I’ve been testing my brain function daily for the last six years. I use a reaction-time test (see digit, type digit as fast as possible) that takes about five minutes. I have gradually improved the test over the years — this is about version 8. One reason for this testing is that I might observe a sudden change. That could suggest a new factor that affects brain function — whatever was unusual before the change (e.g., a new food). This is how I discovered the effect of butter. My score suddenly improved, I investigated. Another sudden change (improvement) happened soon after I switched from Chinese flaxseed oil to American flaxseed oil. I hadn’t realized that something was wrong with the Chinese flaxseed oil. I started brain tracking after I noticed a sudden improvement in balance the morning after I swallowed about five flaxseed oil capsules. Millions of people had taken flaxseed oil capsules, but no one, it seemed, had noticed the balance improvement. Maybe other big changes in brain function go unnoticed, I thought.
A month ago, my score suddenly got worse (= I became slower). There was one unusual thing that day, before the test: I had eaten a piece of bai fu ru, a kind of fermented tofu popular in China. To make it, “cubes of tofu are first fermented, then soaked in brines that contain a number of ingredients: rice wine, vinegar, chili peppers, cinnamon, star anise, and red yeast rice, the last which imparts the deep red hue that you’ll see in certain varieties.” Here is a discussion of fermented tofu in Los Angeles. It’s popular in China. Most people use it as a condiment, but I ate small amounts (one cube) alone.
To find out if the bai fu ru caused the worsening, I did a test. I deliberately ate one 20 g cube at 11 am. I do the brain tests in the afternoon, usually 4-5 pm. What happen to my brain score that day? Here are the results.
Each point is a different test. I conclude that the tofu slowed me down by about 20 ms and the effect lasted two days. I didn’t notice the change in other ways — I didn’t feel tired or slow, for example. Presumably that is why this has gone unnoticed.
I think these results reflect cause and effect for several reasons:
1. Clarity. A t value would be very large.
2. Surprising prediction. A surprising prediction turned out to be true. Sharp drops like this are rare. Perhaps they happen once every 3-6 months.
3. Repetition. A research assistant found similar results, although not as clear. She is Chinese — quite different genetically.
4. Other evidence that tofu is bad for the brain. After I found these results, I remembered an old study. It found an association between midlife tofu consumption and late life cognitive decline among Japanese-American men in Hawaii (more tofu, more decline). A related study of the same men found a correlation between cognitive decline and miso consumption. A later study of Indonesian men and women also found a correlation between tofu consumption and cognitive decline (more tofu, more decline). The same study also found a beneficial weak correlation between tempeh consumption and cognitive decline (more tempeh, less decline). A weak epidemiological association found only once means little — epidemiologists, in my experience, do not adjust for the number of tests done and usually ignore the problem. More recently, an experiment using a mouse model of Alzheimer’s disease found that a high-soy diet made brain function worse.
Because of the other evidence, I conclude that all tofu (and other soybean foods, such as soy milk) probably impair brain function, not just this version, which contains slightly more than tofu. The other evidence involves lots of non-fermented tofu. Because of the other evidence and my assistant’s results, I believe these results will be true for other people.
I can’t explain the effect. Tofu is high in omega-6, but the amount of omega-6 in 20 g of tofu is small. Others think that tofu impair brain function due to its isoflavones.
Most nutrition experts say tofu is good for you. Catherine Newman, in O Magazine, raves about it. “In addition to being wonderfully inexpensive, tofu is high in protein, low in fat, and very low in saturated fat. . . . One daily four-ounce [= 120 g] serving is an excellent addition to a healthy diet.” The Mind Health Report (October 2012) says tofu is good for the brain. “For vegetarians, good choices are tofu, beans and eggs.”
Better informed experts criticize soy but say fermented soy is good. Joseph Mercola wrote,”For centuries, Asian people have been consuming fermented soy products such as natto, tempeh, and soy sauce, and enjoying the health benefits.” The Weston Price Foundation website says a lot about the badness of soy but claims fermented soy is healthy. In an article about why unfermented soy is bad, the Healthy Home Economist says, “Please note that fermented soy in small, condimental amounts as practiced in traditional Asian cultures is fine for those who have healthy thyroid function [as I do -- Seth].” My 20 g dose was a small, condimental amount. John Robbins, author of The Food Revolution (2001), dismissed the association of tofu and dementia. He argued:
That’s not all we know. We know, for example, that dementia rates are lower in Asian countries (where soy intake is high) than in western countries. We know that the Japanese lifestyle (with its high soy intake) has long been associated with longer life span and better cognition in old age. And we know that Seventh Day Adventists, many of whom consume soyfoods their whole lives, have less dementia in old age than the general population. . . . A number of clinical studies have shown that soy and isoflavones from soy are actually beneficial for cognition. . . . . Having studied the literature, soy researchers Mark and Virginia Messina conclude that “there is no reason to believe that eating soyfoods is harmful to brain aging.” [Robbins failed to mention that Mark and Virginia Messina own a "nutrition consulting company specializing in soyfoods nutrition" -- Seth]
I don’t know when the Messinas said this. Maybe there was once “no reason” to think soyfoods bad for the brain, but there is now. The new evidence, epidemiology, and mouse evidence make a good case.
Here are two interesting things. 1. A very popular food is dangerous, maybe harmful. 2. Nutrition experts had claimed the opposite: the food is good for you. Even the better ones (Mercola, Weston Price Foundation) got it wrong, ignoring evidence (the epidemiology). It is a good example of experts overstating their understanding. The Shangri-La Diet is another example (every expert said sugar was fattening, I found it caused me to lose weight).
Even more interesting is the methodological implication. Anyone can do what I did, with any food. It’s easy, safe, cheap, and takes little time. The bad effects were large enough, and the method sensitive enough, that the bad effects were well above noise. And this is a non-trivial case. Tofu is popular.
We eat thousands of foods. We have millions of genotypes. We eat our food in millions of environments. Your genotype and environment affect how a food will affect you. So a good understanding of how foods affect us would seem to require thousands times millions times millions of tests. It is absurd to assume that anyone else (government, academia, industry) will do the necessary tests. They can’t begin to do the tests. In contrast to people doing a job (for example, people in government responsible for food safety) you have a much simpler problem: Is my food safe for me? You only care about one genotype (yours) and one context (yours) and you eat far fewer than thousands of foods. You can do good tests. You can test exactly what you eat in exactly the context you eat it. Compared to the present, where we extrapolate from epidemiology, animal tests, and the rare human experiment, the reduction in uncertainty and increase in generalizability is immense.
If you want to do experiments like this — test foods one by one — with my software (which requires Windows), please contact me. The tests require a training period of 1-2 months so that the scores during an experiment are roughly constant.