While there are those out there who continue to praise soy as some kind of miracle food, evidence continues to emerge which exposes its many faults and raises questions about its safety. 

Soy and other foods and herbs with estrogen-mimicking properties are often recommended to menopausal and post-menopausal women because high consumption may lead to amelioration of some of the symptoms associated with the natural decline in estrogen levels. They are also sometimes included in protocols designed to reduce the effects of excess estrogen in women with “estrogen dominance” and elevated levels of the estrogen fractions associated with higher rates of breast cancer. Phytoestrogens bind to estrogen receptors in the human body, thereby blocking the binding of the body’s natural estrogen. And since these plant estrogens have a much milder effect than true estrogen, they are believed to help with some of the symptoms associated with excess estrogen. Soy seems to play both sides of the coin: it has estrogenic effects, but can also be used to lessen estrogenic effects. Head spinning yet? Perhaps this is why the results of studies looking at soy and female health are so mixed.

Soy is also touted as a good source of protein, because it is one of the only complete proteins among plant foods (meaning it contains all the essential amino acids; although like all legumes, it is low in methionine). However, what is often not mentioned in the same sentence when soy is being touted as a plant-based protein source is that soy is also notorious for interfering with digestion of the very protein it provides. Soy contains trypsin inhibitors—compounds that reduce the efficacy of digestive enzymes—and these hardy anti-nutrientswithstand a high level of processing, so they’re still present in most commercial soy foods.

While Asian diets—commonly cited for being more health-promoting than Western diets—do contain soy products, they are usually prepared by traditional fermentation methods that reduce the potency of the digestive inhibitors and anti-nutrients. Moreover, soy sauce, miso, natto, and edamame are consumed in small quantities, and sometimes only as a garnish. Soy consumption in Asia is a world apart—no pun intended—from soy consumption in the modern United States, where vegetarians and vegans following plant-based diets can sometimes be better referred to as “soytarians.” They consume unprecedented amounts of soy, largely in the form of highly refined, puffed, extruded, and otherwise processed foods, such as soy milk, soy-based breakfast cereal, soy “chicken,” soy “cheese,” textured vegetable protein, and other soy-based foods marketed as imitation meat and dairy products.

Adults who have made a deliberate decision to consume a lot of soy aren’t the only ones affected by soy’s potentially adverse effects. With 25% of infant formula in the U.S. being soy-based, developing babies can be unwitting participants in an experiment that may have negative consequences for their long-term health. 

A recent study sheds light on a possible connection between increased seizure rates in autistic children fed soy formula, as compared to those fed dairy formulas. The author also found an association between soy formula consumption and epilepsy. The study identified a comorbidity of autism and epilepsy of 1.6–3.8%, which is higher than in the general population. Within that, among soy-fed infants there was a 3.6% rate of epilepsy, which is over twice as high as the 1.7% among non-soy fed infants. These numbers might seem very small, but as the author points out, “These may be considered by some readers as small percentages in each group who had seizures, but the two-fold or greater differences between soy and non-soy diets are statistically significant. Pharmaceutical interventions that reduced the incidence of febrile seizures or epilepsy by 2-fold would be in demand.” 

It’s important to note that these were associations, and they do not necessarily imply causality. However, similar findings relate soy consumption to seizures in other populations, as shown in an animal model of neurological diseases. Nevertheless, although the study was small and retrospective, it raises concerns which, when combined with other studies that sound the alarm, suggest people should be more cautious when ingesting large amounts of soy products that may have adverse effects on the body’s endocrine and neurological functions—particularly in populations as vulnerable as developing infants.

For more information check out the Whole Soy Story