Q: Is eating unfermented soy products bad for you?
A: So far there’s been little evidence that fermented soy products, such as tempeh, offer any advantage to healthy individuals over unfermented items, such as soybeans and tofu. Conversely, no research has yet proved that unfermented soy products are dangerous.
Some people reason that fermented soy is easier to absorb, and if a person suffers an intestinal disorder that has wiped out their normal gut flora, this may be true. However, a recent study at Tufts University (American Journal of Clinical Nutrition, 2003, vol. 77, no. 6) has shown that it doesn’t matter whether a person eats fermented or unfermented soy—the end results (as measured by blood levels of the active compounds) are the same.
Some people are concerned about eating soy because it contains substances that could potentially block the absorption of minerals and proteins. These substances include phytic acid and trypsin inhibitors. Although phytic acid can bind calcium, iron, zinc, and other minerals, the studies I’ve seen indicate that a person would have to eat huge amounts of soy before this would be a problem. On the other hand, several studies have shown that phytic acid has potent anticancer and immune-stimulating properties. If you have reason to be concerned about mineral deficiencies, it’s probably best not to take mineral supplements at the same time that you eat a soy product.
All soy products are heat-treated, which destroys most trypsin-inhibitor activity. For that reason, I don’t recommend eating uncooked soybeans.
This ASK THE EXPERT is written by Robert Rountree, MD, medical editor of Delicious Living.