Last month’s column focused on the health benefits and economic advantages of legumes. This month, I’d like to look at one particular legume and some concerns I have about the way it can negatively impact our health: the soybean.
Soy foods have been part of the American diet only for the past few decades, and we’re consuming them in ways quite different from our Asian counterparts. The most common uses of soy in Asian cuisine are as condiments — miso and both natural soy sauces tamari and shoyu. Tempeh and tofu are also consumed, but moderately and traditionally served with animal products.
In the U.S., we now eat large quantities of soy foods — mostly highly processed imitations of real food such as soy milk and soy burgers — and food items made from soy protein isolate, like soy cheese, soy “dogs” and soy bologna.
We also drink smoothies “enhanced” with soy protein powders and eat bread made with soy flour. And we do so because these items are being marketed as near miracle foods—perfect protein sources able to prevent or cure a host of diseases. In actuality, soy presents some cause for concern.
Soy contains several different anti-nutrients that are natural toxins, one of which inhibits the functioning of the pancreatic enzyme trypsin which is needed for protein digestion. Diets high in trypsin-blockers can produce gastric distress and chronic deficiencies in amino acid uptake. Put simply, they lower your ability to absorb protein.
All legumes have trypsin-blockers, but soy has a particularly high concentration. With other legumes, cooking neutralizes most of the toxins, but soy needs to be fermented in order to reduce them effectively. Fermented soy products include tempeh, miso, tamari and shoyu, but not tofu. The way tofu is made decreases trypsin-blockers, but it does not eliminate them the way fermentation does.
Another anti-nutrient found in soy is called phytic acid. This substance blocks the body’s absorption of essential minerals, including calcium, magnesium, copper, iron and zinc. It is present in the bran of all legumes, but long soaking and cooking times effectively neutralize these phytates. Again with soy, only fermentation can significantly reduce anti-nutrients, so a diet high in unfermented soy products can also lead to mineral deficiencies.
The negative health impact of soy foods don’t stop there. There are a growing number of doctors and scientists who are concerned about risks that soy foods pose to the human endocrine system, especially the thyroid gland.
Soy beans and soy products are goitrogens, which means they can disrupt thyroid function causing symptoms of hypothyroidism and goiter. In 1991, Japanese researchers found that as little as 30 milligrams of soybeans — about two tablespoons — given to human subjects daily for one month resulted in “significant” change in thyroid hormones. Half of the healthy people studied developed a small goiter and/or experienced symptoms of hypothyroidism such as fatigue, weight gain, migraines and insomnia.
Soy also contains phytoestrogens called isoflavones that resemble the hormone estrogen. Soy’s isoflavones have been linked to reproductive disorders including infertility. In 1992, the Swiss Health Service estimated that 100 grams of soy protein provided the estrogenic equivalent of the birth control pill. Think about it, the phytoestrogens in soy resemble the natural estrogens in our bodies.
What is going to happen to the balance of hormones in our bodies if we start adding more of one of them? How is the endocrine system going to handle the sudden increase?
This may not be an issue for people who grow up eating small amounts of traditionally prepared soy foods such as in Asian countries, but what about for Americans who start eating large amounts of soy as adults? And what does this mean for babies on soy formula and growing children? The effects will most certainly be different for different people.
This is not to say that all soy is always “bad.” Moderate amounts of fermented soy products can be a healthful part of a varied and balanced diet. Tofu can, too. Traditional foods are generally safe — they’ve been time tested. Recent inventions like soy salami and cereal made from soy flours are a different story. Since the FDA regulates only drugs, not food, no “safe dosage” levels exist.
As consumers, we need to look at advertisers’ claims with some healthy skepticism and to remember our best sources of information come from unbiased sources, not PR campaigns.
So have some tofu in your miso soup, sprinkle some tamari on your brown rice or have tempeh in a stir-fry, but you may want to skip the soy burgers and the soy protein powder smoothies.
Jennette Turner is a natural foods educator in the Twin Cities. Information about her workplace classes, private consultations and her online meal planning service, Dinner with Jennette, can be found at www.jennette-turner.com.