Is Soy Safe?
A quick search on ‘soy & health’ brings up so many conflicting opinions that it can be hard to know what to believe. Does soy protect you from cancer? Can soy cause cancer? Is it safe for men? Is it safe before menopause? Should you avoid it if you’ve already had cancer? A lot of us avoid soy altogether because of these uncertainties, but writing it off completely may mean you miss out on some wonderful benefits! So let’s look at what we really know.
What Does Soy Actually Do To My Body?
Soy contains isoflavones, which are phytoestrogens (meaning they’re a type of plant estrogen). These phytoestrogens act similarly to our own body’s estrogen but they have a much weaker effect. Because of this weaker effect, soy can have either an estrogenic effect (meaning soy can increase estrogen activity in the body), or an anti-estrogenic effect (meaning soy can reduce the impact of too much estrogen).
So how is it possible that soy can both increase AND decrease estrogen in the body!? It seems that this is due to how soy isoflavones bind to estrogen receptors, as well as your body’s overall estrogen levels. When soy isoflavones bind to estrogen receptors they either causes a weak estrogenic effect (increasing estrogen activity in the body), or protect estrogen receptors from binding to stronger acting estrogen (thereby lowering the effect of estrogen on the body).
Here’s a quick example to help put this all together. Let’s compare how estrogen impacts a woman who is premenopausal and a woman who is postmenopausal:
Premenopausal women have higher levels of circulating estrogen (when compared to postmenopausal women). When estrogen levels are higher, soy’s ability to bind to estrogen receptors helps to reduce the damage that high circulating levels of estrogen can have on the body.
Postmenopausal women often see symptoms and changes to their health as a result of the significantly lowered levels of estrogen they now have. In the context of less circulating estrogen, soy binds to estrogen receptors and helps to gently elevate estrogen activity and balance estrogen levels.
What About Men?
Men often avoid soy because they worry it might be feminizing or reduce their testosterone. However, men don’t need to worry about this! Studies have not shown any indication that soy impacts testosterone levels in men, or production of testosterone. A review study found that even intake of up to 240 grams of soy isoflavones daily didn’t affect free or total testosterone levels. In fact, soy is actually recommended as part of a balanced diet in men as it’s been shown to significantly lower the risk of developing prostate cancer later in life.
So Should We All be Eating Soy?
Soy has been shown to either benefit health conditions or act neutrally making it a very safe part of your daily diet. However, there are a few instances when I tell my patients to avoid soy.
Avoid soy if:
You have an allergy to soy (this is more common than you might expect)
You have a histamine intolerance, as assessed by your doctor
You have hypothyroidism and are on medication
When Should I consider Adding Soy to My Diet?
Soy foods have been strongly associated with a reduced risk of breast, prostate, and other hormone-sensitive cancers, as well as lung cancer (in both nonsmokers and smokers alike). This makes soy a great consideration when we are talking about preventative medicine!
I often talk to my patients about adding soy to their diet in any of the following situations:
Women
You are a premenstrual female: It seems that soy intake before menarche has a protective effect later in life, helping to reduce the risk of ER+/PR+ Her2- breast cancers.
You have a higher risk of endometrial cancer or endometriosis: Isoflavones may be protective against endometrial cancer (in pre and postmenopausal women) and endometriosis.
You have a strong family history of breast cancer: While the most significant benefit when it comes to protecting yourself against breast cancer comes from early consumption of soy, regular soy intake over years has shown to be mildly protective against breast cancer in general. If you have a higher risk (aka. you are a ‘previvour’) including healthy forms of soy in diet your can be considered.
You have been diagnosed with breast cancer, and:
Are undergoing treatment: Soy can be helpful for reducing side-effects of treatment, however this is a conversation you should have with your Naturopathic Doctor first.
Are in remission: Soy food intake after diagnosis has been associated with reduced mortality and recurrence in both ER-and ER+ breast cancer patients (pre and postmenopausal). Soy food intake after diagnosis was associated with reduced mortality and recurrence. *ARE YOU SURE IT’S SAFE? Yes, findings of a cohort study were consistent with previous research showing that soy consumption does not adversely affect breast cancer survival.
Are taking Tamoxifen: Consuming soy foods with Tamoxifen has been controversial but recent evidence indicates a high degree of synergy! Because soy can improve Tamoxifen’s protective benefits, anyone on this drug can and should eat soy foods freely.
Are taking Anastrozole / Letrozole: Similar to Tamoxifen, soy has been found to lower the risk of recurrence when consumed alongside aromatase inhibitors. In patients on Anastrozole, it’s been found that those with the highest intake of isoflavones had an 18% lower chance of recurrence than those with the lowest consumption.
You are going through menopause: Soy helps reduce hot flashes, improves vaginal dryness, and improves cognitive function. However, it takes about 8-12 weeks to see benefit, and unlike the other research, in menopause it seems a supplement form of soy (genistein) may be a better option.
You have been diagnosed with PCOS: Legumes (including non-GMO, organic soy) are rich in inositol, which helps to control blood sugar levels and can support ovulation.
Men
You have a strong family history of prostate cancer: Soy has been found to be the most important dietary protectant against prostate cancer (due to it’s genestein content). Genestein competitively blocks hormones at their receptor sites in the prostate, helping to inhibit the growth of prostate cancer cells.
You are currently undergoing radiation for prostate cancer: Research has shown in that in men being treated for localized prostate cancer with radiation, consuming soy isoflavones at the same time as treatment resulted in significantly less bowel and sexual adverse effects.
You have a history of prostate cancer: Soy intake has had mixed outcomes here but has been shown to either reduce the risk of recurrence or have no impact. For this reason I often suggest my patients consider including soy as it won’t be harmful, and it may be protective.
How Do I know What Soy Products to Buy?
I don’t often prescribe soy capsules, but instead opt for dietary sources of soy. Not only is soy a complex plant protein (meaning it works best when we don’t interfere with it), the most compelling research has been done on soy as a food source. Additionally, aside from the phytoestrogenic effect, soy is a complete protein and is rich in nutrients like fiber, b vitamins, potassium, and magnesium.
That being said, choose soy wisely. More than 90% of the soy produced in the US is genetically modified, and since we don’t have enough data to show that GMO foods are safe, I tell my patients to avoid GMO foods as much as possible. Additionally, most genetically modified soy is treated with the pesticide glyphosate, which is controversial and proving to cause a lot of damage to our health long-term. So try as much as you can to choose organic soy products and choose soy that has been as unmodified as possible → consider: tempeh, miso, and edamame.
Next Steps
Want more support? Choosing herbs, supplements, and more targeted treatments needs to done be done on an individual basis, taking into consideration your whole health history. I want your treatments to not only be safe but to have as many positive effects on your health as possible. Naturopathic medicine is not about over-complicating your life, but empowering you so you can make smart, safe choices that you feel good about.
Ready to make a change?
Sorting through the complicated and ever-changing landscape of health news can be daunting. When it comes to your health, it’s important to be your own advocate AND have a doctor that will advocate for you. If you are in search of more direct and personalized ways to care for your health don’t be afraid to reach out and ask. I can help.
In support of your health,
Dr. Hayhlee Clarence, ND
References (see hyperlinks above)