Soy Sorry: Part 1 – Soy Does Not Cause Man Boobs! So What Does Cause It?


Soy doesn’t feminize men. What actually causes man boobs and feminization of men?

This ‘Part 1’ of the Soy Sorry investigation shows that the causes of feminization of men (particularly the most visible one of all–man boobs) have virtually nothing to do with soy.

There’s no better place to start a discussion on feminization worries in men than with an up-close and personal look at man boobs. When men worry about soy, they’re worried that there’s something in soy that makes men more feminine. And by “feminine” I mostly mean boobs.

Man boobs. Also known as ‘moobs.’ Dudes do not want moobs.

What even are man boobs?

Man boobs have a real medical name: “gynecomastia.”1 I sometimes see people call it “gyno” for short.

There are two types of man boobs. Pseudo-gynecomastia and true gynecomastia.

a) Pseudo-gynecomastia

This refers to man boobs from fat in your chest as a result of being overweight.2 In other words, this is flabby fat tissue (or “adipose tissue” as scientists and doctors call it), and it’s caused by having high body fat. The cure: lose fat, which you can do by diet, exercise, caloric deficit, etc.

b) True gynecomastia

This is the type of man boobs that men truly fear. And it’s the type of moobs that will be the focus of the rest of this article. Because it’s not fat tissue in your chest that can be eliminated by reducing your body fat. Rather, it’s glandular tissue that’s been enlarged by other bodily processes.3 4 5 6 7

For men with with man boobs, there’s a good chance their moobs are a combo of both pseudo gyno and true gyno. In other words, some dudes have chests that have excess body fat tissue and excess glandular tissue. Not surprisingly, there’s a huge correlation between man boobs and obesity.8

For the vast majority of dudes with moobs, it’s usually a few centimeters of breast growth, which researchers typically call “asymptomatic” gynecomastia.9 It’s minor, but a few centimeters of mannaries can be noticeable and make men self-conscious.

To understand what causes true gyno, you need to understand hormones

The exact cause of the enlarged glandular tissue (ie, true gyno) is subject to a ton of discussion. The purpose of this article is to share what the overarching scientific understanding is, based on statistics, reports, and studies.

And that understanding is that true gyno is likely due to a hormonal imbalance where there’s too little of the primary male sex hormone (testosterone) and/or too much of the primary female sex hormones (estrogen and progesterone).

That makes sense, because one of testosterone’s effects is to promote masculine characteristics, such as keeping breast tissue small.10 11 Meanwhile, one of estrogen’s functions is to promote feminine characteristics, like increased breast tissue.12 Same goes for progesterone, which also triggers breast growth.13

When estrogen or progesterone levels are too high, and increased levels of either growth hormone or the hormone IGF-1 are present, then you’ve got a perfect recipe for moobs.14

For the sake of not making this blog post twice as long, I’m going to focus on testosterone and estrogen. These are the main characters in the man boobs and feminization story. There are other hormones with very important roles, too. But, to cut to the chase: the feminization fears about soy center on soy’s relationship to the two primary sex hormones — testosterone and estrogen.

All men, believe it or not, naturally have estrogen in their bodies.15

Some people mistakenly believe that men don’t have estrogen; they believe it’s a hormone that only women have. Not true. Even if you’re the most committed paleo keto caveman eater who has never touched soy (or a woman) since he was born, and who only eats bone broth from the skulls of fossilized alpha-male wooly mammoths, you still have estrogen in your body. Naturally.

In fact, estrogen actually plays many crucial roles in men and in the development of masculine features, including an important role in the production of sperm!16

Men generate estrogen in a number of ways. The vast majority (80%) is generated throughout the body by an enzyme called aromatase.17 Aromatase plays a huge role in this story, so be sure to remember the name. It travels around the body and converts testosterone into estrogen. This makes it a double edged sword–it increases estrogen and decreases testosterone. Men produce aromatase in their testicles, their brain, and in body fat tissue, among other places in the body.18 As I’ll get into later, there are certain foods and substances that can either increase or decrease aromatase production.

Hormones are confusing.

If it’s not already apparent: studying hormone levels is a difficult task. Add in this frustrating fact: hormone levels change significantly in our bodies just because. You could have high testosterone in certain seasons, but not in others.19 You could have high levels of a certain hormone at one point in the day, but not in another point in the day.20

Plus, even the actual process of testing hormones is not standardized. Some studies use blood serum tests and some test saliva, while many other studies test levels in urine and poop. When it comes to the urine studies, many researchers don’t agree whether the amount of hormones in urine is even a reliable indicator of how many hormones are in blood or absorbed in a particular tissue in the body, or whether those hormones were even bioavailable to begin with.21 22 23 24 After all, if you excrete a hormone in urine or poop, your body is getting rid of it. It doesn’t necessarily mean your body is being affected by it, or that your body has absorbed it into your tissues.

There’s also the fact that other compounds and bodily mechanisms play a huge role in hormones. For example, there’s a protein the body makes called the sex hormone binding globulin (SHBG), which, among other functions, binds to and inactivates testosterone and, to a lesser extent, estrogen. Typically the more SHBG a person has, the less active testosterone and estrogen they likely have.25 26

Vegans have actually been found to have higher testosterone levels than either vegetarians or meat eaters (!), although it’s not necessarily bioavailable testosterone, because SHBG levels appear to be higher among vegans, too.27

What causes man boobs?

In other words, what causes the body to produce too much estrogen and/or too little testosterone, leading to enlarged glandular tissue in the chest?

I’ve found seven big causes.

The first three causes make up the overwhelming majority of true man boob cases in the world. Frustratingly, these causes are due to hormone fluctuations that don’t happen for any specific, avoidable reason. They happen just because.

I know–that’s an annoying reality. Basically, it’s a seemingly unavoidable thing that just happens, even if you’re a caveman who lives on raw bone marrow. This means that the vast, vast majority of man boob cases have nothing to do with soy or any other food. This is a huge take-home message: if you find yourself with man boobs, it’s almost definitely related to something other than something you eat or drink. Instead, it’s likely a natural (albeit unfortunate) thing that happens to a huge number of males at different stages of their life, simply because hormones go kind of crazy at those particular ages. Those age stages are: infancy; teenage years; and middle-age.

Cause 1: Being a baby

Between 60% and 90% of newborn boys have man boobs!28 (or boy baby boobs…) Why? It’s not because up to 90% of babies have become pretentious vegans who eat tofu scrambles every day. Rather, it’s because they have a lot of their mother’s estrogen flowing through them.29 This is a temporary form of gyno that goes away eventually.

Cause 2: Being middle-aged

Between 25% and 70% of men older than the age of 50 have some form of gynecomastia.30 Why? It’s not because two-thirds of the country’s 50 year old men have demanded soy chik’n burgers after a day of golf. Rather, it’s due to the fact that testosterone production declines with age (ie, hypogonadism), leading to a hormone imbalance.31

Cause 3a: Being a teenager

Between 60% and 70% of teenage boys develop some degree of gynecomastia.32 Why? It’s not because high schools are serving tempeh at prom. It’s because hormone levels fluctuate during puberty.33 Puberty occurs for most boys around the age of 12 or 13 through about 16 or 17.34 For the majority of the teenage boys who develop man boobs, it goes away naturally with the passage of time, usually about six months to two years after the initial onset.35

However, for many of these teenagers, the condition doesn’t go away as they age. Some teens develop a degree of man moobs that remains present event after they’ve gone through puberty. Which brings us to the next bunch of causes.

What about men in their 20s, 30s, and 40s?

Between 33% and 41% of men in this age bracket have some degree of man boobs.36 That’s a significant number of men with moobs. But how? They’re not in one of those three age brackets where hormones naturally go crazy (baby, teen, middle-age). This is where you might think soy could sneak its way in. But no, even among this group, the causes have nothing to do with soy.

Cause 3b: Man boobs that never went away from puberty

Most of the 60% to 70% of teenage boys who develop some form of man boobs during puberty have them fade away naturally, with the passage of time–usually between six months and two years from the initial onset of the moobs.37 However, in a study of man boob cases of men between the ages of 19 and 29, it was found that 32% had what’s called “persistent pubertal” man boobs.38 Other studies pin this type of man boobs on somewhere between 10% and 20% of cases.39 Again, these are man boobs that initially arose during puberty–say, at 14 or 15 years old. But, by unfortunate luck, the glandular tissue in the chest never went away after the typical six months to two years.40 This isn’t because high school cafeterias are dishing out tofu hot dogs. It’s another just because. In other words: blame luck.

For the vast majority of man boobs cases, everything above this paragraph explains the likely cause. If you’ve got some excess tissue in your chest area, it’s likely due to hormone imbalances that happen (or happened) at these three particular stages of life. Again, that’s a very frustrating reality. I can see the appeal of wanting to blame it on something avoidable, like soy. How nice would that be? Yet the statistics point to man boobs being something that just happens to a huge proportion of men, no matter what they eat.

Maybe soy sneaks its way into the other leading causes?

Spoiler alert: nope. It doesn’t. The other causes have nothing to do with soy.

Cause 4: Being overweight

The many curves of body fat

Body fat creeps its way into the man boob conversation in many different contexts. It was mentioned above because there’s a huge correlation between man boobs and obesity. Body fat was also mentioned earlier because when body fat tissue that collects in the chest is, that condition is called psuedo-gynecomastia. But fat also earns a featured spot on this list of causes of true gynecmoastia as well.

Body fat can be a cause of true (glandular) gynecomastia because fat tissue is a location where the body produces aromatase, that enzyme that converts testosterone into estrogen.41 The more body fat you have, the more aromatase you likely have.42

As one medical publication puts it, “It’s appropriate to think of fat as an endocrine organ or gland, producing hormones and other substances that can profoundly affect our health . . . [I]t’s becoming clear that excess body fat, especially abdominal fat, disrupts the normal balance and functioning of these hormones.”43 Indeed, weight has a bigger impact impact on testosterone levels than aging. As weight goes up, testosterone levels go down.44

Cause 5: Certain drugs

At least 25% of gyno cases are from those who take a prescription drug that causes it. According to a review of the evidence: “The drugs definitely associated with the onset of gynecomastia are spironolactone, cimetidine, ketoconazole, hGH, estrogens, hCG, anti-androgens, GnRH analogs and 5-α reductase inhibitors. Medications probably associated with gynecomastia include risperidone, verapamil, nifedipine, omeprazole, alkylating agents, HIV medications (efavirenz), anabolic steroids, alcohol [I’ll dig deeper into alcohol below] and opioids.”45

Many other drugs have also been linked with gyno, including amphetamines (such Adderall and Vyvanse; or illegal amphetamines like crystal meth), antibiotics, certain anti-depressants, ranitide (aka, Zantac), marijuana, and other drugs as well.46

It almost makes you wonder: is there a drug that doesn’t feminize men?!

Even the medicine cabinet mainstays like Advil, Tylenol, and aspirin have been found to negatively affect testosterone levels in men.47

An extra shout-out for steroids:

One interesting thing: anabolic steroids are mentioned as a drug that is likely to cause man boobs. Anabolic steroids (and testosterone replacement therapy) are basically synthetic forms of testosterone.48 Usually they are taken as a topical gel or a direct injection.

How is it possible that adding testosterone would increase the likelihood of man boobs? Wouldn’t the opposite be true?

One reason is that the testosterone supplements get converted into estrogen by that pesky aromatase enzyme.49 Meaning–there’s more testosterone in the body for aromatase to convert into estrogen. Another possible reason is that supplementing testosterone inhibits the body’s own natural testosterone production.50 In other words, adding outside testosterone can cause your body to make less of its own natural testosterone.

Cause 6: Certain diseases

Some diseases are known to cause man boobs, particularly liver disease, kidney disease, thyroid disease, hormonally active tumors, and Klinefelter’s syndrome.51 In one Mayo Clinic study of 132 adult men with gynecomastia, 83% of man boobs cases were shown to be caused by either a prescription drug or a disease.52

Cause 7: Industrial xenoestrogens

Xeno-estrogens are a broad category of mostly industrial chemicals that have estrogenic effects in people.53 54 55 56 This category includes chemicals that are called “persistent environmental pollutants” or “endocrine disruptors.”57 58

Several authorities consider xeno-estrogens and environmental pollutants to be a likely cause of gynecomatia.59 60

Overall, xenoestrogens are considered weaker than actual estrogen, like the true estrogen found naturally in men and women. There are a ton of chemicals that are classified as xenoestrogens. I’ll delve into some of the more notable ones.

You’ve probably heard of BPA (and its lesser known cousin, ‘BPS’), which are usually found in plastics. Overall, BPA is considered to be on the weaker side of the estrogen spectrum.61 62 Yet, there’s still debate among experts about exactly how worrisome BPA is in terms of its estrogenic effects.63 One study found that male breast tissue is particularly susceptible to BPA, even at low doses.64 65

Even “BPA-free” plastics contain other, lesser-known estrogenic chemicals.66 67 I was curious whether “sous vide” plastic has similar concerns. Sous vide is a type of cooking where food (usually meat) is sealed in a soft plastic wrap and cooked for extended periods of time. It turns out, the companies that manufacture sous vide plastics don’t disclose what specific additives they use, and it seems likely that if they ever do, they’ll be found to be estrogenic (even if it’s not BPA) because the base components need additives to make the plastic functional.68

Phthalates are another chemical used in many plastics and they have also been found to be estrogenic and have been linked to gyno.69 Parabens are estrogenic compounds used in cosmetic and personal care products.70 So are the active ingredients in most sunscreens.71

Meat, milk, cheese, fish, and eggs are common source of a huge array of xenoestrogens.

I’ll dig deeper into this fact in Part 3, but it deserves to be mentioned here as well. Meat, dairy, and eggs contain a lot of these industrial xeno-estrogens. This is particularly with phthalates, dioxins, alkylphenols, PCBs, heterocyclic amines, and polycyclic hydrocarbons.72 73 74 75 76 77 78 79 8081 82 83 84 85 86 Even xeno-estrogenic pesticides, which are sprayed on feed crops, are fed to livestock, and then dissolve into animal fat.87 Yikes. In fact, meat and dairy products tend to be–by far–the biggest dietary source of exposure of almost all of these xenoestrogens.

When you read about many of these industrial xeno-estrogens, you’ll often read that they “work their way up the food chain” or that they “bioaccumulate,” usually because animal fat does a good job storing these chemicals. That’s all just a longer way of saying: the biggest sources of these xenoestrogens are meat and dairy.

The Trend of Lower Sperm Counts

There’s a trend that gets reported a lot in the news: sperm counts and testosterone among men are declining across the board, as time goes on.88 It’s happening to men, in general. What could be causing this? Scientists don’t have a definite answer. But the most commonly mentioned theory is that the culprit is exposure to industrial xenoestrogens. That exposure increased a ton in the post-World War 2 industrialized world. Earlier generations have loads of xenoestrogens in their bloodstream. According to the theory, those industrial xenoestrogens can change the way genes are expressed. And those changes are inheritable from one generation to the next. The take-home message: men today might be more feminized because of their parents’ exposure to industrial xenoestrogens. This phenomenon is expected to continue. Not because of soy, but because of the industrial chemicals mentioned above.

Dishonorable Mention: Alcohol

On almost every reputable list of what causes man boobs, you will find alcohol prominently displayed.89 90

Alcohol is even mentioned above as a “drug” that likely causes gyno.

I think alcohol (or ‘ethanol’ as scientists call it) deserves a special shout out because it’s so prevalent and common. I don’t know too many men who don’t drink alcohol at least semi-regularly. When I was in my early to mid 20s, it seemed like most guys I knew were drinking very, very regularly. That’s the college and post-college culture.

There are many pathways through which alcohol can feminize men.

The fact alcohol is such a potentially feminizing substance is pretty shocking. Alcohol, especially beer, has connotation for being a masculine product. Watch most beer or liquor commercials, and the message is usually some version of “Want to be a manly man? Drink our beer [or whisky, or tequila, or vodka, etc.].” It’s not surprising that a big reason why men drink beer is an effort to come off as more manly.91 Yet, that same drink may literally be making men more feminine. That makes the truth about alcohol pretty shocking.

Before I get into this–I want you to know that I don’t take too much pleasure in the estrogenic pounding that alcohol is about to get. The vast majority of alcoholic drinks are vegan. One reason I made this blog is to show how manly I think veganism can be. Here, I’m tearing down a mostly vegan product that has a reputation for being manly in society. Such products are in short supply.

Fellas, hold on to your moobs, you aren’t going to like this.

Alcohol may lower testosterone.

This has been shown in multiple studies and reports.92 93 A big reason why: alcohol damages the testes (aka your balls). This is the organ where men produce testosterone.94 95

Occasionally, a study comes out that shows that moderate alcohol consumption can have a minor increase testosterone in the short-term. For example, one study from 2003 found that men who drink a small amount of alcohol get a slight, temporary increase in testosterone.96 This study is sometimes cited as proof that you can have a drink or two because a small amount of alcohol won’t reduce testosterone. But the very same researchers released a study the following year in 2004, and found that drinking small amounts of alcohol does reduce testosterone.97 Considering the 2003 study is such an outlier compared to the consistency of other studies (that connect alcohol with lower testosterone),98 99 100 101 102 I tend to think the 2004 study is probably closer to the truth.

Another study that gets cited to prove alcohol is pro-testosterone is a study that connected red wine with an increase in testosterone.103 But it’s not the alcohol in red wine that is believed to increase testosterone. It’s compounds found in red wine grapes that either raise testosterone or lower estrogen, particularly one called “resveratrol,” another called “proanthocyanidin,” and another called “quercetin.”

The compound ‘quercetin’ inhibits an enzyme that causes the body to pee out testosterone. By consuming foods with quercetin, you theoretically keep more testosterone in the body. And there are a lot of foods with way more quercetin than wine and grapes: red onions, capers, elderberries, radishes, buckwheat, cranberries, some lettuce leaves, among others, have more.104

Again, the vast majority of studies and reports show that alcohol decreases testosterone. Red wine might be a narrow exception, but only because it has these anti-estrogenic/pro-testosterone compounds in grapes.

Alcohol increases estrogen.105

The reason why: alcohol can increase the enzyme aromatase, which (as discussed earlier) converts testosterone and other hormones into estrogen.106 So not only can alcohol decrease testosterone, it can increase your own body’s production of estrogen as well.

It gets worse for alcohol. As many people know, one organ that alcohol is particularly damaging to is the liver.107 Guess which organ happens to play a major role in regulating estrogen. Yup, the liver.108 Most sources seem to pin liver damage on long-term and/or excessive drinking. So if you’ve been drinking regularly for a number of years, or if you drink too much during the occasional times that you do drink, alcohol might’ve disrupted some of your liver’s functions.

After all, as mentioned above in Cause 6, liver disease is linked with man boobs.

Alcohol is also caloric and can be fattening.

If you consume more calories than you burn, you’ll gain body fat.109 And body fat is connected to man boobs in many ways (as discussed above), including by producing the aromatase enzyme which converts testosterone into estrogen. Even a single shot of vodka–which is a favorite of people trying to watch their calories–has nearly 100 calories.110 That adds up over time. Alcohol also causes you to be hungrier, leading to an even greater caloric intake.111

Beer contains a powerful estrogenic compound.

It gets even worse for beer drinkers. In addition to the fact that alcohol can hurt your balls (which produce testosterone), and hurt your liver (which regulates estrogen), and promote the conversion of testosterone into estrogen, beer contains a potent estrogenic ingredient. Specifically, beer contains a highly active phyto-estrogen (phytoestrogens are sometimes called “plant estrogen.”)

Phytoestrogens are broad class of compounds found in plant foods. Importantly (and confusingly), phytoestrogens are not estrogen. The vast, vast majority of the phytoestrogens are either extremely weak or, believe it or not, are anti-estrogenic. The phytoestrogen found in beer, however, is an outlier. It’s called “8-PN.” It is not weak or anti-estrogenic. In fact, it’s often called the “most potent” phytoestrogen.112

8-PN is from the hop plant, which is used to make beer.113 8-PN binds to the particular estrogen receptors that promote breast growth.114 Worse yet, drinking moderate amounts of beer can provide the same amount of 8-PN as breast enlargement products that use 8-PN as an ingredient.115 Again, this is specific to 8-PN, which is in a class of its own when it comes to phytoestrogens. Other phytoestrogens have also been studied extensively and have been found to have the opposite true for them, as I’ll delve into in Part 2.

Alcohol is a triple threat.

Meanwhile, researchers and cancer organizations continue to warn people–both men and women–about alcohol. Even one single alcoholic drink a day may increase the risk of breast cancer, largely due to the effect that alcohol has on estrogenic activity in the body.116

So, we know that man boobs are caused by low testosterone, or high estrogen, or some combination. Alcohol may hit all of these points. If you want to see man boobs in action, a vegan potluck is probably not your place. Instead, go pull up a stool at your local dive bar.

Wait. So soy really doesn’t cause man boobs?

By sheer odds, if you’re a man, and you’re experiencing some form of feminization (such as man boobs), one of the above categories is almost certainly your culprit. Not soy. 

The answer to the question “What causes man boobs?” should really end here. This section summarized the leading scientific understanding on what causes it. Any other potential cause would be so statistically irrelevant that it would be a waste of time to discuss. Your mind should be satisfied.

I know you’re hungry for more.

The next section digs deep into the world of soy, and why people mistakenly believe it feminizes men.

Read on.

Click here for SOY SORRY: PART 2 – The actual science of soy and phytoestrogens

The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.


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  8. Epocrates 1
  10. Harvard Testosterone
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  18. Reproductive Biology and Endocrinology
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  117. None of this content is medical advice.

One Comment

  1. I’ve lived in Asia for half of my life and gynecomastia is pretty much non-existent. I saw one guy but it could of been psuedo along with the shape of the chest or location of the nipples. Other than that spotting an asian with gyno is like seeing a unicorn. Here in Korea, soy is pretty much in everything.

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