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Miso Soup — Cancer-Fighting Probiotics in a Bowl


Miso soup - Dr. Axe

Miso is a salty paste made from fermented beans (usually soybeans) that has been a staple ingredient in the Japanese diet for thousands of years. It can also be made using certain grains, such as fermented barley, rice or oats, mixed with salt and a bacteria called koji — which results in a range of miso tastes, colors and uses. Miso is one of the best condiments to keep on hand, as it’s versatile in recipes and packed with some noteworthy health benefits.

Known in the Western world as the main ingredient used to make miso soup, time-honored miso paste has been used traditionally to help battle health conditions, including:

  • relieving fatigue
  • regulating digestive and intestinal functions
  • protecting against gastric ulcers
  • decreasing cholesterol and blood pressure levels
  • preventing inflammation
  • lowering risk for diseases associated with lifestyle factors, like cancers and heart disease

But Wait, How Can Miso Soup Be Healthy If It Contains Soy?

Soy is a controversial topic, and generally I am in the “no soy” camp. How come? Today, soy is touted as a “health food” that’s high in plant-based protein, and therefore it’s added to numerous processed products — especially things like packaged veggie burgers made with soy lecithin, soy milk, soy yogurt and so on. Of course, soy is also the main ingredient in soybean oil and soy protein powder (where it’s called “soy protein isolate”). But while some promote the benefits of soy, evidence shows that most forms of soy should be avoided.

What’s the problem with soy? Is soy bad for you, and hasn’t it been included in Asian diets for centuries? The majority of soy used today in commercially sold products is far from the type traditionally consumed in Japan and other parts of Asia. An extremely high percentage of all soy grown in the U.S. today — roughly 94 percent — is genetically modified (GMO) and is not harvested the same way as traditional soy was for generations; therefore, it doesn’t provide the same nutrition benefits or digestibility.

According to a 2013 report published in The Journal of Nutrition, the source of soybeans and the processing procedures used to make soy products are believed to be important aspects to consider — mainly because these have significant effects on the content of certain bioactive protein subunits and “antinutrients” found in soy. The same report also mentions the documented potential safety concerns with increased consumption of soy products.

Negative impacts of soy products have been observed in thyroid and reproductive functions as well as certain types of carcinogenesis. Overall, existing data regarding soy’s risks is somewhat inconsistent or inadequate still (which is why the topic continues to be debated hotly), but the health benefits of consuming soy protein or isolated soy products are not well supported at all.

What sets miso apart — and similarly natto and tempeh, two other soy products — is that they’re fermented sources of soy. When you ferment soybeans, you have a completely different product that yields a completely different set of available nutrients. Organically grown fermented soy products like miso, tempeh or natto are the only types of soy I recommend consuming for this reason.

Miso Nutrition Facts

One tablespoon of miso paste has roughly:

  • 34 calories
  • 2 grams protein
  • 1 gram fiber
  • 4.5 grams carbs
  • 1 gram sugar
  • 0.07 milligram copper (8 percent DV)
  • 0.146 milligram manganese (8 percent DV)
  • 5 milligrams vitamin K  (6 percent DV)
  • 0.44 milligram zinc (4 percent DV)
  • 27 milligrams phosphorus (4 percent DV)
  • 12.3 milligrams choline (3 percent DV)

The biggest benefit of miso is that it’s brimming with probiotics. Because miso is fermented, it’s filled with beneficial, live probiotic cultures that have many upsides. You can think of probiotics as the “good bacteria” that inhabit our gut environment and balance “bad bacteria” that we obtain from poor-quality foods, toxins in the environment, contaminated water, pollution and so on.

Probiotics can help boost immunity — just like toxins enter our system and make us sick, probiotic microscopic organisms take residence in our digestive tract and actually benefit us. According to a 2013 study by the Research Institute for Radiation Biology and Medicine at Hiroshima University in Japan, aside from containing probiotic cultures, miso is also a great source of numerous essential nutrients including “vitamins, microorganisms, salts, minerals, plant proteins, carbohydrates, and fat.”

Miso also contains both antioxidant compounds and certain antinutrients. While normally we hear the word antinutrients and think of grains, legumes, nuts and seeds that haven’t been properly prepared and, therefore, can potentially lower our nutrient absorption and interfere with digestion, some antinutrients can also be beneficial. In fact, another common name for antinutrients is “phytochemicals.”

What exactly are antinutrients? Various phytochemicals (also called “phytonutrients”) are built into nearly all plant foods and serve the purpose of protecting the plant’s survival, since they keep away certain predators like bugs or rodents. Phytonutrients are known to have cancer-fighting properties and can also help control blood pressure, cholesterol, inflammation and oxidative stress.

Many studies have shown that fermentation has positive effects on antinutrients, helping to reduce the types that block nutrient absorption and, therefore, releasing more beneficial vitamins and enzymes. Fermentation also makes digestion of grains and beans that are used to make miso easier.

A 2002 study conducted by The Department of Foods and Nutrition at Haryana Agricultural University of India found that fermentation of various foods including rice, whey, greens and tomatoes drastically reduced the contents of antinutrients including phytic acid and and trypsin inhibitors, while significantly improving the digestibility of both starch and protein molecules.

Miso soup - Dr. Axe

5 Benefits of Miso and Miso Soup

1. Provides Beneficial Probiotics

Because miso is fermented and contains live active cultures, you can think of it as acting similarly on our digestive system as yogurt. However, one of the benefits of fermented miso is that it contains no dairy and is a suitable source of beneficial probiotics for people with lactose intolerance or dairy sensitivities to foods like kefir, yogurt and cultured cheeses.

The probiotic bacteria found in fermented foods thrive in our gut microbiota, increasing our immunity and improving digestion. Probiotics are still being widely researched, but in recent years probiotics have been tied to health factors including:

  • enhanced digestion
  • improved immune function
  • lower incidences of allergies
  • better cognitive health
  • lower risk for obesity
  • mood regulation
  • appetite control and much more

2. Helps Improve Digestion

Eating miso in its most powerful, healing form — miso soup — is an easy way to improve digestion. Beneficial probiotics found in miso help combat digestive issues caused by an imbalance in gut bacteria, including constipation, diarrhea, gas, bloating and IBS. Probiotics are even beneficial for people suffering from serious conditions like food allergies, candida viruses, ulcerative colitis and leaky gut syndrome.

If you’ve been overdoing it on commercial dairy products, baked sugary foods, grains and farm-raised animal products, you can likely benefit from consuming plenty of probiotic-rich foods. Probiotics will help cleanse your system and are known for speeding up the body’s ability to heal from gut-related illnesses.

3. Has Positive Effects on Blood Pressure

Although miso is high in salt (sodium), it’s been linked to prevention of hypertension (high blood pressure) according to both epidemiological and experimental evidence. The researchers at Hiroshima University believe that the sodium in miso might behave differently compared with sodium chloride (NaCl) alone. These biological effects might be caused by longer fermentation periods of the soybeans, barley or rice grains above 180 days.

The study conducted at the Research Institute for Radiation Biology and Medicine found that systolic blood pressure in rats receiving 2.3 percent sodium chloride (NaCl) was significantly increased, but rats receiving the same amount of salt from miso did not experience these effects. The blood pressures of the rats on a diet of miso that was high in sodium did not increase despite their sodium intakes rising. Even though miso contains 2.3 percent salt, the rats’ blood pressures were as stable as those who were fed commercial diets containing only 0.3 percent salt.

Other similar studies done on animals have found that long-term miso soup drinking also halts blood pressure increases in mice with salt-induced hypertension or organ damage. It’s believed that this might be caused by a possible retardation of sodium absorption in the gastrointestinal tract or by the direct effects of nutrients in the miso soup made from soybeans. The decreases in blood pressure levels despite higher sodium intake were associated with decreases in cardiovascular risks and renal damage.

4. Has Anticancer Effects

Because miso provides immune-enhancing probiotics, vitamins and antioxidants including phenolic acids, ferulic, coumaric, syringic, vanillic, and kojic acid — it’s not surprising that it’s been linked to natural cancer prevention. Antioxidant content of miso seems to improve when it’s been fermented for many months or even for years.

The Hiroshima University study also found that miso can be beneficial for preventing radiation injury and cancerous tumor progression. Researchers discovered that miso with a longer fermentation time (ideally 180 days) increased healthy cell survival in mice following radiation treatment and prevented tumor growth. Dietary administration of 180-day fermented miso was shown to inhibit the development of cancerous colon cells in mice. Overall, the incidence of gastric tumors in rats given a control was higher than those given the 180-day fermented miso. Other research shows that miso is also effective in scavenging free radicals and suppressing mammary cancer tumors including lung tumors, breast tumors and liver tumors in mice.

The prolonged fermentation process appears to be very important for protection against cancer and radiation effects. Miso at three different fermentation stages was tested in another study (early-, medium- and long-term fermented miso) and administered to mice for one week before irradiation. Animal survival in the long-term fermented miso group was significantly prolonged as compared with the short-term fermented miso group.

5. Good Source of Nutrients — Including Copper, Manganese and Vitamin K

Like other top probiotic foods including sauerkraut, kimchi and kombucha, miso helps to activate certain enzymes found in beans and grains that allow you to absorb the available nutrients they provide more easily. These include copper, manganese, B vitamins, vitamin K and phosphorus.

Other physiological properties of soybeans, especially when fermented, include important phytochemicals including vegetable fiber, isoflavones, saponin and melanoidin. Miso is also a decent source of plant-based protein, with about 2 grams per tablespoon serving.

A Brief History of Miso

Miso has been consumed for generations in parts of Asia, and it’s still used on a daily basis in Japan as a flavor in miso soup and numerous solid foods. Considered an essential ingredient for Japanese cuisine, it gives miso soup its signature salty bite and healing properties. Today more than ever, miso is prized for its versatility in healthy cooking around the world. In the U.S., Europe and Australia, miso is growing in popularity — especially in the health food scene where it’s commonly used in salad dressings, marinades, broths, meat stocks, soups and sauces.

As a “nitrogen fixer,” soybeans are said to be easy plants to grow since they help maintain the fertility of soil. An old practice in Japan is to grow soybeans around the edge of a rice paddy because the two plants are believed to make good companions for one another; together they keep away insects and pests well.

Miso is traditionally made by combining cooked soybeans or other legumes with the bacteria (or mold) called koji (Aspergillus oryzae). Soybeans are the traditional ingredient of miso, but almost any legume can be used (barley, chickpeas, lentils and fava beans). Koji is typically grown on rice and is often available from Asian food markets in this form, if you ever want to try making your own homemade fermented miso and miso soup.

Miso comes in a wide variety of flavors because altering any step of the process — ingredients, ratio of ingredients, fermentation time — will affect the taste of the finished product. In Japan, differences in taste have become regional specialties, with some areas producing sweeter miso and some producing darker, saltier miso. Hacho miso is made using only soybeans, while natto miso is made using soybeans and benefit-rich ginger root together. Most other types are made using a combination of soybeans and grains.

Miso Recipe Ideas

Treat yourself to some simple, homemade miso soup every day to easily take advantage of the many benefits that come along with consuming more probiotics and various nutrients. Or get creative and drop a tablespoon of miso into your favorite homemade dressing, stock or sauces for some extra saltiness, tang and punch.

Keep in mind that although miso’s sodium doesn’t seem to pose the same risks as the kind found in most packaged foods, it is a pretty salty food (one teaspoon has about 200–300 milligrams of sodium on average), and a little bit goes a long way. Sometimes just one teaspoon can add enough flavor to your meal, but using 2–3 is okay when needed, too.

Just make sure you look for quality miso, the kind that’s organic (and made with fermented barley instead of soy, ideally). It’s also important to buy refrigerated miso that has been fermented for at least 180 days (and even up to 2 years) and contains all of its live bacterial cultures.

If you come across powdered miso or miso soup that hasn’t been stored in the refrigerated section of your grocery store, it won’t contain the same beneficial probiotics. And if you don’t make sure to buy certified organic miso, there’s a good chance you’re getting a product made with GMO soybeans (check for the USDA organic seal and words “certified organic” or “organic certified” on the label).

Interested in making your own homemade miso soup? Simple! Just drop one tablespoon of miso into boiling water and add some scallions along with your favorite nutrient-dense sea vegetables (such as nori or dulse). Want to take things a step further and make your very own miso from scratch? Here’s how:

Homemade Miso Recipe


  • 6 1/2 cups organic soybeans or another legume (such as chickpeas or lentils)
  • 8 1/2 cups koji
  • 2 cups and 11 tablespoons sea salt
  • water
  • a glass jar with lid (large and thoroughly sanitized)
  • a heavy weight to place on top of jar


1. Soak soybeans overnight before cooking. Rinse the soaked beans and cook them until very soft. After cooking, strain the soybeans and keep the water for later use.

2. Mash the cooked soybeans and place in a large mixing bowl. In a separate bowl, mix koji with 3 tablespoons plus 1 teaspoon salt and then dump the mixture into the bowl with soybeans. Combine all ingredients.

3. Take the water left over from cooking the soybeans and slowly add it to the soybean/koji mixture to achieve a good consistency. You want a consistency that can be formed into a tightly packed ball. If the ball cracks up or crumbles, the mixture is too dry, so keep adding more water slowly.

4. Roll the mixture into packed balls and place them in your jar. Pack them tightly to remove any excess air, and then press all the balls to form a flat sealed surface. Add the remaining salt to the surface and especially around the edges. Cover with a lid or heavy flat object with an added weight placed on top.

5. Let the miso sit for 180 days, up to one full year. Keep the jar in a room temperature/cool place, but not in the refrigerator or somewhere too warm in the sun. The warmer the environment, the quicker the fermentation process will happen. Check your miso regularly and remove any mold that might appear on the surface. When it’s done fermenting and tastes to your liking, store it in the refrigerator (it lasts for several years!).

Miso Possible Side Effects

You’ll get the most from miso when you consume it in small amounts. There are a few reasons why this is true: it can potentially cause allergies and comes along with soy risks. It’s also always a good idea to ease into using probiotics for those who are new to them.

If you know you have a soy allergy, definitely stay away from miso. On the plus side, as with gluten products, fermentation likely changes some of the chemical structure of the soybeans and makes it easier to digest for most people since it becomes less inflammatory.

Soy products have been tied to hormonal problems because soy naturally contains phytoestrogens, which are estrogen-mimickers in the body. It’s possible for soy to increase estrogen levels and raise the risk for conditions like breast cancer, cervical cancer, PCOS (polycystic ovary syndrome) and other hormone imbalance–related disorders, so more miso (or any soy product) is not necessarily going to be better. While fermented soy poses less of a risk than processed soy, and provides many other benefits, it’s still a good idea to consume only small amounts and to avoid all soy products if you have a known hormonal condition.

As far as introducing probiotic foods goes, it’s best to ease into consuming these for most people. This allows your gut environment to slowly adopt and can help prevent diarrhea or other issues that a small number of people can face when introducing probiotics. Monitor how you feel and consider only having one to two sources of probiotics a day at first until you become more used to their effects.

Final Thoughts on Miso Soup

  • While I generally don’t recommend soy products, miso soup is made from fermented soy, and that makes quite the difference.
  • In fact, miso soup provides beneficial probiotics, helps improve digestion, has positive effects on blood pressure, holds anticancer properties and is a good source of nutrients.
  • There many ways to enjoy miso soup, so try it today!

Read Next: Treating Candida with Fermented Vegetables

From the sound of it, you might think leaky gut only affects the digestive system, but in reality it can affect more. Because Leaky Gut is so common, and such an enigma, I’m offering a free webinar on all things leaky gut. Click here to learn more about the webinar.

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