Tofu, Edamame & Soy Sauce Fine, But Soybean Oil Found To Be Harmful To Brain

January 31, 2020

There’s a great deal of controvery around the consumption of soy. It’s ubiquitous; found everywhere from the dinner plates of billions of people across the globe, to the bellies of countless farmed animals and fish, to biofuels, soaps and perhaps even the candle you’ve been burning this winter. Just like any other staple crop, it is essential, but not without its pitfalls.

Soy grows in a wide range of climates and terrains, including places that used to be the most lush, biodiverse rainforest on earth. This is unfortunate, because profits tend to take precedence over biodiversity, as you well know by now. Last year, experts forecasted a surge in the deforestation of the Amazon as a result of the US-China trade wars, and we’re already seeing this prediction come to pass. With the US now supplying far fewer soy beans to China and the demand only increasing, other key players like Brazil are now upping their supply, which means only further catastrophic degradation to the mighty lungs of the earth.

Environmental issues aside, there is much controversy surrounding the health benefits and trade-offs in men and women who consume soy. A glance at the scientific literature reveals much conflict, which tells me that we desperately need further investigation.

Soy contains phytoestrogenic isoflavones, meaning that consuming soy provides the body with compounds that mimic estrogen. It has been shown previously that early life exposure to these isoflavones in girls decreases estrogen receptor activity during puberty. Cast your mind back to cell bio and you might recall that receptors are compounds that sit on the cell membrane surface ready to cause certain chain reactions within the cell when they come into contact with their particular substrate of choice (here, estrogen). Estrogen signaling during puberty is critical for breast development and this study suggests that exposure to soy during this time may alter breast development and lead to a decreased sensitivity of breast tissue to circulating estrogen later in life. This is good, because excess circulating estrogen can increase one’s risk of developing breast cancer (though it’s a very complex issue with multiple genetic and environmental factors involved).

Another large scale study found that consumption of soy was found to have anti-cancer effects in a group of Chinese women. Soy has also been described as having anti-cancer potential in prostate cancer, so although there are fundamental sex differences, there appears to be potential benefits to all people. Furthermore, phytoestrogens (like soy) have been shown to have a protective effect on premenopausal women with Non-alcoholic Fatty Liver Disease (NAFLD).

It’s more complicated, though, and this is where it can get a little confusing about knowing what to believe. For example, this study found that while one of the isoflavones in soy decreased the risk of developing thyroid cancer in subjects, another increased it. This demonstrates the complexity involved in each unique, physiological system and why it’s important that we consider how risk factors differ from person to person.

Another potential detrimental impact of phytoestrogens are on the gut microbiome. It has been shown that organisms in our gut can synthesize phytoestrogens to more potent forms of the hormone and in some cases, cause dysbiosis, or the growth of more of the bad microorganisms and less of the good. With the growing pool of evidence linking the gut microbiome with changes in neurobehaviour via the gut-brain axis, consistent, high doses of phytoestrogens may lead to greater changes in behaviour later in life, manifesting in a variety of ways.

A fascinating area of research explores the way that phytoestrogens like soy change brain plasticity, or the ability of the brain to form new neural circuits (that have implications on everything from metabolism to social behavior). A brand new study from the UC Riverside has found that soybean oil causes genetic changes in the region of the brain linked to memory, metabolism, and the stress response. Among other things, detrimental changes in the hypothalamus can result in the likes of autism and Parkinson’s disease. The same team of researchers who found several years prior that soybean oil induces obesity, diabetes, and insulin resistance have just found further dysregulated genes resulting from soybean consumption. Some are associated with inflammation and hormone signaling pathways, including the gene coding for oxytocin—the “love” hormone that is vital in maternal bonding, as well as that between romantic partners.

The study was performed in male mice, so it’s uncertain whether female subjects would experience the same results. There’s a major issue of negligence of sex differences in scientific research. For example, it has been demonstrated previously in male mice that the consumption of phytoestrogens are important for plasticity in the hippocampus—another region of the brain. The hippocampus is associated with memory, among other things, and it was shown that male mice fed a phytoestrogen-free diet, showed decreased fear memory. Does this translate in females? It has also been shown that male mice fed a low-phyto diet for six weeks showed reduced sociability. Again, what about females?

Note that most of the research I have mentioned above tends to describe the positive benefits of phytoestrogen consumption. Honestly, that’s what appears to dominate in the scientific literature, which—as someone who indulges in tofu and the like—pleases me greatly! There’s even research describing the usefulness of phytoestrogens in improving skin’s elasticity. I’m not getting any younger, so these are things I like to think about.

What really stands out here is the negative effects of consuming soybean oil specifically. Tofu, soy sauce, and edamame all contain healthy fatty acids and proteins and little of that oil that has been found to impact those brain genes. The problem we face, however, is that soybean is the most abundant oil in our processed foods, so it’s hard to escape if pre-made things in packets contribute to your diet in any way, shape or form.

As with most things, I believe that ethical consumption of soy products in moderation is best. Try your best to avoid soybean oil, but don’t panic so much about the tofu and soy sauce. Just spare a though to where those beans originated; deforestation is a very real issue, as I highlighted earlier, so pay attention to the source that supplies yours. Oh, and the next time you buy those vegan patties or butter substitutes, have a read of the ingredients list and report back; soybean oil is everywhere.

What are your thoughts on soybean oil?


Photo: Vita Marija Murenaite on Unsplash
Kat Kennedy is an Arizona-based physiology doctoral student and holistic health advocate writing about science, health, and her experiences as a third culture kid and global nomad. She's @sphynxkennedy everywhere.


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