Soy foods fall into two categories: fermented (e.g. tempeh, miso and natto) and non-fermented (e. g. tofu, soymilk, edamame soybeans and soy nuts). Despite their health benefits, sometimes soy gets a bad wrap. And here’s why:
Soy contains two anti-nutrients that are common among legume family: phytates and lectins. Phytates can interfere with the absorption of certain minerals and lectins can bind to the lining of your intestines and cause intestinal wall damage, but the negative effects of these anti-nutrients can be largely eliminated through the process of soaking, fermenting or cooking.
These preparation methods for both non-fermented products – such as soy milk and tofu –and fermented soy products such as tempeh, not only reduce anti-nutrients but also improve digestibility and mineral absorption.
But the fermentation process has an additional benefit too; it helps to support beneficial gut flora. That is, it helps populate the gut with beneficial bacteria that assist with everything from your immune system to mental health.
On the other hand, highly processed soy products, like veggie meats, sausages, deli slices and protein powders and bars, are sometimes made from a concentrated form of soy protein called “soy protein isolate” that is not easily digested and many times can be contaminated with hexane, a toxic solvent which is used to extract the protein from the soy. You can avoid soy protein that has been processed using hexane by purchasing certified organic products, but I would keep these soy products to a minimum.
Some of the soy cheeses contain partially-hydrogenated oils (trans fats) and trans fats should always be avoided.
See my post on Soy and Your Hormones for more information about how soy can affect your hormones.