokinase Degrades the SARS-CoV-2 Spike Protein
- Another Study shows Nattokinase can Destroy the S1 Spike Protein
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Soy for women… no problem, hormones decline with age, so boosting them back to a younger/natural state should be fine.
Soy for men… I’d personally avoid that. All bioidentical hormones used today (Estriol, Estrone, Estradiol, Progesterone, Testosterone) are manufactured from soy.
Yes– soy is weak… but there is a balance (Metabolization between/ aka “The Dance of the Hormones”) and I was taught by an old school pharmacist that healthy folks should be very cautious about blindly upsetting that. I think you can see that today in men who have been feminized by consumption/exposure to estrogenic substances (including environmental plastics).
Excess estrogen in males is a valid concern. Estrogen disruptors are also found in many plastics, canned foods, and beverages and seem almost unavoidable. To get the effects of soy, nattokinase can be a good alternative for its cardioprotective and neuroprotective effects.