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.



Will Brink is the owner of the Brinkzone Blog. Will has over 15 years experience as a respected author, columnist and consultant, to the supplement, fitness, bodybuilding, and weight loss industry and has been extensively published. Will graduated from Harvard University with a concentration in the natural sciences, and is a consultant to major supplement, dairy, and pharmaceutical companies.


His often ground breaking articles can be found in publications such as Lets Live, Muscle Media 2000, MuscleMag International, The Life Extension Magazine, Muscle n Fitness, Inside Karate, Exercise For Men Only, Body International, Power, Oxygen, Penthouse, Women’s World and The Townsend Letter For Doctors.


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