I was recently asked to write a piece about soy products for a publication and thought that I would share my views on soy with my followers on this blog. The consumption of soy products has grown in popularity in Western societies in recent decades on the notion that soy is a healthy food. After all soy is eaten in numerous countries in Asia without ill effect. And I too jumped on the soy bandwagon in my 20s consuming soy milk instead of cows milk (and scouting out every other soy product under the sun). I still see a lot of clients in my nutritional practice who come to me initially consuming soy milk.
Here's the thing: traditional Asian societies only ever ate soy beans (which are technically a legume) that were very long fermented (i.e. for numerous days or weeks) eg miso, natto, tempeh, soy sauce or tamari (which is wheat-free soy sauce). This is because soy beans contain extremely high levels of phytates which wreak havoc on the body including creating nutritional deficiencies, gut permeability (leaky gut) and inhibiting certain digestive enzymes. Traditional societies discovered that only through a process of very long fermentation can the toxic levels of phytates in soy beans be reduced making soy beans more digestible. Small infrequent consumption of these traditionally long fermented soy bean products is ok for the average person who is not suffering from any digestive issues. However, eating large amounts of unfermented soybeans on a regular basis is not a good idea (eg soy milk, soy cheese, soy yogurt, tofu, edamame, soy flour).
Beyond the issue of phytates, soy has additional problems. Soy beans also contain phytoestrogens which adversely affect hormones and can lead to reproductive issues such as infertility. A study at the Harvard School of Public Health found that consuming just 1 cup per day of soy milk decreased sperm count, especially in men who were overweight or obese. Other studies found that phytoestrogens in soy may adversely effect male reproductive hormones and sperm capacitation (an important process sperm must go through after being ejeculated into the female reproductive tract). Soy phytoestrogens also have potentially harmful effects on women. A large review of 47 studies found that soy phytoestrogens reduced levels of LH and FSH, 2 hormones essential to fertility and reproductive health, and increased menstrual cycle length (source: Chris Kresser). I don't think it is coincidental that I see many vegetarian yoga practitioners who eat large amounts of tofu in their diet and are unable to fall pregnant. Studies show that fermenting soy decreases but does not completely eliminate phytoestrogens.
The research on soy is not however clear-cut. Some studies (like the ones mentioned above) show harm, while others show no harm. On this basis I take a highly precautionary approach. Given that soy is not essential to health, is not nutrient-dense, contains extremely high levels of phytates and that soy phytoestrogens may cause reproductive and endocrine problems, I would recommend avoiding unfermented soy entirely and only consume long-fermented soy products in small infrequent amounts. The table below sets out a quick summary.