Soy Foods Associated with Lower Sperm Counts | Chris Kresser

Soy Foods Associated with Lower Sperm Counts


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A study recently published in Human Reproduction demonstrated that intake of soy foods significantly reduces sperm counts in men.

The study is especially significant because it is the largest study in humans to examine the relationship between semen quality and phytoestrogens (plant compounds that can mimic the physiological effects of the endogenous hormone, estrogen).

Dr. Jorge Chavarro of the Harvard School of Public Health and his colleagues found that men who ate the most soy food had 41 million sperm per milliliter less than men who did not consume soy products. The normal sperm concentrations for men ranges between 80 and 120 million/ml.

The association between soy food intake and sperm concentrations was even stronger in men who were overweight or obese, and 72% of study participants were. They also found the relationship between soy foods and sperm concentration was strongest in men with “normal or high” sperm counts.

Animal studies have linked the high consumption of isoflavones with infertility, but until now there has been little evidence of this effect in humans. Isoflavones are plant compounds with estrogen like effects and are found mainly in soybeans and soy-derived products.

What is particularly revealing is that the men in the highest intake group (who had the largest sperm count reduction) had a mean soy food intake of only half a serving per day. This is equivalent to having one cup of soy milk or one serving of tofu, tempeh or soy burgers every other day!

I don’t know about you, but I happen to know quite a few people who consume a lot more soy than than that on a regular basis. Sadly, many of them are children whose parents innocently believe that soy products are “healthy”. This is not their fault, of course; this erroneous and dangerous message has been aggressively promoted in the mainstream media for decades.

If the effect of such moderate servings of soy on adult males is so significant, what effect might soy foods have on developing boys who have not yet reached sexual maturity?

“Early puberty (caused by consuming soy products) may increase a boy’s chances of developing testicular cancer later in life, because it means longer exposure to sex hormones,” said University of North Carolina researcher Marcia Herman-Giddens.

Congenital abnormalities of male genital tracts are also increasing. Recent studies found a higher incidence of birth defects in male offspring of vegetarian, soy-consuming mothers.

What about babies? Preliminary studies indicate that children given soy formula go through puberty much earlier than children who were not fed soy products. A 1994 study done in New Zealand revealed that, depending on age, potency of the product, and feeding methods, infants on soy formula might be consuming the equivalent of up to 10 contraceptive pills a day. By exposing your baby to such large amounts of hormonal-like substance, you are risking permanent endocrine system damage (pituitary gland, pineal gland, hypothalamus, thyroid, thymus gland, pancreas, ovary, testis, adrenal glands).

Dr Chavarro speculates that the increased estrogenic activity caused by consumption of soy foods may have an adverse effect on the production of sperm by interfering with other hormonal signals. This effect could be strengthened further in overweight and obese men because men with high levels of body fat produce more oestrogen than slimmer men, leading to high overall levels of oestrogen in the body and reproductive organs.

If you’re wondering how soy continues to be so widely accepted and aggressively promoted as a “health food” in spite of the overwhelming evidence to the contrary, I recommend reading The Whole Soy Story by Kaayla Daniel, PhD, CCN. You can read introduction to this eye-opening book here.

The history of soy products and their designation as a “health food” is particularly revealing, as Daniel points out:

Early soy food promotion in America aimed at two specific markets—vegetarians and the poor—soy milk and soy cereals for Seventh Day Adventists, Bac-O-Bits and meat extenders for the budget conscious. But there was a lot of soy to sell and these markets were limited. There was so much to sell because the market for processed foods had experienced explosive growth since the 1950s—and most processed foods contain soy oil. The industry found itself saddled with a waste problem, the leftover sludge from soy-oil manufacture which it could either dump or promote.

The exigencies of corporate life naturally chose profit-seeking over disposal and that meant expanding the market, finding more ways to use soy ingredients in processing and convincing more people to pay money for soy-based imitation foods.

“The quickest way to gain product acceptability in the less affluent society,” said a soy-industry spokesperson back in 1975, “. . . is to have the product consumed on its own merit in a more affluent society.” Thus began the campaign to sell soy products to the upscale consumer, not as a cheap poverty food, but as a miracle substance that would prevent heart disease and cancer, whisk away hot flashes, build strong bones and keep us forever young. Soy funds for research enlisted the voices of university professors who haplessly demonized the competition—meat, milk, cheese, butter and eggs.

Soy is one of the “Big Four” cash crops in the U.S. and the funds for its marketing are enormous:

“Farmers pay a fee for every bushel of soybeans they sell and a portion of every dollar spent on Twinkies, TV dinners and the thousands of other processed foods that contain soy in one form or another, ultimately go towards the promotion of the most highly processed foods of all—imitation meat, milk, cream, cheese, yogurt, ice cream, candy bars and smoothies made from soy.

All soybean producers pay a mandatory assessment of one-half to one percent of the net market price of soybeans. The total—something like eighty million dollars annually—supports United Soybean’s program to “strengthen the position of soybeans in the market place and maintain and expand domestic and foreign markets for uses for soybeans and soybean products.”

And of course, these advertising dollars are largely responsible for creating the erroneous notion that highly processed soy foods are “healthy”:

“A survey of March 2004 health magazines reveals five-and-one-half pages of ads for products containing soy in Alternative Medicine (two of which promote soy as a solution to the problems of menopause); five-and-one-half pages in Vegetarian Times; and five pages in Yoga Journal. The ads that keep today’s health-oriented publications afloat aim at mainstream, not alternative, culture: soy milk ads feature faces of smiling children; high-protein bars create expressions of ecstasy on upside-down models; and a hostess who serves chocolate-covered soy nuts is the toast of her party.”

However, in spite of advertising and popular belief, processed soy products are not health foods. Because of their estrogenic effects, they act more like drugs in the body than foods.

And as we all know, drugs can be extremely dangerous when taken irresponsibly and without indication. Millions of men, women and children around the world are “drugging” themselves daily with soy products, and the tragic irony is that this is done in the name of “health”.

Keep in mind that tofu, tempeh and soy milk are not the only sources of soy. In fact, almost all processed food has soy in it, in the form of soy oil, soy lecithin, soy flour or soy protein. Everything from your favorite corn chips to hamburger buns to mayonnaise is likely to contain a substantial amount of soy.

The most sensible approach, then, is to eliminate processed soy products from your diet and dramatically reduce or eliminate your consumption of processed food (of course there are many other reasons to do this – soy is just one).

A small amount of miso or natto or other fermented soy product as a condiment every now and then is probably not harmful. But those are not the soy products Americans tend to eat.

For more information about the dangers of soy products, please see my recent article called The Soy Ploy.

  1. I can’t help but wonder if these scientific studies about soy have all been funded by the dairy industry. I find it difficult believing every scientific result especially when one finds out, sometimes years later, who the financial backer was of the study. I’m sure we have all read or heard about this kind of thing happening.

  2. What about vitamins derived from non GMO soy (as Britt was asking)? If we choose to suppliment with them that is… should there still be a concern of phytoestrogens after all the processes involved in extracting one pure vitamin, however silly this may be?

  3. This is truly the best researched information I’ve read about how “soy” is causing all sorts of estrogen-like related problems in humans- Boy, just imagine if scientists and Kris for that matter, had put forth the same effort into finding out if maybe, since almost all soy comes from GMO produced soy beans, that just maybe, it’s the GMO base products we should be looking more closely into. Or, maybe if the argument is that GMO produced Round-Up ready corn (Monsanto), won’t harm humans then, the fact that it’s doused in Round Up to keep weeds at bay, may be the root of all evil which prevails. I just don’t know. Hmm- go on Kris, enlighten us with a bit more than a half-shake

  4. I have been regularly using a whey protein powder (containing soy lecithin) for the last 3 months to aid recovery in a marathon training programme and have been impressed by the results and how much quicker I seem to recover from hard training sessions. However, my breasts have increased in size dramatically (this is not a joke and is also not a good thing), are painful and I have had some very irregular menstruation problems. I have also been adding flax seed to my diet. Could this be the effect of a sudden increase of phytoestrogens in my diet?

    • I doubt the flax seed does anything for your issues, assuming you’re not eating abnormal amounts. Why not cut out the whey and see what happens? Very hard physical activity can sometimes cause menstruation issues, not sure that correlates with the increase in breast size though.

    • I can testify that a small amount of phytoestrogens (not even soy but other foods that contain lower amounts of them) create a complete disruption of my hormone system (all kinds of problems related to the menstruation) and even migraines (I´m 51 years old, by the way). All the problems stop as soon as I stop ingesting those substances. I´m talking here about a regular consumption of nuts, just a little alcohol, flax seed and flax oil, miso (just eating it two days in a row, once a day), tea tree oil through a toe nail, licorice, flavonoids, sage, etc. What is a mystery to me is that phytoestrogens are given with good results to women as a solution for menstrual problems and migraine (!).
      I wanted to add another aspect of soy consumption: I read somewhere that poor people in an African country who ate a lot of soy got a serious problem of zinc deficiency. It seems that the consumption of soy interferes with the absortion of zinc, with all its consequences.

  5. Is the soy in multivitamins (e.g. Pure Encapsulations Nutrient 950 w/ vit K2) a concern?
    I do my best to stay away since it is a gluten cross reactive food that I am sensitive to.


  6. Well, very interesting. However, it is true. How to come out the population of China growing?
    Maybe, the ‘missing’ sperm is too weak and ‘they’ could not help human to extend their generation. So, it does not matter they exist or not. Producing a child just needs one strong sperm and a fine ovum.  😛

  7. That’s a good question, MJS.  It is true that the Japanese and other Asian cultures have eaten soy for millennia.  But there are two important things to understand about how soy was traditionally consumed in Asia.

    First, soy was almost always eaten fermented.  Soy was first used as a food during the late Chou dynasty (1134-246 BC), only after the Chinese learned to ferment soy beans to make foods like tempeh, natto and tamari.  Fermentation breaks down the phytates present in soy which inhibit nutrient absorption and protein digestion.

    Second, Asians eat very little soy when compared to Americans.  The average consumption of soy foods in Japan and China is 10 grams (about 2 teaspoons) per day.  Asians consume soy foods in small amounts as a condiment, and not as a replacement for animal foods.

    In the US people eat and drink vast quantities of unfermented soy products.  A vegetarian may have 1-2 cups of soymilk, 1-3 servings of tofu or soy-based “meat subsitute” and perhaps even one or more servings of soy “cheese” or “yogurt” in a day.  Furthermore, soy lecithin, soy protein, soy oil and/or soy flour are in just about every packaged food sold in stores – including so-called “health foods”.  Read the labels and you will see what I mean.

    Therefore, the average American’s soy consumption is many times higher than what was traditionally consumed in Asian cultures, and it is consumed in a much less healthy form (unfermented and highly processed).  That’s why it’s causing so many health problems.

    For more information about the dangers of soy, see The Soy Ploy on my blog and Soy Alert! on the Weston A Price Foundation website.

    • Chris, I normally respect your opinion highly, but this is clearly not true. Your statistics quote having half a serving of soy as sperm inhibiting, yet traditional Chinese and Japanese dishes very often use this quantity of soy in their dishes in the form of tofu. I don’t know where you got the two teaspoon number, but it is incorrect. You can visit Taiwan, or Japan and see it is untrue by having a traditional meal: tofu is eaten very often. It is unfair to post such a strongly worded article on one study, when you didn’t tell us if it was a double blind study? Control groups? Demographics seem to imply the study was flawed.

  8. Well, what about all the Pacific island nations where soy has traditionally been consumed all the time?   By this reasoning, shouldn’t there be no Japanese at all? Seriously, what is the explanation?

  9. @Just Say Georgia:

    I agree 100% that stress and our current lifestyle are a major cause of illness and dysfunction. However, I can tell you that plenty of “hippies” have fertility problems. In our acupuncture clinic I frequently see patients that have a number of problems, including infertility, with a diet high in soy. Once we get them to eliminate soy, and boost intake of egg yolks, organ meats, cod liver oil and other foods high in A, D, K, cholesterol and saturated fat, they do very well.

  10. How many ‘hippies’ have fertility problems? How many ‘hippies’ are vegetarians? I don’t know vegetarians who have fertility problems, I know overworked, overstressed, under-satisfied A-type professionals who have fertility problems. I’m telling you: take a vacation, ditch all devices, throw away the clocks and watches, take a break from the crazy world we’ve attached ourselves to and watch fertility bloom.