Phytic acid in soy: can we reduce it?
Soybeans are high in phytic acid, a substance that binds iron, zinc, calcium, and magnesium in the digestive tract. Your body absorbs less of those key minerals because the phytic acid essentially sticks to them and escorts them into your stool. In many foods, the phytate content is reduced by soaking, sprouting, fermentation, and ultimately cooking. However, soybean phytic acid is difficult to remove—you can soak and soak soybeans and still retain high levels of this antinutrient.
Home cooks are faced with a key question: Is there an effective way to reduce phytates in soy? Can we benefit in any way from the mineral content of soybeans?
A 1985 study in the Journal of Applied Bacteriology, Sutardi and Buckle tested the level of phytic acid in soybeans after different preparation steps. After soaking and boiling the soybeans, the researchers found that they retained almost 100% of this mineral inhibitor. They proceeded to steam the beans and found a 15% reduction. The levels were only significantly reduced when the researchers fermented the soybeans into tempeh.
Keep these results in mind when shopping for soy milk and tofu. Soybeans in soymilk are soaked, strained, and cooked. Tofu has an extra step: a coagulant is added. Both products retain almost 100% of the phytates according to the 1985 study. When you look at your tub of tofu and see that one of those 12-ounce tubs has about 100 milligrams of magnesium, keep in mind that you’ll only absorb about 10% of it. that magnesium. You would probably triple that absorption in a fermented soy product.
Home cooks do better if they learn fermentation techniques to prepare their soyfoods. Soy milk can be fermented by diligent home cooks. Traditionally fermented tempeh and miso are available at many health food stores. These soy preparations will allow you to benefit from mineral-rich soybeans.