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Soy Bad for Men: Truth About Soy Products – Farr Institute

Is Soy Bad for Men: The Truth About Soy Products and Testosterone

Soy food products are rumored to wreak havoc on men’s hormone levels, and in extreme cases, cause hot flashes and the dreaded man breasts. 

Well, we have the science-backed evidence that gives the true answer on whether the effects of soy consumption are good or bad for men’s health.

In this article, we detail what soy is, explain the effects of this protein-packed legume on testosterone, and finally break down the one ingredient that started this false rumor in the first place. 

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Key Takeaways: Does Soy Affect Men?

  • Soy does not turn men into women, cause infertility, prostate cancer, man-boobs, or affect reproductive hormones.
  • Similar to whey protein, soy may increase energy and improve recovery time during resistance exercise training and other athletic workouts.
  • Isoflavone is a phytoestrogen compound found in soybeans with estrogen-like effects, but these effects are much weaker than estrogen found naturally in the body. 
  • Isolated soy protein supplements like pills and powders are not as healthy as soy foods and should not be taken for an extended period. 
  • A balanced diet containing soy may lower cholesterol, improve blood sugar and blood pressure, protect your heart from disease, and may prevent some men from developing prostate cancer. 

Does Soy Affect Testosterone in Men?

Soy does not negatively affect testosterone in men. There are numerous scientific studies proving that neither soy foods nor soy protein affect hormones in men in any way.

In fact, most studies show that soy consumed in moderation has beneficial effects on men’s health as well as women and children, proving there’s no reason for most people to avoid soy.

The few clinical studies that show soy having a negative effect on hormones were performed on animals, mainly mice and rats. 

But there was one study conducted on humans that resulted in hormonal disturbances. However, the subjects involved consumed an extraordinarily high and unrealistic amount of soy on a nutrient-deficient diet—about nine times the amount consumed by most older men [1].  

There are foods that kill testosterone and likewise, foods that increase testosterone, but soybeans and soy food products are not one of them. Soy does not have a hidden dark side and is not a dangerous food for men.

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How Much Is Too Much Soy?

The Food and Drug Administration recommends eating 25 grams of soy a day for a balanced diet, equal to 2-4 servings per day [2]. Too much of anything, even if it’s healthy, could have adverse side effects and lead to health problems. 

That being said, it’s very difficult to overeat soy. Men in Asian countries, especially Japanese men, consume the most soybeans globally, and some eat anywhere between 60-120 grams of soy per day without any adverse side effects [3]

It would be best if you watched out for highly processed foods containing soy, such as soy protein bars, soy powders, and soy meat substitutes. These tend to have more unnecessary ingredients like sugar and salt, and if consumed in large amounts can lead to negative health effects like cardiovascular disease. 

Soy and Estrogen: How Does It Affect Men?

Soybeans contain a high concentration of a compound called isoflavones, a type of plant estrogen also known as phytoestrogen. This compound can bind to estrogen receptors and mimic estrogen properties found in the human body. However, the impact of isoflavone is much weaker and does not affect estrogen levels [4].   

Fortunately, the effects of plant estrogens on men’s health are very positive. Isoflavones are antioxidant compounds that may prevent some types of cell damage [5]. Incorporating a diet with soy isoflavones may reduce the levels of bad cholesterol and lower blood pressure [6].

The binding effect of isoflavone that mimics estrogen may help improve bone density, improve memory impairment, and reduce hot flashes in older women [7]. This same effect may also block the overproduction of estrogen, lowering your risk of certain cancers, but scientists must perform further research in this area [8].

Can soy reduce the occurrence of hot flashes in menopausal women?

Can soy reduce the occurrence of hot flashes in menopausal women
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Can soy reduce hot flashes in menopausal women
Isoflavone, which is found in soy, can reduce hot flashes in menopausal women

is soy bad for men Effectiveness of isoflavone supplementation at reducing the occurrence of hot flashes in menopausal women

Will Soy Increase Estrogen Levels in Men?

Absolutely not! Testing has shown that eating soy protein and foods containing soy isoflavones does not increase estrogen levels or decrease testosterone levels in men. But there are other ways that men can increase testosterone naturally without worrying about increasing estrogen. 

>>Boost your testosterone with TestoPrime

Where Did the Soy Estrogen Myth Start?

The soy myth has been around since the 1950s when animal studies on soy first began but has subsequently been debunked multiple times since. 

Soy was initially shown to negatively affect male rats and mice, including lowering testosterone, decreasing sperm count, and affecting litter size [9]. A later study tested the effects of soy on 20 men for 83 days, and two of those men reported female-like changes in their bodies once the experiment concluded [10]

But before you toss out your tofu, let’s take a deeper look into these studies. 

First of all, rats and mice are not humans and therefore process food differently. Furthermore, the rats and mice involved in these studies consumed a diet primarily consisting of only soy in extremely high amounts. It would be very difficult for humans to consume the same amount of soy in relation to what scientists provided for the animals in these experiments.

But that didn’t stop some from jumping to the conclusion that if soy intake has a negative impact on lab rats, they surely have similar effects on humans. 

As for the one study that found two men having feminizing of the chest? Again, dosing is an important factor here. Administrators gave these men 18-36 servings of soy each day and in supplement form, not food. 

The soy intake by using isoflavone supplements would be abnormally high for anyone. Other human studies have concluded that soy foods are safe to eat and beneficial to any healthy diet. 

Is Soy Healthy?

Yes. Soybeans are a high-protein, plant-based food containing all nine essential amino acids and packed with nutrients like fiber, iron, vitamins, minerals, and antioxidants [11]

Health Benefits of Soy

6 health benefits of soy:

Is Soy Bad for Men

  1. Promotes heart health
  2. Lowers cholesterol
  3. High in iron
  4. Reduces high blood pressure
  5. Lowers blood sugar
  6. May reduce the risk of some cancers

There are many health benefits of soybeans and soy protein when included in a balanced diet. Medical doctors and health professionals have found that plant proteins like soy help improve multiple chronic conditions.    

Promotes Heart Health

Only 10%-15% of fat from soy is saturated fat, lowering your risk of heart disease. Soybeans also include omega 6, omega 3, and polyunsaturated fats, which help lower cholesterol, all necessary for a healthy heart [12].

The isoflavone in soy may reduce inflammation of blood vessels which is beneficial to cardiovascular health [13].

Lowers Cholesterol

Soy isoflavone may reduce LDL, the bad cholesterol by 3% – 6%, which doesn’t sound like much, but every little bit helps when it comes to improving your lifestyle [14]

Soybeans have about 10g of fiber per cup, which can help lower cholesterol in other foods [14]. It also contains less saturated fats than meats like beef and pork, which are essential to look out for while managing your cholesterol.

High in Iron

Soybeans are packed with iron about 9 mg per cup, so much so that a cup of soybeans contains 49% of the recommended daily intake of iron. Fermented soy protein has 83% per cup, making this a great meal plan addition for athletes, weight lifters, resistance training, and anyone wanting to increase muscle mass.

The daily iron intake in soy is also significant for those with minor iron deficiencies. For example, people following a vegetarian or vegan diet have a high risk of developing anemia mainly because most iron in a traditional diet comes from animal protein.

Consuming soy protein provides that added boost of iron needed. Whey protein is another example of an iron-rich substitute but should be avoided if you’re lactose intolerant.

Reduces High Blood Pressure

In general, soybeans are a high protein, low carb food, beneficial for those suffering from hypertension [15]. Along with the isoflavones, soy is rich in amino acids like Arginine, which helps to regulate blood flow, blood pressure levels, and may help manage heart disease [16].

However, studies conducted do not clarify if these results are only in those suffering from high blood pressure or if healthy adults experience the same benefits from increased isoflavone intake.

Does soy isoflavones reduce blood pressure in people with normal and high blood pressure?

soy isoflavones
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Soy isoflavones shows to have a greater effect on people with hypertension

is soy bad for men Impact of soy isoflavone on blood pressure

Lowers Blood Sugar

Not only do soybeans initiate the lowering of blood glucose levels, but isoflavone may help lower insulin resistance by improving the body’s tolerance for blood sugar and improving insulin sensitivity [17]. This is something found in both soy food products as well as soy supplements. 

But like other studies found on soy’s effects and benefits, more testing must be done to confirm these results.

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May Reduce the Risks of Some Cancers

It was once thought that including soy protein in your daily diet increased your cancer risk, but over time and with more research, the opposite is true. Isoflavones have been linked to a lower risk of colon/colorectal cancer, digestive tract cancer and may protect against cancer of the large intestine, stomach, and lungs [18]

Research indicates that including a diet rich in soy may reduce the risks of some men developing prostate cancer which is the second most common cancer occurring in men worldwide [19]

Facts on Soy 

Now that we know soy is not a bad guy in this story and, if taken as recommended, has no adverse effects on men’s health, let’s take a look at some of the basic soy facts and how this little legume can transform your diet. 

Soy Nutrition

Soybeans are a plant-based protein with a truckload of vitamins and minerals such as potassium and antioxidants, all essential for reducing the risks of many severe conditions and chronic diseases, as well as fiber to keep you full and reduce cravings.

Soy is also a protein powerhouse, an essential component of sports nutrition, and a necessity for vegetarians everywhere.

Here’s a breakdown of common soy food products to give you an idea of their nutritional value:

  • Soy nuts: One cup is 189 calories, 16.9g protein, 8.1g fat, and 8.1 g of fiber.
  • Soy milk: One cup has 131 calories, 8g protein, 4.3g fat, and 10g of sugar.
  • Tempeh: A half-cup has 160 calories, 15 g protein, and 9g of fat.
  • Tofu: A half-cup of raw tofu has 94 calories,10g protein, 6g of fat, and 434 mg of calcium.
  • Miso: A paste made from fermented soybeans, miso has (per tablespoon) 34 calories, 2g protein, and just 1g of fat.

Types of Soy Products 

There are several types of soybean products described as either fermented and unfermented. Fermented soy is arguably the healthier form of soy. During processing, microorganisms are added to break down the nutrients in the soy, increasing the protein levels and making it easier to digest. 

Is Soy Bad for Men

Fermented soy foods include: 

  • Miso
  • Tempeh
  • Soy sauce
  • Natto
  • Tamari

Unfermented soy foods include:

  • Tofu
  • Soy milk
  • Soybean 
  • Edamame
  • Soy nuts 
  • Soy sprouts

Potential Downfalls of Soy and Soy Products

Soy, in general, is a healthy food product when consumed in its most natural form, but when soy is over-processed into food such as soy protein bars, soy-infused veggie sausages, and soy burgers, that’s when these products are more questionable and can lead to digestive issues such as nausea, constipation, and bloating [20].

It’s important to note that taking supplements such as isolated soy protein powders and pills for an extended period of time is not recommended and may cause health problems that are not found if eating large amounts of soy foods. 

Are All Soy-Based Foods the Same?

No. Soybean products can be either fermented or unfermented. The reduction of antinutrients during the fermentation process makes fermented soy a better option offering more of the health benefits mentioned earlier. 

You should also watch out for added ingredients in some soy foods, including added sugar, excess salt, and other chemicals included in highly processed foods. 

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Now that you know the truth about soy, we found and answered the most common questions men are asking about the possible effects of soybean products on their health.

Why Is Soy Protein Bad for Men?

Soybeans are not bad for men, but because of the estrogen-like ingredient isoflavones and the negative effect that high estrogen has on men, some jumped to the conclusion that soybean products are harmful, which is simply not true.

If you have concerns about your hormone levels and want to know which foods to avoid that could lower testosterone, we have information on alcohol and testosterone or you can check out what we found out about flaxseed and testosterone

Does Soy Cause Man Breasts?

No. Soy protein does not cause men to grow excess breast tissue or change the body in any way that looks more feminine. 

Does Soy Lower Sperm Count?

No. High soy consumption does not affect the sperm count or have any effects on testosterone levels.

Does Soy Cause Erectile Dysfunction?

No. Erectile dysfunction results from a number of factors, including low testosterone, which soy does not affect.

Is Soy Bad for Your Gut?

No. Soy is not bad for the gut health of humans. In fact, adding soy protein to a healthy diet reacts positively with the microorganisms working within the digestive tract and stomach to create a healthier environment that contributes to a healthy gut [21].


Myths about soybeans and soy consumption have been around for decades, but study after study proves that these rumors are absolutely not true. Soy is a healthy addition to any diet and includes a slew of nutrients, vitamins, and minerals that you need to maintain a healthy lifestyle. 

Including the recommended amount of soy is a great way to increase your plant protein, especially for people who follow a vegetarian diet, vegans, or anyone with underlying health concerns.

It’s recommended that you stay clear of excessive amounts of processed soy or soy supplements, which can have negative effects on your health.

If you want to know more about how soy consumption affects men’s health issues, including low testosterone, sexual function, and prostate cancer, don’t hesitate to seek professional medical advice from your local doctor or other health professionals.

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  10. JE;, Martinez J;Lewi. “An Unusual Case of Gynecomastia Associated with Soy Product Consumption.” Endocrine Practice : Official Journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists, U.S. National Library of Medicine, 
  11. AJ;, Michelfelder. “Soy: A Complete Source of Protein.” American Family Physician, U.S. National Library of Medicine, 
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