This article in the journal Nutrition was pretty simple. A 19 year old male sought treatment for lack of libido and sexual dysfunction. He had voluntarily started a vegan diet previously. The study measured the effects of ceasing a vegan diet and removing soy from the diet.

Yeah, this study has been around for a couple months. Apparently I was a sleep at the wheel that day. I think Keith Norris posted it on facebook yesterday. Thanks!

Previous research has focused on the beneficial effects of soy and its active ingredients, isoflavones. For instance, soy consumption has been associated with lower cardiovascular and breast cancer risks. However, the number of reports demonstrating adverse effects of isoflavones due to their estrogenlike properties has increased. We present the case of a 19-y-old type 1 diabetic but otherwise healthy man with sudden onset of loss of libido and erectile dysfunction after the ingestion of large quantities of soy-based products in a vegan-style diet. Blood levels of free and total testosterone and dehydroepiandrosterone (DHEA) were taken at the initial presentation for examination and continuously monitored up to 2 y after discontinuation of the vegan diet. Blood concentrations of free and total testosterone were initially decreased, whereas DHEA was increased. These parameters normalized within 1 y after cessation of the vegan diet. Normalization of testosterone and DHEA levels was paralleled by a constant improvement of symptoms; full sexual function was regained 1 y after cessation of the vegan diet. This case indicates that soy product consumption is related to hypogonadism and erectile dysfunction. To the best of our knowledge, this is the first report of a combination of decreased free testosterone and increased DHEA blood concentrations after consuming a soy-rich diet. Hence, this case emphasizes the impact of isoflavones in the regulation of sex hormones and associated physical alterations.

Here are the results:

Serum concentration of free testosterone

Serum concentration of total testosterone

Serum concentration of total testosterone

Percentage of free testosterone

Percentage of free testosterone

The left of the chart shows the subject’s testosterone levels upon initial testing, before cessation of vegan diet. The negative effects of the vegan/soy diet show a measured decrease after two weeks, but continued to improve for (at least) 724 days after quitting the vegan/soy diet.

The authors talk about proposed mechanisms (the wonderfully exciting world of isoflavones), et cetera, but I’ll leave it to someone else to bore you with those details.

Disclaimer bla bla bla

Obviously, a single individual can’t be assumed to represent the entire population.

  • And before we get into some lame cavemen died at 30 argument, a friendly reminder: “Modal ages of adult death… under traditional conditions seems to be just after age 70 years” –Source
  • There are older studies that say that soy has some benefits, but as the abstract says, “the number of reports demonstrating adverse effects of isoflavones due to their estrogenlike properties has increased.” The reasons for this are discussed specifically in the full-text of the article.

Not an isolated instance

Most veg*ns change to their way of eating for ethical reasons, most quit a veg*n diet because of health reasons. And contrary to what agrarian imperialists and feudal lords have been saying for a few thousand years, most of the ethical reasons are bogus as well.


Do your body and your planet a favor by avoiding soy. Seriously. Well, I mean… unless this is your goal… (Hey, I’m not judging)

Update: Mellisa McEwen wrote a post about this study that’s worth checking out.

  1. Don Matesz 13 years ago

    “Most veg*ns change to their way of eating for ethical reasons, most quit a veg*n diet because of health reasons.”

    Andrew, I don’t think the reference you gave supports that statement. That PT article was based on a survey of only 77 self-identified ex-vegetarians.

    Your statement could be taken to suggest that ‘most’ vegetarians quit being vegetarians, because they have declining health.

    But that PT survey does not establish that most vegetarians quit being vegetarians at some point. That would require a very large longitudinal study that starts with enrolling new and established vegetarians, then follows them to find out how many eventually decide to quit being vegetarians, and for what reasons.

    Starting with people who have already quit, as in this PT article, per force biases the results.

    Of the 77 ex-vegetarians surveyed for that PT article, only 35% (not even a simple majority) said that ‘declining health’ was the reason that they stopped eating a vegetarian diet. That means 65% stopped for other reasons; i.e. most stopped for reasons other than declining health.

    Some of those reasons seem silly to me: “About a quarter of our ex-veggies described the hassles they said were associated with strict vegetarianism. They complained that it was difficult to find high quality organic vegetables in their local supermarkets at a reasonable price. Others began to resent the time it took to prepare meatless dishes, and some said they simply grew tired of the lifestyle.”

    Who said you have to eat organic vegetables to be vegetarian? Vegetarian means avoiding animal products, not eating only organic vegetables.

    Suppose that someone said that he gave up omnivory its hard to find high quality organic grass fed meat. I would agree that it is hard to find such meat, but if you really thought omnivory was the best choice, wouldn’t you just buy the next best option?

    The prep time ‘reason’ is equally silly. Who said you have to make time consuming dishes? Why not make simpler dishes?

    Unfortunately I don’t have access to the full text of the case report. The abstract mentions ‘large amounts’ of soy products, and this individual was a type 1 diabetic. Dose makes the poison, so it is very important to know what dose was involved in this case.

    To my knowledge, larger studies and randomized trials have not established a universal testosterone depressing effect of soy products.

    “Soy milk intake was not associated with serum concentrations of testosterone, free testosterone, androstanediol glucuronide, sex hormone-binding globulin, or luteinizing hormone. These results suggest that soy milk intake, as a marker of isoflavone intake, is not associated with serum sex hormone concentrations among free-living Western men.”

    “Only three intervention studies reported hormonal effects of soy isoflavones in men. These recent studies in men consuming soyfoods or supplements containing 40–70 mg/d of soy isoflavones showed few effects on plasma hormones or semen quality. These data do not support concerns about effects on reproductive hormones and semen quality.”

    “This investigation shows that 12 week supplementation with soy protein does not decrease serum testosterone or inhibit lean body mass changes in subjects engaged in a resistance exercise program.” In fact this study showed an INCREASE in TEST/EST ratio after supplementation with soy protein.

    Obviously a 19 year old type 1 diabetic is metabolically challenged in ways that might influence how any particular food or diet plan might affect him. If he takes to eating ‘large amounts’ of a food that may be neutral or beneficial in small amounts, and gets adverse effects, I find it hard to generalize this to the whole population.

    • Andrew 13 years ago

      Indeed, studies from a decade ago show some support for benefits of soy. With the massive agri-business gestapo cashing in on their wundercrop, it's unlikely that we'll see a monolithic damning of soy in the literature.

      One quick point, the last study you referenced is for isolated soy protein. We're going to have the same difficulties getting anything useful out of studies like that as we would comparing whole milk to whey protein.

      That's all I have time for this second. I'll look more closely at this stuff if someone else doesn't beat me to it.

    • @toddulent 13 years ago

      I just posted in an online community I'm part of about how I went from vegan to paleo because of health reasons. Three doctors and a specialist all recommended a vegan diet with lots of soy protein to help eleviate IBS. The IBS didn't clear up and, in turn, I developed massive allergies, lowered libido, ED. All of that cleared up, not to mention the congestion from too much dairy consumption, farily quickly on the paleo diet, most within two weeks. At this point, I am reluctant to even call it a diet. I plan to stick to this for life.

      • Matt H Kennedy 12 years ago

        Well done! By the way, you CAN call it a diet, as diet literally means “way of life”.
        The common interpretation of the word diet as a ‘short term’ eating regime is wrong . 😉

      • Roger Robie 12 years ago

        Yeah it’s kind of like supporting Ron Paul, paleo diet just MAKES GOOD SENSE

    • Brent 13 years ago

      The studies you cite do not distinguish between vegetarians and non-vegetarians in their subject pools. Results may have differed if they were vegetarian subjects. Which leads one to wonder whether it's the soy or the lack of meat, or the combination of both, that leads to impotency.

      The third study you cite is on isolated soy protein, not soy products in general.

    • Andrew 13 years ago

      Re: the pro-soy supposedly not-anti-soy studies linked.
      Study 1
      Criticism 1
      Mean isoflavone intake per day in this study was broken down into 3 groups: 5.55 mg/d, 26.7, and 50.9 mg/d. At these levels, it is likely that the dose-response relationship demonstrated in the study from the OP would be completely missed. Siepmann, et al discussed this.

      Criticism 2
      More recent studies directly refute the findings of the study you cite — particularly the part you quoted.

      "CONCLUSIONS: These data suggest that higher intake of soy foods and soy isoflavones is associated with
      lower sperm concentration"
      – "Soy food and isoflavone intake in relation to semen quality
      parameters among men from an infertility clinic
      " (2008)

      Criticism 3
      Epidemiological studies are always subject to data mining, and tend to be suspect. They don't hold a candle to dietary interventions.

      My Conclusion: The methodology is weak, and newer studies refute the findings. Translation: does not support any claims that soy consumption is a good idea for humans.

      Study 2
      Criticism 1
      The studies referenced in this review were for 1, 2, and 2 months. Considering the study in the OP showed significant increases in T levels well beyond this timeframe, it is easy to see the weaknesses of reviews of such short duration studies.

      Criticism 2
      Same as Criticism 2 above.

      My Conclusion: Study 2 seems sufficiently debunked.

      Study 3
      Sorry, I'm bored with these junk soy propaganda studies. Their very existence in such weak form (while making such strong claims) is just more support for my political argument that agriculture is imperialism. It's like a redux of The China Study pap.

      Additional Studies Showing Lameness of Soy
      Multiple studies show soy contributing to reproductive problems (among other negative effects) in mice, and are theorized to be applicable to humans. However, human studies have proven difficult (ethical reasons, etc.). See:

      "Early Life Exposure to Isoflavones Adversely Affects Reproductive Health in First but Not Second Generation Female CD-1 Mice" The Journal of Nutrition (2011)

      "Early Exposure to Soy Isoflavones and Effects on Reproductive Health: A Review of Human and Animal Studies" Nutrients (2010)

      And in other news…

      "Prospective epidemiological studies for the evaluation of the effect of phytoestrogens alone, and in combination with other estrogenic chemicals, are lacking, yet possible adverse effects should not be taken lightly. – "Soy as an endocrine disruptor: cause for caution?" Journal of Pediatric Endocrinology & Metabolism (2010)

      • Roger Robie 12 years ago

        Here’s a study for you: Heavy intake of soy milk and I can hardly get it up….  Cut the soy milk out and Schwing!

  2. Don Matesz 13 years ago

    "Steroids in Adult Men With Type 1 Diabetes: A tendency to hypogonadism "

    "Adult men with fairly controlled type 1 diabetes without complications who are treated with subcutaneous insulin have a tendency to hypogonadism, as reflected by lower free testosterone levels in the presence of similar total testosterone levels and higher SHBG levels. "

    So it appears that low free testosterone is a characteristic of type 1 diabetic men using insulin, regardless of soy or animal food intake.

    Another reason I find it difficult to generalize from a this case of a type 1 diabetic to the general population.

  3. Andrew 13 years ago

    "it appears that low free testosterone is a characteristic of type 1 diabetic men using insulin, regardless"

    Ahhh… I am totally late for other stuff… so again… quickly… this study mentions that specifically:

    "The medication of the present patient included insulin, ramipril, and atorvastatin. These substances are not known to affect the synthesis or activity of testosterone. It is therefore unlikely that his medication could have accounted for the alterations seen on the hormonal level."

    So… to these authors at least, it does not appear that insulin explains this effect.

  4. Ken 13 years ago

    Somebody ought to post this for a Chinese audience.

    All that soy product offset by all those Chinese herbs to promote virility.

    Maybe the Chinese would sport better wood if they just dropped some tofu off the list and cut back on soy sauce.

    • David Csonka 13 years ago

      I keep reading in certain places (I have no citations at the moment) that consumption of soy in Eastern cultures is now significantly lower than in the West, and of a different variety.

      Whereas in China for instance, fermented soy is popular, and is treated more as a garnish and addition to the meal, in the West soy is straight up eaten raw or as the main course.

      All anecdotal, but this is stuff I've repeatedly read on the interwebs lately about the "But Chinese people eat tons of soy argument".

      • Andrew 13 years ago

        This study mentions the relative amounts of isoflavones in the diet, but didn't specify total soy consumption via oils, etc.

        Average Western diet 2 mg/d
        Other soy studies ~150 mg/d
        This study ~360 mg/d

        That's [apparently] why they repeatedly emphasized the vegan thing. This guy was replacing basically all of his protein needs with soy. They don't mention it, but it's probably somewhat similar to the way I used to eat… using Morningstar farms soy-based fake sausage bullshit in place of real food, but… all the time.

        There's probably some insight here along the lines of dose-response. I'd speculate that the folks in the ~150 mg/d are experiencing some problems, but just not as acutely as this guy at the mega-dose range.

  5. Victoria 13 years ago

    I've always loved (hated, really) the 'Soy phytoestrogens aren't relevant. Oh- but post menopausal women should eat lots of soy because it will give them relief from symptoms of menopause'. Umm- either they're physiologically active or they're not, make up your mind!

    I've wondered for a while about the effects of soy formula for infants. Seems like something we're going to look back at in a generation or 2 and think 'What the hell were those people thinking'.

    • Andrew 13 years ago

      Yes. Agreed. See my comment to Don above. The referenced studies have direct bearing on your comment.

    • Anastasia 13 years ago

      Victoria, I find it interesting that soy infant formula always gets the benefit of the doubt with arguments running along the lines of: “we can’t detect anything wrong, and we don’t have any long term follow up studies, and the Asians are eating soy, and all the scary studies are done on neonate mice so it doesn’t count, and it’s such a large share of the market, so we assume that it’s totally safe”.

      Plus I don’t just want to know that my child’s major food source in the first 6 months will not cause any future reproductive and endocrine disruptions. I want to know that it is also beneficial to their overall development.

      Like the authors in this review (Tuohy PG, Soy infant formula and phytoestrogens (2001) Journal of Paediatrics and Child Health, 39(6);401-405, (

      “Despite the absence of adequate scientific research that quantifies the level of risk to infants, most would argue for a precautionary approach to be taken in situations where there are potential developmental effects from the consumption of pharmacologically active compounds in infancy and childhood.”

      • Victoria 13 years ago

        Yeah. I think the whole soy-formula thing is going to have a really nasty ending. I can see the class-action lawsuit now…

        When you look at the complexities of breast milk (I think it's fascinating how growth factors, hormones, and nutrient levels in breast milk vary over time), it's hard to imagine a formula can adequately replicate it. Sure it'll sustain life, but it's definitely not optimal. You have to wonder what role breast milk composition might play in epigenetics, and perhaps what implications that may have in metabolic disorders. There was a fun review in Nature not too long ago:

        Not to mention, breast feeding is better for Mum too!

  6. Emily Deans 13 years ago

    Brain aging and midlife tofu consumption – observational, sure, but cute couple comparisons:

    • Andrew 13 years ago

      Thanks. Interesting!

      "We hypothesize that regular dietary exposure to soy isoflavones over many years during middle life may be associated with the appearance of accelerated brain aging in later life attributable to chronically sub-optimal neural plasticity."

      This definitely adds to the picture that long-term soy exposure is a beast that may not show up in 30 or 60 day studies. And… this type of hard to suss out long-term effect is exactly why I think the paleo framework is the most powerful game in town when it comes to making decisions based on limited information.

  7. Cade Krueger 13 years ago

    Hey you are worth reading. You know things and a bit of comedy sprinkled on top. Never die.

  8. Nick Baran 13 years ago

    I’ll have been vegan for 20 years this February. I’ve never had a problem with getting an erection or my libido, and I haven’t developed breasts. Too much of anything is a bad thing. You can still be vegan and eat like shit or you can eat a balanced diet whether you’re vegan or your an omnivore. If you live entirely off of processed foods like prepackaged soy-based meat and dairy substitutes you’re health is going to be about as balanced as someone who lives entirely off of McDonald’s. People need to use common sense.

  9. Roger Robie 12 years ago

    To all you academic types nitpicking the “studies”, I got one for you. When I drink large portions of soy milk I cannot get it up, mmkay? Cutting out the soymilk and nothing else from diet and badda bing, back to normal. Simple as that… I find unfermented soy products DISGUSTING now.

  10. Jeffrey 12 years ago

    I haven’t gotten it up since I began a vegan diet

  11. Milette 12 years ago

    Hi Jeffrey. Me too!

  12. EVOLVINGJEFF 12 years ago

    Guys…I have the same problem! Good thing I prefer the bottom…

  13. SoyBoyToy 12 years ago

    Hi everyone. My name is Dorian. I am logged on through my husband’s account. I just recently found out that he is gay. He is emphatic that it is due to me having a BMI of 488.7; however, I KNOW it’s the vegan diet that caused this!

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