There is a lot of confusion surrounding soy and hormone health. On the one hand, many love soy for its claims of taming hot flashes, and protecting against hormonally-driven cancers. But, some people believe that soy foods can increase estrogen levels in men, while others claim that the soy and testosterone myth is just that—a myth. Let's explore the real effects of soy on hormone levels for both men and women, and what this means for health. Could there be any truth to its claims to reduce cancer risk, or should you avoid high soy consumption? And, if you're going to eat soy foods, which ones are better?

In our modern food system, soy is in the vast majority processed foods. Baby formula, protein bars, sweets, and most shelf-stable condiments now contain soy. But as it becomes an increasingly popular ingredient, some are concerned that its use may pose a problem for reproductive hormones. Soy, as well as some other plant foods, contain phytoestrogens, which are naturally-occurring compounds that have the ability to bind with our hormone receptors the same way human estrogen does.

Traditionally, foods like miso or tofu have been a staple in Eastern diets, providing a high-quality, non-animal source of accessible protein. Today, we use soy protein, soy flour, soybean oil, and other derivatives.

Learn more about conditions we treat: Hormonal Imbalance

How much does soy mess with your hormones?

First, research suggests that soy has a mostly neutral or slightly beneficial effect for overall health, whether we’re talking about hormones, menopause, cardiovascular function, or anything else. Phytoestrogens may indeed bind to estrogen receptors in both men or women, but they have much weaker effects than true human estrogen. This may actually be beneficial in some cases.

Soy does not increase estrogen or lower testosterone levels in men

Soy foods do not appear to increase estrogen or lower testosterone in men or women. In 2010, a meta-analysis published in Fertility and Sterility shared the results of more than 30 studies involving hundreds of men. This same analysis was updated in 2020 in the Journal of Reproductive Toxicology for a total of 41 studies reviewed.

In both meta-analyses, the researchers concluded that “neither soy foods nor isoflavone supplements alter measures of bioavailable T concentrations in men” (1).

A 2019 meta-analysis also found that soy supplements had no effect on thyroid hormones in both adult men and women, though some suggest it may interfere with thyroid medication (2).

If you’re having issues with low testosterone, chances are there are bigger issues at play than soy intake, such as:

Diet high in processed foods and refined carbohydrates
Insulin resistance or blood sugar imbalance
Stress
Poor sleep
High body fat percentage

The combination of a poor diet and a sedentary lifestyle can quickly become trouble for men's testosterone levels.

Read: Low Testosterone: Is TRT Right for Me?

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Soy isoflavones may offer some benefit

Isoflavones are a type of polyphenol found in legumes, including soybeans, chickpeas, fava beans, pistachios, peanuts, and other fruits and nuts. Isoflavones exhibit antioxidant, anticancer, antimicrobial, and anti-inflammatory properties (3).

Daidzein and genistein are the most common isoflavones, whose chemical structure does look similar to that of estrogens. Isoflavones, however, elicit either a weak estrogenic or anti-estrogenic effect, depending on the levels of internal estrogens already present in the body (3).

Soy isoflavones combat the “bad” type of estrogen

Soy isoflavones potentially block the binding of more potent estrogens, potentially playing a role in preventing hormone-related cancer like breast cancer, cervical cancer, and prostate cancer or testicular cancer in men (4). This is especially true for post-menopausal women as the ovaries cease estrogen production.

Interestingly, the incidence of breast and prostate cancers is lower among Asians in comparison to people in the Western world. This could be related to the significantly different consumption of soy foods and soy isoflavones in Asian diets (50 mg/day) compared with Western diets (1-3 mg/day) (5).

Shop: Support for healthy estrogen metabolism.

Not all soy is ‘equol’

When soy phytoestrogens are broken down by certain bacteria in the microbiome, they make a compound called equol. If your gut bacteria produce equol, your body is more likely to reap the health benefits of soy phytoestrogens. Notably, women who had more equol in their urine also had lower levels of estradiol in their blood (6).

However, only about 30-50% of people have the right bacteria present in their microbiome to produce equol. It’s found more often in the microbiome of those who live in Eastern regions where soy foods are eaten more often. One study found suppressed estradiol levels following increased soy intake, but only in women of Asian descent (7).

So, does that potentially mean there’s zero benefit to eating soy if your gut bacteria can’t produce the beneficial compounds?

That’s where soy supplements come in, as they’re paired with a form of this compound. Researchers are still working to fully understand its effectiveness and bioavailability, but some studies do support its use to treat common symptoms of menopause, such as hot flashes (8,9).

The health effects of soy isoflavones

Eating soy may lower “bad” estrogens in men and women. Isoflavones bind to receptor sites, and function as weaker, less potent estrogens.
Soy phytoestrogen supplementation may protect against breast and other cancers. High-dose supplementation may reduce tumor activity in estrogen-dependent cancers, though further research is needed (10).
Soybean oil may actually help support testosterone production in men. One study found that consumption of soybean oil activates steroid synthesis in Leydig cells, which are specialized cells located in the testicles responsible for producing testosterone (11).
Some research suggests soy isoflavones can decrease the risk of developing prostate cancer (4).

In addition, soy phytoestrogens may be somewhat protective against coronary heart disease. Soy foods are a good source of B vitamins, essential amino acids, and non-heme iron.

Missing out on vital nutrients? Nutrition Supplement Guide: Dosages, Recommendations, and Facts.

Soy formula may impact gut health in infants

Nearly a third of infant formula on the market today is soy-based, and some parents worry that the estrogenic activity in soy could be an issue for both neurobiological development and gut dysbiosis in babies. Troublingly, there may be some truth to this.

In 2019, a review showed evidence that phytoestrogens may have a detrimental effect on babies who are exposed to soy at a young age. The review found a possible correlation between soy phytoestrogen intake and aggression and anxiety later in life (12).

Soy foods may also alter gut bacteria, and this phytoestrogen-induced change in gut bacteria might be another way in which exposure to such compounds lead to later neurobehavioral disruptions.

Healthy ways to consume soy foods

Soy may not be the controversial feminizer of men that it’s made out to be, but that doesn’t mean it gets a green light across the board, either.

More than 90% of soy in the U.S. and globally is genetically modified, making it an issue for both biodiversity in the ecosystem, and exposure to microbiome-disrupting pesticides like glyphosate (13). While most soy is grown for animal food, being particular with your choice of soy products may indeed be more impactful to your health than eating soy foods in the first place. The best types of soy products to consume are:

Fermented soy foods such as:

Natto
Miso
Tempeh

Or, organic and non-GMO soy foods like:

Tofu
Edamame

If you’re trying to reduce pesticide exposure in your diet, be aware of soy and soy products as a possible source.

Soy benefits and risks

Soy is a hot topic in the health world, with people on both sides of the fence claiming it’s either great or terrible for your health. The reality is that soy doesn’t seem to affect reproductive hormones in men or women, but it may not be a good idea for everyone. Soy foods aren’t bad for you, but many people lack the necessary gut bacteria to reap the health benefits of soy phytoestrogens. Soy foods can be a good source of protein and nutrients, so choose organic or non-GMO products whenever available.

Resources

https://www.sciencedirect.com/science/article/pii/S0890623820302926
https://www.nature.com/articles/s41598-019-40647-x
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4924202/
Phetnoo, N., Werawatganon, D., & Siriviriyakul, P. (2013). Genistein could have a therapeutic potential for gastrointestinal diseases. Thai J Gastroenterol, 14, 120-5.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4129534/
https://www.nature.com/articles/s41598-021-98872-2
https://pubmed.ncbi.nlm.nih.gov/10839307/
https://pubs.acs.org/doi/10.1021/jf400097m
https://pubmed.ncbi.nlm.nih.gov/20080366/
https://pubmed.ncbi.nlm.nih.gov/23274118/
https://nutritionandmetabolism.biomedcentral.com/articles/10.1186/s12986-021-00580-1
https://www.frontiersin.org/articles/10.3389/fnut.2019.00142/full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8009591/

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the author

CentreSpring MD, formerly known as Atlanta Center for Holistic and Integrative Medicine, provides the best medical care by using an integrative approach to find a patient’s centre—their core—empowering them to spring forth into health.

Blog Reviewed By:

Dr. Taz Bhatia, M.D.

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The Truth About Soy and Hormones