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Healthy Food and Nutrition Publications


Another Look at Soy

By Jennette Turner

It certainly is a healthy time for soybean products! Sales of soymilk, tofu, and protein powders are booming. Soy is being aggressively marketed as almost a miracle food- able to prevent or cure a host of diseases and provide people with the perfect source of protein. But we need to be conscious consumers. Advertising means that something is being sold. (And usually, the more a product is pushed, the less you need it. Witness the amount of money spent on advertising fast and processed foods vs, say, fresh produce.... I haven’t seen any “got kale?” ads, have you?... )  We need to look at advertisers’ claims with some healthy skepticism, realizing that our best sources of information come from unbiased sources.

Despite the media blitz pushing soyfoods as the answer to all of our health problems, there are a growing number of scientists who are concerned about the health risks of soy. Unfortunately, they don’t have the same marketers, and so news is leaking out more slowly. But, studies are being done, and many of them show that soy may not be the miracle food that it’s sponsors would like us to believe.

Soyfoods originated in Asia, and their use has developed over centuries. The most common uses of soy in Asian cuisine are as condiments- tamari, shoyu, miso and natto. Tempeh and tofu are also a part of the diet, consumed moderately and traditionally served at meals with animal products - soy has never been a substitute for meat.

Soyfoods have only been part of the American diet for the past few decades. How are we consuming soy- like Asians? Hardly. We’re eating large quantities of tofu, soymilk and highly processed foods made from soy protein isolate, like soy cheese, veggie burgers, and soy bologne. We’re also drinking smoothies with soy protein powders and eating bread made with soy flour.

Moderate amounts of traditional soyfoods may have some benefits for health. But large quantities, especially of highly processed non-foods like soy protein powders and imitation meats, have some pretty big risks, especially for people who are using it as their major source of protein.

Soy contains several different “anti-nutrients”, which are natural toxins. One of these inhibits the functioning of trypsin, a pancreatic enzyme needed for the digestion of proteins. Diets high in these trypsin blockers can produce gastric distress, reduced protein assimilation, and chronic deficiencies in amino acid uptake. Put simply, they can make you not be able to absorb protein.

All legumes have these trypsin- blockers, but soy has a particularly high concentration. And with other legumes, cooking can neutralize most of it, especially with long cooking times- (something to think about when relying on the speedy pressure cooker). Soy needs to be fermented in order to reduce the enzyme blockers effectively. What are fermented soy products? The traditional ones: Tempeh, miso, tamari and shoyu. The trypsin-blockers are somewhat lowered in tofu, too, even though it’s not fermented.

Another anti-nutrient found in soy is called “phytic acid”. This substance is present in the bran of all grains, legumes and nuts, and blocks the body’s absorption of essential minerals- calcium, magnesium, copper, iron and especially zinc. For other beans, grains and nuts, long soaking periods and long cooking times will effectively neutralize the phytates. With soy, however, only a long period of fermentation can significantly reduce them. There does seem to be a reduction in the effects of the tofu’s phytic acid, but only when it is eaten with meat.

What does this mean? That a diet high in unfermented soy products can lead to mineral deficiencies. And again, the people most at risk are vegetarians, and especially vegans, who aren’t taking in high mineral animal products.

The risks of soyfoods aren’t just about nutrients, however. Soy contains isoflavones that resemble the hormone estrogen. These are “called phyto-estrogens”” and they can mean trouble for our endocrine systems.

The most research has been done on soy’s isoflavones and the thyroid gland. The isoflavones in soy are sometimes known as “goitrogens”, which means that they interfere with thyroid function. In 1991 Japanese researchers found that as little as 30 mg. of soybeans (about 2 T. ) 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. What are the symptoms of hypothyroidism? low energy, fatigue, lethargy, constipation and lowered metabolism are the main ones. (Happily, all of the participants returned to their normal state of health within 1-3 months after the study was completed.) Many protein powders are “enhanced” with isoflavones, and so the risk for thyroid dysfunction increases with their use.

Soy’s isoflavones have been linked to infertility and other reproductive disorders as well as thyroid disease. Think about it- the phyto-estrogens in soy resemble the natural estrogens in our bodies, right? What’s 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? It may not be an issue for people who grow up eating small amounts of traditionally prepared soyfoods, like people in Asian countries, but what about for Americans who start eating large amounts of soy as adults?

In 1992, the Swiss health Service estimated that 100 grams of soy protein provided the estrogenic equivalent of the birth control Pill. (30 grams is about 2 tablespoons.) What does this mean for growing children- both boys and girls? For men? For women? For babies on soy formula? The effects will most certainly be different for different people. And since the FDA only regulates drugs, not food, no “safe dosage” levels exist.

But what about the Japanese? They eat soy and have fewer reproductive cancers than we do, which is often cited as a reason to eat more soy. But they also have higher rates of digestive and thyroid cancers, which have been directly linked to soy consumption. So we need to pay close attention and make sure we’re getting the whole story.

Soyfoods may not be the panacea they’re made out to be, but they’re not all negative, either. We can look to tradition as our guide on how to eat them. Moderate amounts of fermented soy products like miso, tamari, and tempeh can indeed be a healthful part of our diets. 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 not.

Eating foods prepared in traditional ways is also a good bet. Have small amounts of tofu in your miso soup, not a huge slice of tofu cheesecake. Sprinkle a little tamari on your brown rice, or have some tempeh in a stir-fry. But you may want to skip the soymilk and protein powder banana smoothie.

Jennette turner is a Natural Foods Educator in Minneapolis. She Teaches public and private classes, and offers individual nutrition consultations. Jennette launced Dinner with Jennette (, to make it easier for people to incorporate natural foods into their diets. she can be reached at / 612-374-6039

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