Updated: Aug 21
Soy products are known as a wholesome food for the health conscious and tofu is especially popular among vegetarians as an easy replacement for animal protein. However, the soybean has a less-known, dark side, as it is armed with powerful anti-nutrients to protect itself from being eaten. These toxic substances disrupt body functions and weaken human health.
First is phytic acid, which blocks the absorption of minerals such as calcium, magnesium and zinc by forming non-dissolving phytates. Taking soy products often can lead to mineral deficiency and the many health problems that go with it.
However, there is an exception. The natural fermentation of soy products such as tamari and shoyu (soy sauce) as well as miso (soy paste) breaks down the phytic acid. Such soy products contribute to good health.
Another harmful anti-nutrient in soy is a protease inhibitor, which stops the enzyme-based breakdown of protein into amino acids. The body can benefit from protein only after enzyme activity splits protein into amino acids.
Even though soybeans are rich in protein, it is only fully available to the body when broken down. Fermentation dissolves the protease inhibitor as it does phytic acid.
The best known of the anti-nutrients in soybeans are the phyto-estrogens, which mimic the effects of the female hormone estrogen in the body. This upsets the hormonal balance of men and women, as well as boys and girls. Experts still debate the role of phyto-estrogens as a factor in breast cancer.
This most common female cancer is often hormone-related, whether from birth control pills or hormone replacement therapy in menopause. Another concern is the growing environmental contamination of food and water from the xeno-estrogens in plastic and other synthetic products that disrupt the endocrine system.
The soy debate shows the limits of science in proving anything. There is research that supports the arguments both for and against consuming soy. Some researchers believe that phyto-estrogens prevent breast cancer by occupying the estrogen receptors in breast tissue.
According to this theory, when soy estrogen locks on to the estrogen receptors in the breast, the body’s own stronger estrogen can’t go there to overstimulate breast tissue and trigger cancer. Other researchers maintain the opposite, namely that soy phyto-estrogens themselves are strong enough to trigger cancer. These experts recommend avoiding soy to reduce the risk of breast cancer.
The debate goes on, but the anti-soy researchers seem to make a stronger case. Moreover, apart from the breast cancer issue, phyto-estrogens suppress thyroid function and can cause autoimmune disease of the thyroid gland.
Even though fermentation doesn’t break down the phyto-estrogens, they aren’t a problem in small amounts as seasonings such as tamari or miso. Tempeh is a solid block normally made from fermented soybeans, but the short 24-hour fermentation time doesn’t give the same benefit as the long-term fermentation of tamari and miso. The good news is that tempeh is now available made from chickpeas, peas and other beans, so there is an alternative to soy-based tempeh.
In any case, it is wise for everyone, especially vegetarians, to limit the consumption of unfermented soy products, whether tofu, soy milk or soy meat substitutes. Highly processed soy protein isolate and other such soy products are the most harmful. Read labels on the food package to find the processed soy concoctions that the food industry adds to many foods sold on supermarket shelves.