Fermented soy products such as miso and tempeh fermented the old-fashioned way, the way they are in Asia are very healthy foods, as are most traditionally fermented foods (e.g.,
The processing of soy also makes it a less than desirable food item since the process involves chemicals, such as aluminum, high heat and pressure, robbing it of nutrients it may have had. The high temperature denatures the protein so that it is virtually useless as a protein source. Some people even refer to soy as an anti-nutrient since it contains protease inhibitors, phytates, saponins, isoflavones which interfere with nutrient digestion, mineral absorption, and the immune system.
Phytic acid, from the hull, is the part that blocks mineral absorption especially calcium, magnesium, copper, iron and zinc. Unfortunately, cooking soy does not deactivate the phytates like it does for other foods that are high in phytic acid. Other vitamins actually increase their requirements when soy is consumed, such as Vitamins E, K, D and B12.
Trypsin is an enzyme that is responsible for the breakdown of proteins and this action is blocked by soy. When proteins are not completely broken down they tend to putrefy in the gut leading to a host of GI symptoms. Research has also shown that when trypsin is continuously inhibited that the pancreas is prone to pathologies, including cancer.
Soy also contains a substance that promotes red blood cells to clot and together with trypsin, this dynamic duo has been shown to inhibit growth.
Fermenting soy products inactivates these harmful effects.