Benefits of Miso

Benefits of Miso:


Miso is a Japanese word that means "fermented beans." Miso is usually found in the form of a thick paste, and the beans used during fermentation are almost always soybeans. During the soybean fermentation process, grains like barley, rice, or buckwheat might be added to achieve a certain flavor or other desired attribute, but in most situations, soybeans serve as the basis for miso fermentation. (This basic role of soybeans in preparation of miso can sometimes be overlooked because many varieties of miso may take on the name of their added ingredients, like "barley miso" or "rice miso." Yet virtually all of these miso varieties will contain soybeans as a basic ingredient.)

It's worth noting that under some circumstances, you might hear the word "miso" being used to refer to fermentation of a food other than soybeans. A good example is "fish miso." In this case, the term "miso" is being used to refer to the process of fermentation rather than the food being fermented. "Fish miso" is a term used to describe fish that has been fermented using the same basic fermentation process that can be used to produce soy miso, barley miso, or rice miso.

This use of the word "miso" in relationship to fish is important, because it tells us something very special about the miso fermentation process. For many miso eaters, the magic of miso lies in the micro-organism used for its fermentation: Aspergillus oryzae. This micro-organism is a particular type of fungus (a filamentous fungus, also called a "mold") that plays a special role in Japanese and other Asian cuisines. Long before scientists had developed ways of identifying and naming fungi like Aspergillus, cultures in China and Japan had developed special methods of fermenting soybeans (and other foods) that were practical and could be reproduced (assuring that the same mold was used, even though this mold was not yet scientifically identified). "Koji" was the term used to describe the end result when foods were fermented in this special way.

When scientists eventually discovered that the Aspergillus fungus was the key micro-organism involved with koji fermentation, the word "koji" took on a second meaning. While remaining the name for the end-stage product, it also became the name for the Aspergillus fungus itself. Therefore, you can now hear the word "koji" being used to refer to end-products of Aspergillus fermentation like miso or sake or soy sauce, as well as to the Aspergillus mold itself. You can also hear the word "koji" being used to refer to a grain-based starter that is used in the production of the above foods (including soy miso). When "koji" is used to refer to this starter, Aspergillus mold has usually been added to rice that has been pre-soaked and pre-cooked. The result is of this Aspergillus-fermented rice is called "koji." For a second stage fermentation into miso, "koji" starter is then added to soybeans that have also been soaked and cooked, and the entire mixture is allowed to age and ferment into miso. As you can see, the word "koji" can take on a variety of meanings. But these different meanings tell us something important about miso, namely, the special role played by the Aspergillus fungus in its fermentation.

Despite this primary focus on Aspergillus mold in fermentation miso, other micro-organisms are sometimes used in addition to Aspergillus during miso fermentation. The fungus Zygosaccharomyces rouxii is one of these micro-organisms. Other fungi include Pichia guilliermondii, Clavispora lusitaniae, Absidia corymbifera, and Candida etchellsii. Bacteria may also be used in the fermentation process. In the case of Japanese fermented soy pastes, Tetragenococcus halophilus and Staphylococcus gallinarum are bacteria sometimes used in fermentation. In the case of Chinese fermented soy pastes, species of Bacillus bacteria are more commonly used.

The texture of miso is usually paste-like and relatively thick, along the lines of peanut butter. But the color and taste can vary widely, depending on many fermentation-related factors. In terms of color, the lightest color miso is usually white or beige. This lighter color is often due to inclusion of a large amount of white rice during the fermentation process. When the word "koji" is used to refer to a miso starter made from rice and Aspergillus, white miso is also sometimes described as containing a large amount of koji. (If the koji has been made from Aspergillus fermentation of roasted rice flour, it may become light brown in color, but is often still included in the category of white miso.)

Another factor contributing to lighter color of white miso is shorter fermentation time. White miso is usually fermented for a much shorter period of time than darker-colored miso. (In some cases, a white miso may be fermented for a time period as short as several weeks, while a dark miso might be fermented for many months or even several years.) In terms of taste, white miso is usually the sweetest variety of miso. Some people also consider it to be the most versatile for cooking since it lacks the stronger flavors found in darker varieties of miso. In Japanese, the name for white miso is "shiromiso." When a miso like white miso is made with a large amount of rice, you may also hear it being referred to as "kome miso," since "kome" is the word for rice in Japanese.

When soybeans are fermented together with barley, the result is usually a miso that is yellow (or very light brown) in color. Since the Japanese word "mugi" can be used to refer to the general category of cereal grains (including barley and wheat), you will sometimes hear yellow miso being referred to as "mugi miso." Sometimes a small amount of white rice is also included during fermentation of yellow miso. One very popular yellow miso is Saikyo miso, traditionally made in the south-central region of Japan (the Kansai region).

In terms of color, the next major category of miso is red miso, sometimes called "akamimso" since "aka" means "red" in Japanese. Red miso may actually be a very dark brown or reddish brown in color, and it's usually (but not always) more salty than white or yellow miso. If a red miso is actually a very dark reddish brown in color, the brownish color may be the result of soybeans having been steamed prior to fermentation. While barley, rice and other grains may be used in the production of red miso, it is usually characterized by a very high percentage of soybeans, and for this reason is sometimes referred to as "mame miso" (since "mame" means "bean" in Japanese).

Dark brown and red miso usually get their strong flavors from longer periods of fermentation. In some cases, fermentation or dark soy miso may involve three years or longer. For example, Hatcho miso made by the Hatcho Miso Company in Okazaki, Japan (Aichi prefecture) is fermented in 200-year-old vats over a period of three winters.

Remember that regardless of the many names you may hear for different varieties of miso, virtually all include soybeans as a basic ingredient.

Nutritional Benefits

Nutritional benefits of miso have been claimed by commercial enterprises and home cooks alike. Claims that miso is high in vitamin B12 have been contradicted in some studies. Some, especially proponents of healthful eating, suggest that miso can help treat radiation sickness, citing cases in Japan and Russia where people have been fed miso after the Chernobyl nuclear disaster and the atomic bombings of Hiroshima and Nagasaki. Notably, Japanese doctor Shinichiro Akizuki, director of Saint Francis Hospital in Nagasaki during World War II, theorized that miso helps protect against radiation sickness.

Some experts suggest that miso is a source of Lactobacillus acidophilus. Lecithin, a kind of phospholipid caused by fermentation, which is effective in the prevention of high blood pressure. However, miso is also relatively high in salt which can contribute to increased blood pressure in the small percentage of the population with sodium-sensitive pre-hypertension or hypertension. Based on the other results of double-blind controlled studies of sodium and hypertension, there is no definitive evidence that high sodium intake leads to negative clinical conditions such as hypertension in healthy persons. Clinical evidence indicates wide-population heterogeneity in response to sodium.

Health Benefits

In comparison to research on soybeans and their overall health benefits, research specific to miso is
much less common. In addition, research on miso is complicated by the fact that human intake of miso can be difficult to measure in isolation since miso is usually consumed as part of a soup, stir-fry, or other dish. (For example, when participants in a study provide information about their intake of miso soup and scientists analyze the nutritional and health benefits provided by miso, the outcome can be confusing since other foods contained in the miso soup like tofu or sea vegetables might also have been responsible for the nutritional and health benefits.) Still, as an overall observation, we believe that intake of soy miso shows a preponderance of health benefits and perhaps even stronger health benefits than soyfoods in general. We also suspect that these potentially stronger health benefits may be related to fermentation of soy miso by micro-organisms like the fungus Aspergillus.

Overall Nutrient Benefits
Soy miso is a very good source of manganese and a good source of zinc (both important mineral antioxidants). It is also a very good source of the minerals phosphorus and copper as well as a good source of protein and dietary fiber. In addition to these conventional nutrients, soy miso is also an important source of phytonutrient antioxidants including phenolic acids like ferulic, coumaric, syringic, vanillic, and kojic acid.

An especially interesting group of antioxidants in soy miso is the group of antioxidants related to miso fermentation. In several recent studies, the amount of some specific antioxidants in soy miso appears to increase when fermentation is carried out for a longer period of time. DDPH (2,2,-diphenyl-1-picrylhydrazyl) antioxidants appear to be one category of miso antioxidants that increase with prolonged fermentation. These particular free radical scavengers may be more plentiful in miso that has been fermented for many months - or even several years - in comparison to miso that has only been fermented for one to three months. food.

Like other soy-based foods, miso can provide us with a wide variety of phytonutrients. Many of these phytonutrients can function as antioxidants and anti-inflammatory substances. Due to differences in starting ingredients, micro-organisms used for fermentation, and total fermentation time, not all of the phytonutrients listed below are contained in all varieties of soy miso. But the list below provides a good overview of substances found in all forms of soy miso combined:
  • Flavonoids and Isoflavonoids
    • daidzein
    • genistein
    • malonylgenistin
    • malonyldaidzin
  • Phenolic Acids
    • Caffeic acid
    • Coumaric acid
    • Ferulic acid
    • Gallic acid
    • Sinapic acid
  • Phytoalexins
    • glyceollin I
    • glyceollin II
    • glyceollin III
  • Phytosterols
    • beta-sitosterol
    • beta-stigmasterol
    • campestrol
  • Proteins and Peptides
    • defensins
    • glycinin
    • conglycinin
    • lunacin
  • Saponins
    • soyasaponins (group A and group B)
    • soyasapogenols
Cardiovascular Benefits
Most of the heart-related research that we have seen on miso has involved population groups in Japan, and so it is difficult to say if these research findings also hold true for other population groups. In one large study involving 40,462 Japanese participants and lasting for more than 10 years, intake of miso was found to associated with decreased risk of one major type of stroke (cerebral infarct, or CI). This health benefit from miso held true despite miso also emerging as a major source of dietary salt in the study. These findings are fascinating, because ordinarily, a certain percentage of the Japanese population would be expected to be salt-sensitive and to have blood pressure undesirably increased by high intake of salt. Increase in blood pressure, in turn, would be expected to be a possible risk factor for CI. Yet miso was been found to lower risk of CI - a result that is unusual for a high-sodium food.

Animal studies have repeatedly shown this same result for miso versus table salt intake. Animals consuming a 2.3% table salt (sodium chloride) diet and animals consuming a 2.3% salt-from-miso diet have not experienced the same results. Salt-from-miso diets have not been found to raise blood pressure, even when they provide an equal amount of salt as high table salt diets. Researchers speculate that the difference may be related to a combination of factors, including soy proteins, peptides, isoflavones, and diverse antioxidants found in soy miso. In addition, researchers point to the potentially key role of fermentation in transforming soybean content and rendering it more capable of cardiovascular support. Further research is needed to clarify all of these issues.

Anti-Cancer Benefits
This area of soy miso research remains controversial. On the one hand, we know that soy miso contains the isoflavone genistein, and we know that dietary intake of genistein is associated with decreased risk of certain cancers, including prostate cancer. Yet at the same time, we also have studies on soy miso intake that show no association between prostate cancer risk and level of soy miso consumed.

Or, to take another controversial example: if individuals who consume daidzein (an isoflavone found in soyfoods and other types of food) have the right type of intestinal bacteria inside of their digestive tract, we know that they will end up having some of this dietary daidzein transformed by their intestinal bacteria into a related compound called equol. We also know that micro-organisms used to ferment soy miso (including many different strains of the fungus Aspergillus oryzae) are capable of turning daidzein into equol during miso fermentation. In this way, soy miso can end up containing equol even before we eat it!

This conversion of daidzein into equol by Aspergillus during miso fermentation was originally thought to have some reliable cancer-preventive benefits, but studies in this area have not reflected such a result. For example, in a study measuring risk of breast cancer among Japanese women, intake of miso soup was not found to reduce risk. Other studies have show a similar lack of risk reduction for colorectal cancer and prostate cancer based on intake of miso soup.

We have not seen any research studies specific to miso showing increased risk of cancer in any form. However, we are also unable to describe any clear anti-cancer benefits for soy miso based on the studies that we have seen. It's difficult for us to imagine negative consequences when taking a whole food like whole soybeans and allowing them undergo natural fermentation under safe conditions. We would expect a naturally fermented whole food to provide outstanding health benefits, including anti-cancer benefits.

However, soy miso is definitely a challenging food to research. As mentioned earlier in this section, consumption of miso can be difficult to measure in isolation since miso is usually consumed as part of a soup, stir-fry, or other dish. In addition, miso is often consumed in relatively small amounts in comparison with other foods. We hope that researchers will continue to investigate possible anti-cancer benefits from miso intake, and devote more attention to this uniquely fermented form of soy.

Digestive Benefits
In some ways, it's accurate to think about soy miso as a food that has been "pre-digested." That's because Aspergillus and other micro-organisms used in fermentation of soy miso can help metabolize proteins, carbohydrates, and fats found in soybeans and transform them into smaller molecules that may be more easily digested. In addition, depending on processing and fermentation methods, some soy miso can contain "friendly" bacteria like lactic acid bacteria (including various species of Lactobacillus) that might be helpful in supporting intestinal microflora. We have not seen large-scale, human research studies showing benefits of soy miso consumption for the digestive tract, but we would expect such studies to show digestive benefits based on the above factors. Hopefully, more attention will be given in future research studies to soy miso and its potential digestive benefits.

Fermented Soy Foods and Vitamin K
As described throughout this Health Benefits section, much of the nutrient support we get from fermented soy miso depends on the micro-organisms used in fermentation. While Aspergillus oryzae is often a premier micro-organism used in miso fermentation, other micro-organisms - including bacteria - can be highly important. Bacillus subtilis is one of these bacteria, and it is more commonly used in fermentation of Chinese miso than in Japanese, Korean, or Indonesian versions of this fermented soy food.

From a health standpoint, one of the reasons that Bacillus bacteria are so interesting is their ability to create a form of vitamin K called menaquinone-7 (MK-7). Vitamin K (in all forms) is an important nutrient for bone health. Sufficient intake of vitamin K is associated with decreased risk of osteoporosis, since this vitamin is involved with maintenance of bone mineral density and also with shaping of bone structure (through gamma-carboxylation). In the case of MK-7 (the form of vitamin K produced by Bacillus bacteria, and a member of the vitamin K2 menaquinone family), we know that higher levels of MK-7 in the blood correspond to lower risk of hip fracture in older Japanese women, and that higher MK-7 levels correspond to increased intake of soy foods that have been fermented with Bacillus bacteria.

One fascinating aspect of Bacillus-fermented soy foods is the potential ability of these bacteria to stay alive in our lower intestine after these foods are consumed. We've seen one study in which 1.6-20 million Bacillus bacteria (per gram of feces) were found to remain alive up to 6 days following consumption of natto. If Bacillus bacteria from fermented soy foods can remain alive in our digestive tract, they may keep providing us with vitamin K benefits many days after their consumption.

It's important to remember that Bacillus bacteria are not used in production of all miso, and it can be difficult to determine which miso products have been fermented with the help of these bacteria. (Sometimes a call to the manufacturer may still not result in a clear answer here.) Our recommendation here is that you consider selection of Chinese miso products if you want to enjoy miso in your meal plan and you are paying special attention to your vitamin K intake, since Chinese miso is more likely to have been fermented with Bacillus bacteria.

Consumption Tips

  • Miso is widely used as soup, which is both quick and easy to prepare. It can be eaten at any time and is healthy.
  • For preparing miso soup, heat miso paste and water at low medium heat. It can be eaten as it is or after adding some traditional fixings, like scallions, shiitake mushrooms, carrots, tofu, burdock, and daikon radish.
  • Miso sandwiches can also be prepared, by spreading miso paste on a slice of bread and topping it with tahini. Sliced avocado can also be added to it, to add taste.
  • Carry dried miso soup packets and enjoy them as a pick-me-up coffee substitute.
  • Miso can be used as an ingredient in marinades, for cooking meat, fish, poultry or game.
  • Miso, when combined with olive oil, flax seed oil, ginger and garlic, results in Asian-inspired dressing that can be used on salads or cold grain dishes.


Allergic Reactions to Miso
Although allergic reactions can occur to virtually any food, research studies on food allergy consistently report more problems with some foods than with others. For example, according to a recent report by the U.S. Centers for Disease Control, 90% of food allergies are associated with 8 food types: soy foods (such as miso), peanuts, fish, crustacean shellfish, wheat, cow's milk, hen's eggs, and tree nuts. (Crustacean shellfish include shrimp, prawns, lobster, and crab. Tree nuts include almonds, cashews, walnuts, pecans, pistachios, Brazil nuts, hazelnuts, and chestnuts.)

These foods do not need to be eaten in their pure, isolated form in order to trigger an adverse reaction. For example, yogurt made from cow's milk is also a common allergenic food, even though the cow's milk has been processed and fermented in order to make the yogurt. Ice cream made from cow's milk would be an equally good example.

Food allergy symptoms may sometimes be immediate and specific, and can include skin rash, hives, itching, and eczema; swelling of the lips, tongue, or throat; tingling in the mouth; wheezing or nasal congestion; trouble breathing; and dizziness or lightheadedness. But food allergy symptoms may also be much more general and delayed, and can include fatigue, depression, chronic headache, chronic bowel problems (such as diarrhea or constipation), and insomnia. Because most food allergy symptoms can be caused by a variety of other health problems, it is good practice to seek the help of a healthcare provider when evaluating the role of food allergies in your health.

In addition to the general allergy-related issues described above for soybean-containing foods, there is some research information specific to miso that is important to consider. First is the issue of protein P34. In some studies, this protein has been found to be one of the primary allergenic proteins in soy. However, at least one study on consumption of Korean miso has shown an undetectable level of protein P34 (with a detection level of 0.45 nanograms) in the miso, making fermented soybean paste a potentially less antigenic (allergy-causing) food than other forms of soy. This potentially reduced allergy risk from miso versus other soy foods makes sense to us. The fermentation process - especially over a period of time involving months or years - is likely to result in substantial modification of the proteins in soy, including potentially allergy-causing proteins like P34.

Some of the anti-cancer benefits of soy miso might be related to its potential strengthening of the immune system. (Weakened immune system function is a risk factor for many types of cancer.) Research studies show that during the soy miso fermentation process, there is significant potential for the creation of immuno-supportive substances. For example, we've seen a study in which soybeans fermented with the help of the bacterium Tetragenococcus halophilus showed the ability to increase T helper type immunity. Since immune system function often depends on a unique set of peptides (protein building blocks), transformation of soy proteins during fermentation is likely to provide the immune system with some helpful peptidesand eventually lowering our risk of cancer through added immune system support.

Miso and Thyroid Health
Along with the increasing presence of soy foods (such as miso) in grocery stores and on restaurant menus has come increasing controversy over soybeans and thyroid health. We're not surprised to find strong conflicting opinions in this area because scientific research on thyroid and soy is both complicated and inconclusive. We have written an extensive review of what we know - and what we don't know - about this important issue at this point. You find the article Soy Food and Thyroid Health here.

Miso and Acrylamide
When certain foods are cooked, their amino acids (protein building blocks) can interact with their simple sugars to form acrylamide. Acrylamide is a potentially toxic and potentially cancer-causing substance that can be naturally present in uncooked, raw foods in very small amounts, but can be formed in much large quantities in certain cooked foods. Grain-based coffee substitutes and fried potato chips are examples of foods that can contain high amounts of acrylamide. Even though you may find some websites listing miso as a high acrylamide food, we have not found any indexed journal research studies to support this finding. In fact, we have seen several studies on a related soy food - soy sauce - showing no detectable levels of acrylamide.

The absence of high acrylamide levels in soy miso makes sense to us, because traditionally prepared soy miso does not undergo any high-heat processing, and also because the sugar content of miso is relatively low when soybeans make up the bulk of the miso ingredients. (Cooked soybeans contain only 2-3 grams of per half cup of total sugars.) In addition, traditionally fermented miso should definitely not be classified as a processed food that is comparable to potato chips or a grain-based coffee substitute. It is a natural food based on whole soybeans and natural processing of these who soybeans by micro-organisms.

Infants and Miso
One study from Japan has shown that breast-fed infants already diagnosed with atopic dermatitis (an inflammatory skin condition) experienced a worsening of dermatitis symptoms when their mothers consumed miso soup and soy sauce. We aren't sure how this research finding applies to healthy Japanese breastfeeding infants, or of course, to infants who are breastfeeding in the U.S. However, the result here does remind us of the importance of considering food sensitivity in the feeding of infants, and the potential difference between individual concerns for infants versus adults involving soy foods, including miso.

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