Should Men Avoid Soy?

One recent study suggests eating soy can lower a man’s sperm count and it’s generating much conversation and debate on the ‘net. I’m not putting a lot of stock in this one, but it’s interesting info.  This study is far from a “smoking gun” on the issue, but worth noting. Studies looking at the effects of soy on male fertility, testosterone levels, etc. have been inconclusive or contradictory. One study will find an association between X effect and another will not.

Readers should note that many of these studies are correlational studies. Such studies look for an association or “correlation” between one end point and another (say men eating X amount of soy and sperm count) and look to see how strong that association is. The problem with such studies is, correlation does not = causation. To look at true causation, direct intervention studies, such as the well known double blind placebo controlled type studies and variations of that, need to be conducted, and they are not perfect either, contrary to what some may think of them.

There’s an extensive amount of animal research also where the animals are fed large amounts of soy and or genistein – the major isoflavone and  phytoestrogen found in soy – and again, they are often contradictory.

However, large epidemiological studies (which are again correlational in nature) seem to find a reduction in male fertility (sperm counts) and reduction in testosterone levels, and some have suggested soy as one possible culprit. This latest study suggests soy may lower sperm count in men:

Soy Linked to Lower Sperm Count


CHICAGO (July 23) – Eating a half serving a day of soy-based foods could be enough to significantly lower a man’s sperm count, U.S. researchers said on Wednesday.

The study is the largest in humans to look at the relationship between semen quality and a plant form of the female sex hormone estrogen known as phytoestrogen, which is plentiful in soy-rich foods.

“What we found was men that consume the highest amounts of soy foods in this study had a lower sperm concentration compared to those who did not consume soy foods,” said Dr. Jorge Chavarro of the Harvard School of Public Health in Boston, whose study appears in the journal Human Reproduction.

“It was a relatively large difference,” Chavarro said in a telephone interview. Chavarro said studies in animals have linked high consumption of plant-derived estrogens known as isoflavones with infertility, but so far there has been little evidence of their effect in humans.

“We wanted to know if it would affect sperm production and could serve as a marker for the effects on the reproductive system,” Chavarro said.

Striking Difference

Chavarro’s team analyzed the intake of 15 soy-based foods in 99 men who went to a fertility clinic between 2000 and 2006.
They were asked how much and how often in the prior three months they had eaten soy-rich foods including: tofu, tempeh, tofu or soy sausages, bacon, burgers and mince, soy milk, cheese, yogurt and ice cream, and other soy products such drinks, powders and energy bars.

Because different foods have different levels of isoflavones in them, the researchers set a standard for serving sizes of particular foods. Then they divided the men into groups according to soy consumption levels. Men in the highest group on average ate half a serving per day.

“In terms of their isoflavone content that is comparable to having one cup of soy milk or one serving of tofu, tempeh or soy burgers every other day,” Chavarro said.

The difference was striking. Men in the highest intake category had 41 million sperm per milliliter less than men who ate no soy foods. A normal sperm count ranges from 80 million and 120 million per milliliter, and a sperm count of 20 million per milliliter or below is considered low.

“It suggests soy foods could have some deleterious effect on the reproductive system and especially on sperm production,” Chavarro said.

The researchers found the association between soy foods and lower sperm count was stronger in overweight men, which might suggest hormones are playing a role.

“Men who are overweight or obese tend to have higher levels of androgen-produced estrogen. They are converting a male hormone into a female hormone in their fat. The more body fat you have, the more estrogen you produce in your fat,” Chavarro said.

Chavarro said the study was not sufficient to suggest that soy intake would have health implications such as inducing infertility. Much bigger studies would be needed to answer that question, he said.

The Brink Bottom Line: As always, the dose makes the poison. Just as I would not recommend large amounts of soy to men, I would also not recommend they avoid all soy due to fear it will effect their sperm counts or testosterone levels. This one comes under the “everything in moderation” category. Men with low sperm count who need it to be higher, might want to cut out soy and retest, and lose some bodyfat also, to see if it increases their sperm counts.

Finally, I wrote an article on Soy a while back, and although it’s a bit dated, the general findings and conclusions still hold, and may be worth reading after this.

  1. Sjp98 15 years ago

    Soy is over rated and really has no benefits. In fact it is terrible for infants. The history on SOY: The Chinese did not eat the soybean as they did other pulses (legumes) such as the lentil because the soybean contains large quantities of a number of harmful substances. First among them are potent enzyme inhibitors which block the action of trypsin and other enzymes needed for protein digestion. These “antinutrients” are not completely deactivated during ordinary cooking and can produce serious gastric distress, reduced protein digestion and chronic deficiencies in amino acid uptake. In test animals, diets high in trypsin inhibitors cause enlargement and pathological conditions of the pancreas, including cancer. The soybean also contains hemaglutinin, a clot promoting substance that causes red blood cells to clump together. Check out the complete article: interesting!

  2. Jason 15 years ago

    Soy sucks. I was fed soy-milk from age 0 due to severe lactose intolerance at birth. Now, 30+ years later, I am on testosterone replacement therapy due to the damage said soy caused.
    Well, that is the best explanation the docs and I can come up with, nothing else makes sense for explaining my particular case of hypogonadism.

  3. Sjp98 15 years ago

    That proves the point in my mind Jason! Sorry to here of your experience. Hopefully you checked out the link to get more info.!

  4. Kevin 15 years ago

    I tried soy milk as I am intolerant to cows milk, it gave me the worst attack of gout I have had for a number of years, the skin on my foot still isnt right after a month, its wicked stuff

  5. Jerry 15 years ago

    Soy is recommended to help increase estrogen levels for menopausal women. This is Anti-Testosterone…

  6. Gus Gilbert 15 years ago

    Four years ago I had a physical in which my Doc advised me that my thyroid had swollen up and that I had high TSH levels of 5.0. He said to cut out any soy and also the nettle root (in my anti-estrogen formula). It took six months, but my thyroid went back to normal with a TSH of 1.6.
    It may have been due to the nettle extract, but I still avoid soy and nettle.

  7. Sjp98 15 years ago

    This is interesting to hear the testimonies on soy! I believe that if soy was eliminate from the market we would not miss it and a lot of aliments would suddenly go away. My first response has it all with the link. Need i mention more! It is very informative and worht looking at and passing on to friend.

  8. Dr.Chandan Baruah 15 years ago

    Isoflavones are found in about 300 different types of food including alcohol, mostly beer. But soy is highest source of isoflavone. Chemically isoflavone contains a substance which is similar to estrogen, the predominant female hormone which gives a woman all the feminine characteristics. So now a days lots of drugs are in the market which contain isoflavones from soy to treat menopausal symptoms where the amount of estrogen in a woman’s body is greatly diminished or absent. So isoflavone in large amount will be definitely harmful to a man because a male needs testosterone for a muscular body as well as other reproductive functions.

  9. Author
    Will Brink 15 years ago

    It’s important to note, “isoflavones” is a large group of compounds with varied effects on tissues. No general statements can be made there. Take a look at the post on flax for some additional info on the issue agonist/antagonist effects of phyto estrogen etc.

  10. Sjp98 15 years ago

    You be the judge? As the soy industry lobbied the Food and Drug Administration (FDA) for a cardiovascular health claim for soy protein, two senior FDA scientists, Daniel Sheehan and Daniel Doerge–both specialists in estrogen research–wrote a letter vigorously opposing such a claim. In fact, they suggested a warning might be more appropriate.
    Their Concern?
    Two isoflavones found in soy, genistein and daidzen, the same two promoted by the industry for everything from menopause relief to cancer protection, were said to “demonstrate toxicity in estrogen sensitive tissues and in the thyroid.” Moreover, “adverse effects in humans occur in several tissues and, apparently, by several distinct mechanisms.” Sheehan also quoted a landmark study (Cassidy, et al. 1994), showing that as little as 45 mg of isoflavones could alter the length of a pre-menopausal woman’s menstrual cycle.
    The scientists were particularly concerned about the effects of these two plant estrogens on foetuses and young infants, because “development is recognized as the most sensitive life stage for estrogen toxicity.”
    It wasn’t the first time scientists found problems with soy, but coupled with a Hawaiian study by Dr. Lon White on men, the controversy ended up on national television. While industry scientists criticized both the White study and the two FDA researchers (who are now disallowed from commenting publicly on the issue), other researchers weighed in on the anti-soy side. The tofu’d fight had begun….Requiem for a Thyroid
    One of the biggest concerns about high intake of soy isoflavones is their clearly defined toxic effect on the thyroid gland. You don’t have to work too hard to convince Dr. Larrian Gillespie of that. Dr. Gillespie, author of The Menopause Diet, in the name of scientific empiricism, decided to run her own soy experiment–on herself. She notes that she fits the demographic soy isoflavones are most marketed to: borderline hypothyroid, menopausal females.
    “I did it in two different ways. I tried the (isoflavone) supplements (at 40mg), where I went into flagrant hypothryoidism within 72 hours, and I did the ‘eat lots of tofu category,’ and it did the same thing, but it took me five days with that. I knew what I was doing but it still took me another seven to 10 days to come out of it.”
    Harvard-trained medical doctor Richard Shames, MD, a thyroid specialist who has had a long time practice in Marin, says that “genistein is the most difficult for the metabolic processes of people with low thyroid, so when you have that present in high enough concentrations, the result is an antagonism to the function of thyroid hormone.”
    “If you’re a normal person, and one in 10 are not normal, the effect [of 50 mg of soy isoflavones] may be fairly insignificant, but even a normal person can have problems at levels greater than that,” says Shames.
    Dr. Gillespie says the daily amount to cause thyroid problems may be as low as 30 mg, or less than a serving of soymilk.
    A number of soy proponents say the thyroid concerns are exaggerated and that if dietary iodine is sufficient, problems won’t likely happen. Not so, says Shames: “Iodine is a double-edged sword for people with thyroid problems, and for those people, more is going to increase their chance for an autoimmune reaction … throwing iodine at it is not going to be the protective solution.” Shames recommends limiting soy foods to a few times a week, preferably fermented or well cooked. SJP98 rests!

  11. Joe L 15 years ago

    I went off the prohormone AD1 and four months later began to include soy in my diet – roasted soybeans and soy milk. A week or two into it, I noticed pain under my left nipple. A few weeks later I noticed a lump the size of a golf ball cut in half. It grew consistently for four months to the size of a lemon until I had it cut out. Then it grew back and the right size started. I had assumed it was all from coming off AD1 but this was eight months later. I had used that stuff before and never had a problem coming off. They I heard soy was an estrogen and I knocked off the soy. They shrunk from the size of a lemon to the size of almonds. Unfortunatly they did not go away completely.
    I little while ago a guy I know had two lumps cut out, both the size of his fist. He too had been using prohormones but had not come off them. I mentioned that as he is obviously sensitvie to hormone imbalances, he should avoid plant and enviormental estrogens like soy. He nearly fell over. Guess what he was doing the month they grew. He had switched from whey to soy protein!
    I know that many people use soy without any obvious problems but it does have terrible effects on some.
    Stay away

  12. Sjp98 15 years ago

    Sorry to here about your situation. Soy has its short and long term ill effects on the body. There are people that do not show side effects, short term. However, study the history of soy and anybody will see that it was and is a known fact that it was seen as a money making opp. and the side effects short and long term are obvious. That is where my study took me. I am not a doctor [which makes my view less bias] nor am i a nutritionist. What i am is a person that researches for facts. What i look for is confirmation of a thought from several sources. It don’t make me 100% right per se. It makes me educated enough to say no to this product.

  13. Chef 14 years ago

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  14. learn to bartend 14 years ago

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  15. Luke M-Davies 13 years ago

    I remember a few years back when everyone hyped Soy as the next best thing! Well I’m glad that the word is spreading…it isn’t so great (especially if you are a man). You hit the nail on the head here – we cannot really avoid soy altogether as it is in many foods but men should not be reliant upon soy milk and other direct soy produce. It seems milk is the main concern so why not try coconut milk, oat milk, almond milk instead or no milk!

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