In the United States rice has historically been considered as hypoallergenic and is commonly the only grain allowed on an elimination diet for allergy testing. However, it appears that rice-associated allergy occurs more frequently in those individuals who continually eat rice and rice products over extended periods. Moreover, since food allergies are usually an immune response to proteins, brown rice, which contains more protein than white rice, may be more likely to cause an allergic reaction in those who eat this grain on a daily basis. In Japan, where white rice is a basic part of the daily diet, rice allergies are much more prevalent than in the West. Scientists at Nagoya College of Nutrition, in Japan, discovered that incubating white rice with unheated miso decreases the soluble allergenic proteins without any significant change in the nutritionally important insoluble proteins. Miso's ability to reduce allergenic rice proteins is most effective when rice is incubated with misos that contain a large proportion of soybeans, such as Hatcho miso, soybean miso, and red miso.
Allergists now know that it is the complex proteins in foods that cause the body's immune system to trigger an immune response. Miso is known to contain proteolytic enzymes that degrade complex proteins, rendering them much less allergenic. As miso ferments, or ages, the enzymes supplied by the koji digest the proteins of the rice, barley, and soybeans (depending on what type of miso is being made) into less complex amino acids. Not only are these amino acids much less allergenic, but they are also much easier to digest and assimilate. In fact, "enzymatic digestion" of soy products has been used in Japan to make them hypoallergenic.
It is not uncommon for those with soy, rice, and barley allergies to not react to soy, rice, or barley misos. The reason for this is now clear. The allergenic soy, rice, and barley proteins are destroyed by the miso fermentation process. The reason scientists found misos with a high proportion of soybeans to be the most anti-allergenic is obvious given the fact that soybeans are high in protein, and therefore, the koji used to make these types of misos produces an abundance of proteolytic enzymes that are used to reduce the soy protein to amino acids. Moreover, the enzymes that drive complex biological reactions, such as protein digestion, have very specific chemical structures that are quite heat liable. The temperature used in standard cooking and possibly the lower temperatures used in miso pasteurization can cause minute changes in the molecular structure of enzymes rendering them useless in biological reactions. This explains why scientists have reported that "heat-treated" miso does not reduce the allergenic proteins in rice. This may also help lend credence to the growing preference for unpasteurized miso and the practice of not boiling miso soup that is made with unpasteurized miso.
Once you understand miso's hypoallergenic properties, its use as a food tenderizer and food "conditioner" is very apparent. For centuries, Japanese chefs have used miso marinades to tenderize fish, poultry, and meat. Miso's powerful enzymes break down the complex muscle and fat fibers of animal tissues and at the same time increase their ability to absorb flavors during the marinating and cooking process. For vegetarians this same principle can be applied to making plant foods much more digestible and much less allergenic. Foods that are high in protein and fiber, such as legumes and whole grains (particularly wheat), can cause allergic reactions and, more commonly, gastric distress unless their complex protein is denatured. However, simple cooking may not be enough, particularly for sensitive individuals. Simply adding unpasteurized "live" miso to a recipe can make a difference. For example, marinating tofu in miso marinade will make it more digestible, less allergenic, and more flavorful. There are several ways miso can be added to recipes to increase flavor, digestibility, and nutritional value while reducing food's ability to cause allergic reactions and digestive problems.
For decades, anecdotal references suggesting that unpasteurized miso contains important "living enzymes" had no scientific basis. However, like many of miso's medicinal properties, its remarkable ability to make some foods more acceptable to our immune and digestive systems, while improving their flavor and texture, is starting to be confirmed by the scientific community. In rural Japan, even today, miso is often eaten with grains and legumes. Although food combining is a modern concept, the point of view that some foods are best eaten together may not be such a new idea after all.