Soy – Not So Fast

Soy has been used traditionally in China, Korea and Japan for thousands of years. As a legume high in both protein and fat, it yields numerous products, many of which are now part of large industries. Among the traditional products are the unfermented tofu and soy milk, and the fermented miso, soy sauce, tempeh, and natto. In the early days of the “health food movement”, mid to late 1970’s, these products were brought to the public’s attention by the Japanese macrobiotic movement, and became adopted as excellent additions to vegan and plant-based diets.

Since the late 1980s there has been a great deal of emphasis on using soy for the health issues of women. Curiously enough, that is also about the time that soybeans began to be genetically engineered. I always found this timing coincidence curious.

Soybeans are known to contain both phytoestrogens and goitrogens.
Effect on women

Phytoestrogens (genistein is one of them) are similar to the female hormone estrogen, and thus they can have both positive and adverse effects. They may diminish hot flashes in post-menopausal women; on the other hand, when taken by pregnant women, genisteins may adversely affect the reproductive system of their developing male and female embryos. They may also provoke the same effects as excessive estrogen, and encourage the growth of endometrial and breast tissue. Soy products are recommended against osteoporosis because the assumption is that, being estrogenic, they will have a positive effect on bone mineral density, although that does not mean that they prevent fractures.
Soy weakens the thyroid

The presence of goitrogens – substances that weaken the thyroid – in soy has been known for at least 30 years. I mentioned that in my book Food and Healing (Ballantine 1996), the first edition of which was published in 1986. This is an issue that is mostly overlooked in the great soy marketing push: soy does weaken the thyroid. For clients who come to me for consultation, if they have any thyroid issues, I will suggest that they completely avoid any kind of soy, with generally good results. In addition, as a legume, soy in its uncooked state contains substances called trypsin inhibitors, also called proteinase inhibitors. These substances interfere with the protein-digesting activity of the digestive enzymes trypsin and chymotrypsin. Animals fed raw soybean meal show reduced growth and extensive damage to the pancreas. Cooking helps eliminate most of the trypsin inhibitors.
Growth problems

Soy is also a source of phytic acid, or phytates. According to the Weston A. Price Foundation (, high levels of phytic acid in soy reduce assimilation of calcium, magnesium, copper, iron and zinc. High phytate diets have caused growth problems in children. Phytic acid in soy is not neutralized by ordinary preparation methods such as soaking, sprouting and long, slow cooking, but need to be neutralized by fermenting. Therefore, tofu and soy milk, which are unfermented, are poor food choices, both for children and adults. Miso, soy sauce, tempeh, and natto are better sources in this regard, but there still is the problem of goitrogens, which appear to be linked to the phytoestrogens in soy, the very substance that makes them desirable for those looking at women’s issues. Let’s remember also that allergies to soy are extremely common, especially among children.

At this time (in the first decade of the 21st Century), about 89% of the soy crop in the United States is GMO, or genetically engineered, most commonly to resist an herbicide. Studies on mice show that when fed GMO soy, there are unfavorable changes in the liver, pancreas, and testes of these laboratory animals. When these animals were switched off the GMO soybeans and fed the standard non-GMO soy, their organs returned to normal.
How to be safe with soy

To be safe, if you are using soy products, it’s essential that they be organic, non-GMO, and fermented, such as tempeh, natto, and soy sauce. I think it’s OK to use tofu here and there, mixed into stir-fries or other dishes, but not too much. I really don’t like soy milk as a dairy substitute; it’s just a white liquid, like milk is, but highly processed. Real homemade soy milk tastes like bean water, which it is. The commercial stuff has a lot of ingredients in it, including sweeteners – just read the label carefully. While I have met women who feel that their hot flashes have diminished from drinking soy milk, as a whole I would advise against unfermented commercial soy as a healthy food, because of all the other problems mentioned.

  • esther

    “Studies on mice show that when fed GMO soy, there are unfavorable changes in the liver, pancreas, and testes of these laboratory animals. When these animals were switched off the GMO soybeans and fed the standard non-GMO soy, their organs returned to normal.”

    I’ve heard this discussed before, but I haven’t been able to find a reputable source for this. Can you help me out by sharing your source? Thanks!