Likely one of the most controversial “health” foods on the market, soy has been implicated in many things that may have you wanting to steer clear of large amounts of soy products. Soy isoflavones mimic estrogen in our bodies and research has shown that they can contribute to tumor growth in the breasts and uterus. In men, soy has been shown to lower testosterone levels and sex drive.
Soy also is one of the foods most likely to cause allergic reactions, and soybeans are high in phytic acid, which is known to block the body’s absorption of minerals such as calcium, zinc, magnesium and iron.
Soy estrogens can affect the hormonal development of children, causing developmental disturbances in their growing brains, reproductive systems, and thyroids. Soy infant formula contains large amounts of manganese, which has been linked to attention deficit disorder and neurotoxicity in infants.
Scientists are beginning to understand the many effects of soy on the human body. Like many things, used in moderation, there may be benefits. Used as a nutritional replacement, however, soy may cause more problems than it is claimed to solve. For those of you interested in soy as a source of nutrition, it has been shown that consuming fermented soy products, like tempeh, miso, and natto has a far less damaging effect with respect to the issues addressed above.
Some soy products are fermented, like tempeh, natto, some traditionally fermented soy sauce, and tamari.
The Whole Life Challenge makes a soy sauce exception for traditionally fermented tamari for two reasons. One is that it is wheat-free. Soy sauce is not a gluten-free product and wouldn't be allowed at the lifestyle level even if fermented.
Fermenting soy releases an enzyme that then reduces its phytate content (an "anti-nutrient"). The phytates contained in soy prevent you from absorbing nutrients in foods or digesting the carbohydrates and protein in soybeans.