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Soy Brain Damage

December 23, 2010 Written by JP    [Font too small?]

The claim: Men who eat tofu run the risk of (literally) shrinking their brains! Says who? Well, one of the leading or, at least, loudest voices in the natural health community – who shall remain nameless. It’s hard to find any component of the modern food chain that inspires quite as much debate or hyperbole as soy. Detractors claim it can cause everything from cancer to severe hormonal disorders in both men and women. On the other hand, promoters point to select evidence that suggests that soy offers many of the benefits of hormonal replacement therapy without the well documented risks. Where does the truth lie? I submit that the best possible answer is likely found in the medical literature.

There is a tremendous amount of data available on the health effects of soy. The majority of the scientific evidence is in the form of animal and in-vitro experiments. In order to make this topic more manageable and pertinent, I’ve decided to omit that information. Everything you’ll read in today’s column is based on human data exclusively.

The kernel of this controversy can be traced back to the April 2000 edition of the Journal of the American College of Nutrition. A report issued by the National Institute of Aging examined the connection between tofu consumption and brain function and size in a group of 3,734 elderly men. The finding was that “higher midlife tofu consumption was independently associated with indicators of cognitive impairment and brain atrophy in late life”. However, these results generated concern by outside researchers who noted certain methodological issues in the study that may have influenced the findings. This led to follow-up commentary which urged that “it is premature to issue dietary recommendations about the risk of eating tofu” and “that the results should be interpreted more cautiously”. (1,2,3)

In 2008, new evidence emerged that seemed to support the conclusions of the original study from 2000. A group of 719 senior men and women were the subjects of the ’08 investigation. Memory testing and food frequency questionnaires were used to assess a potential link between soy products (tempe and tofu) and cognitive decline. Once again, tofu was linked to poorer cognitive performance. But tempe, a fermented soy food, was “independently related to better memory”. The researchers point out that both foods contain high levels of isoflavones or phytoestrogens. However, tempe also provides a meaningful quantity of folate which may be partially responsible for the noted benefits. (4)

The problem I found while investigating this issue is that several other inquiries have not come to similar conclusions. For instance, a publication in the October 2010 edition of the journal Brain Research discovered that both tempe and tofu actually improved memory recall in a group of seniors with an average age of 67. Older seniors, 80 years and up, did not exhibit the same benefit, but neither did they suffer any discernible consequences based on soy intake. (5)

Three recent trials examining the impact of soy supplements containing concentrated levels of isoflavones have similarly reported positive findings. One of the latest, presented in the January 2009 issue of Age and Ageing reveals that seniors given 100 mg/day of soy isoflavones over a 6 month period scored higher on various cognitive tests than those receiving a placebo. Another publication from that same year determined that supplementing with 116 mg of soy isoflavones daily for 12 weeks resulted in “enhanced cognitive processes which appear dependent on estrogen activation”. It’s important to note that compatible findings have been reported in trials involving older and younger men. (6,7,8)

Soy Isoflavones May Improve Spatial Working Memory in Healthy Men
Source: British Journal of Nutrition (2009), 102: 1348-1354 (link)

The so-called “soy brain threat” is far from being an issue that is resolved in the minds of many nutritional experts. It’s clear to me that a blanket statement about the harmful effects of soy on the male brain cannot be confidently made at this time. However there’s certainly reason for pause with respect to regular tofu consumption in men. More research in that arena is called for, to be sure. If there is, in fact, something neurotoxic in soy curd, we need to identify exactly what it is. It doesn’t appear to be the phytoestrogens contained therein. So where does this leave us? Generally speaking, I think soy foods should be eaten sparingly. The fermented varieties (miso, natto, soy yogurt, tempe) are probably better options from a digestive perspective and possibly beyond. Likewise, soy supplements ought only be used if there’s a good reason to do so – in select cases of hot flashes, prostate disease, etc. This isn’t just a more balanced point of view than most, but it’s also what I do in my own diet and recommend to my clients. (9,10,11,12,13)

Be well!


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Posted in Food and Drink, Men's Health, Nutrition

12 Comments & Updates to “Soy Brain Damage”

  1. anne h Says:

    Another great, informative and very interesting post!

  2. JP Says:

    Thank you, Anne! 🙂

    Be well!


  3. Iggy Dalrymple Says:

    Did the fear-monger have the name that sounds like a seafaring soft-drink?

  4. Mark Says:

    Would the last name contain anything similar to “soda pop”?

    Soy is so multi-purpose. Great article

  5. Paul F. Says:

    Hi JP,

    Your research brings up the benefits of consumption of soy isoflavone supplements used for prostate treatment without a risk of a negative effect on cognition!

    The British research is specific to benefits of soy isoflavone supplements, not tofu.

    In my opinion the gain in tranquility due to your clarification, will benefit those induced to doubt by the controversy, may contribute to make improvements in cognition too.

    Thank you for your contribution to help to clarify this controversy, which may be negative by dissuading older men to use soy isoflavone supplements that would improve their cognition and prostate health.

    I wish the unnamed source of panic information will get your input and reconsider the blanket negative statement applied by extension across the board to soy supplements not based on fermented soy.

    Great research!

    Thank you!


  6. JP Says:

    Thank you, Iggy and Mark! 🙂

    Be well!


  7. JP Says:

    Many thanks, Paul!

    Be well!


  8. Alex Audette Says:

    Perhaps the questions that the researchers should be asking is “What effect does GMO soy pose on cognition” and “What effect does Round-up pesticide residue have on cognition” Much of the soy produced in North America is unfortunately owned by Monasnto.
    Be Well.
    Alex Audette TCMP. R.Ac.

  9. Thomas Says:

    Dear JP,

    I readed some of your articles, and I appreciate yours observations. Congratulation for your website.

    According to what I learn, the “bad” stuff in soy appears to be only the phytates content. This is why, this much more safer and healthier to eat only the fermented one: tempeh, miso, natto.

    Regards from france


  10. Thomas Says:

    PS: sorry I made a mistake in my comment above: it’s not the phytates that are bad but the pytic acid. Actually, it’s the phytates that inhibit the last one and then are good in that way.

    Eat more food rich in phytate (preparation for beans etc) to lower the phytic acid content

  11. Alan Says:

    What I find biased about this article is the anti-tofu/soy studies were done with 719 and 3,734 people, but the pro soy studies you discussed were done with as little as 30 people and 150 at the most. It seems extremely biased to not mention that the anti-tofu/soy studies are stronger because of the amount of people studied.

  12. JP Says:

    Hi Alan,

    Thank you for expressing your concerns. I will attempt to address your primary point.

    It may seem counterintuitive, but the smaller studies are actually more meaningful from a scientific standpoint. The reason is that they’re controlled studies. The larger studies, while still important, are observational. Controlled studies are more expensive, hence the smaller number of participants, but also more reliable – because they’re not based on recollection.

    To be clear, I’m not a strong proponent of including soy in the average diet. On the other hand, I think many claims about soy (both pro and con) are often overblown and not supported by verifiable data.

    Be well!


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