Soy is often advertised as a super healthy food, and these days, you can find it in products like soy milk, soy cream, tofu, soy burgers, and soy yogurt. However, these products typically contain unfermented soy, which might not be as good for your health as you think. On the other hand, fermented soy products like miso, tempeh, tamari, natto, and traditional soy sauce are okay in small amounts. But consuming large quantities of unfermented soy can be harmful.
Soy has high levels of phytic acid, a substance that binds to minerals in the digestive tract and removes them from the body. Many cereals and legumes also contain phytic acid, which is why vegetarians can sometimes suffer from mineral deficiencies, especially zinc. Techniques like soaking, fermenting, and sprouting can reduce phytic acid, but unfortunately, soy milk, soy protein, soy yogurt, and tofu are not processed using these methods.
Soy also contains trypsin inhibitors, which prevent protein breakdown and can cause serious stomach issues and chronic amino acid deficiencies. In lab animals, these inhibitors have been shown to cause pancreatic problems, including cancer.
Soy products like soy milk, soy protein, soy yogurt, and tofu are also heavily processed, involving heat and acidic or alkaline baths. This processing can denature the protein and sometimes contaminates the soy with aluminum. Additionally, soybeans are low in essential amino acids, including cysteine, methionine, and tryptophan.
Soy lacks vitamins A and D, which are crucial for the proper use of bean proteins. This may be why many Asian cultures combine soybeans with fish or fish broth. Soy contains high levels of phytoestrogens, hormone-like substances. Studies have shown that infants fed soy-based formulas absorb these substances at levels equivalent to several birth control pills, which can lead to long-term health issues. Plus, soy has no cholesterol, which is essential for the development of the brain and nervous system in children.
Isoflavones in soy can also disrupt thyroid function, which is vital for regulating metabolism. Furthermore, spray-dried soy sauce and other soy products can contain cancer-causing nitrites. During the manufacturing process, toxic substances like lysinoalanine can form. Phytoestrogens genistein and daidzein in soy mimic human estrogen and can disrupt hormonal functions, potentially leading to infertility and breast cancer. Consuming just two glasses of soy milk per day for a month can affect your menstrual cycle.
Soybeans also contain substances that cause red blood cells to clump together and inhibit growth. Lab animals fed soy protein isolate have shown enlarged organs and increased fatty acid deposits in their livers. This isolate is widely used in school lunches, diet beverages, baked goods, and fast food.
Researcher Kayla Daniel, who wrote “The Whole Soy Story,” has found numerous studies linking soy consumption to a range of health issues, including malnutrition, digestive problems, immune and thyroid disorders, reproductive issues, heart problems, and cancer.
Two senior toxicologists at the U.S. FDA, Daniel Sheehan and Daniel Doerge, opposed the promotion of health claims for soy. They highlighted evidence suggesting that certain isoflavones in soy are toxic to estrogen-sensitive tissues and the thyroid. They argued that the public may face potential risks from soy without adequate warnings.
While it’s often argued that soy has been consumed in Asia for thousands of years, it’s worth noting that Asians usually eat the whole soybean, often fermented, and in much smaller quantities—around 7-8 grams daily. In contrast, many Western vegetarians consume about 220 grams of soy per day. Small amounts of fermented soy don’t have the same negative effects as larger quantities of unfermented soy products like soy protein isolate, soy milk, soy oil, soy meat, and tofu. Examples of healthier, fermented soy products include tempeh, miso, natto, and soy sauce.
In a 2010 “Great Health Debate,” leading health experts discussed various diets and lifestyles. While opinions varied on vegetarian versus omnivorous diets, almost all experts, including the vegetarians, agreed that non-fermented soy is best avoided.
If you care about the environment, it’s also worth noting that soy is often grown in monocultures that destroy large areas of land, killing insects, small animals, and native plants.