Alex Poplawsky, Editor
Originally published September 2007.
Tofu can take on any form, fit or flavor. From soy burgers, sausage and jerky to scrambled eggs, smoothies and cheese, it is becoming apparent that any culinary desire is just an extrusion away. The consumption of such soy derived products is increasing for Americans, possibly due to recent reports on the health benefits of this alternative diet. But how does this dietary change impact the brain? With the knowledge of phytoestrogens in soy products, a heated debate has sparked concerns regarding the risk/benefit balance of tofu to health. To fully understand the controversies surrounding tofu, we must go back to the beginning…
Although the time or method of tofu discovery is largely unknown, it is believed to have arrived two millennia ago on the China scene. The most popular story attributes King Liu An (179-122 BC) to the birth of tofu. However, modern historians believe Liu An’s involvement to be simply honorary, since achievements were often given to ancient figures during the period when the Chinese word for tofu (doufu) first appeared in 950 AD. Other theories place tofu as an adaptation of the cheese making technology that migrated from either India or Mongolia, which were both dairy consuming cultures, unlike China, at the time. The Mongolian word for cultured milk products (rufu) serves as etymological evidence of this migration. The Chinese characters to signify these Mongolian sounds represent “milk” (ru-) and “spoiled” (-fu), while later substituting “soy” (dou-) to represent “spoiled soy”. Finally, there is the “accidental coagulation theory”, which considers that early consumers of a soy porridge may have used nigari, a magnesium chloride byproduct of refining sea salt, to flavor their meal. Nigari is still a popular denaturant used today to separate soy milk into curds and whey. By 1182, tofu arrived in Japan by way of Buddhist monks, whose vegetarian diets utilized tofu as their major source of protein. Only by the Japanese did it become known as tofu.
Beyond the origins of tofu, soy products are increasing their grip on the beef eaters of Western culture. The call for diets lower in saturated fats or views on meat independent meals have attracted the attention of heart watchers and hippies alike to focus their feastings around alternative protein sources such as tofu. There is even evidence to support that the phytoestrogens found in soy products could inhibit a class of kinases that are implicated in the proliferation of tumor cells. Under this label, phytoestrogen supplements are claiming to have protective properties against prostate and breast cancers. Although these views are beneficial toward the periphery, in a neurocentric world, there is still heavy debate concerning its effects on the brain.
Phytoestrogens belong to a class of isoflavones that are found in soy products and are chemically related to estrogen. In fact, soy phytoestrogens bind to the estrogen receptor (ER) and predominantly disrupt this endocrine. Also, phytoestrogens have a greater binding affinity for the ERβ compared to the ERα subtype. To make things even more complicated, these individual ER subtypes are dominant in different brain regions, and vary between the sexes and the phase of organism development. This means that phytoestrogens will have a different effect on the brain depending on the sex, how much, how long, and how old the subject is when soy is consumed. No wonder there is such debate among scientists!
Considering these complexities, a number of studies have explored phytoestrogen and the adult brain. One study administered a commercial phytoestrogen supplement to female rats and observed a decline in their sexual behavior. Adult male rats fed a routine diet that contained phytoestrogens displayed behaviors of increased anxiety and contained higher levels of stress hormones, like corticosterone, in their blood. Finally, it is traditionally observed that male rats regularly outperform females in visual spatial tasks. However, when fed a phytoestrogen rich diet, this dimorphism is reversed whereby the females regularly outperform the males and never ask for directions.
In addition to examining adult animals, there is an increasing interest in the effects of phytoestrogen exposure during the neonatal and early postnatal periods of human life when a grand orchestration of endocrines is performed to ensure proper brain maturation. Unfortunately, to this day, there is not a single widely accepted study of these time periods. What is known, however, is that phytoestrogens do infiltrate the placental barrier and are found in similar concentrations in the fetal brain as in the mother’s. Also, with 25% of total baby formula sales belonging to soy formula, a typical daily consumption of phytoestrogens for an infant is about 4 to 7-fold higher than the FDA recommendation for adults. This translates to a phytoestrogen blood concentration that is >10,000-fold above that of endogenous estrogen, which is comparable to doses found in animal studies! Whether this will have adverse effect on young humans is still under investigation.
Originating in ancient China, tofu has an upbringing that is cloaked by many questions. Even thousands of years later, few answers are left credible by the growing mystery of health and soy foods. The enigmas continue to mount with the uncertainty of what I had for dinner last night. Was that edamame flavored tofu?