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Humble miso soup may have saved lives when the atomic bomb was dropped on Nagasaki. Science now confirms miso prevents radiation injury. It may also prevent cancer and hypertension. Here's why you need at least one cup a day.
When the second atomic bomb was dropped on Nagasaki on August 9th, 1945, 21 healthcare workers were attending 70 tuberculosis patients in a hospital 1.4 km from ground zero. None of them suffered from acute radiation poisoning.
Dr. Tatuichiro Akizuki, a physician at the hospital, credited this miracle to the fact that everyone was consuming daily cups of miso soup garnished with wakame seaweed.
In a new comprehensive review of both epidemiological and experimental studies, Japanese researcher Hiromitsu Watanabe from the Research Institute for Radiation Biology and Medicine at Hiroshima University confirms the power of miso to prevent radiation injury.
His review also documents the ability of miso to prevent many forms of cancer (colon, liver, breast, lung and stomach), as well as hypertension.
Miso, or fermented soy bean paste, is a traditional staple of the Japanese diet. Soy beans are fermented with sea salt, koji (a mold starter), and sometimes rice, wheat, oats or other grain. The mixture is fermented for three months to three years.
The resulting enzyme-rich paste contains vitamins, microorganisms, salts, minerals, plant proteins, carbohydrates, and fat. But fermented foods are more than the sum of their ingredients. Fermentation gives rise to compounds that have amazing healing properties. Fermented foods like kimchi, natto, apple cider vinegar, and even wine and beer have been called "medical foods."
Watanabe's review of the science emphasizes the importance of traditional fermented foods like miso to prevent disease and maintain health. Here is just a brief sampling of his findings.
Miso Protects Against Radiation Injury
In a series of experimental studies, mice were fed a regular diet, or a regular diet with 10% dried red rice miso. After a week, the mice were subjected to radiation. The group fed miso had significantly greater numbers of surviving intestinal crypts – glands found in the epithelial lining of the small intestine and colon. Damage to crypts is believed to lead to colorectal cancer.
But when miso was fed to mice after radiation treatments, it didn't have the same effect. The researchers concluded that in order to reap the benefits, the blood must contain a certain concentration of the active compounds in miso before exposure to radiation.
The researchers believe miso's beneficial effect is closely related to substances produced during fermentation stages. They tested miso fermented for three to four days, 120 days and 180 days. Miso fermented for longer periods resulted in increased survival rates. Miso fermented for 180 days was considered most beneficial.
In other studies, miso fermented for 180 days significantly reduced tumor size and the number of tumors in the lungs of experimental rats.
Miso Prevents Breast Cancer
According to one epidemiological study, consuming a cup of miso three times a day reduced the occurrence of breast cancer. Tofu, natto, soybean and fried bean curd did not have the same effect.
In laboratory studies, rats fed miso developed fewer tumors when they were subjected to a cancer causing agent. And the rats fed miso were slower to develop tumors.
Researchers also investigated the incidence of tumors with miso and tamoxifen, a drug used for breast cancer treatment. The number of tumors per rat in the control group was 4.5. But in the group given miso, that number dropped to 2.4 and in the tamoxifen group it dropped to 1.4. When miso was given with tamoxifen, the number further decreased significantly to just 0.2 tumors per rat.
According to Watanabe, this investigation clearly indicates that miso can reduce the occurrence of breast tumors as effectively as tamoxifen at the beginning of cancer treatment, and can also suppress the number of tumors.
Miso Prevents Liver Tumors
When certain male mice were bred under normal conditions, 89% of them naturally developed liver cancer. But the mice fed diets containing 10% miso had their cancer rate drop to 32%.
In the same study, healthy mice were irradiated. Thirteen months later 62% of the male mice and 29% of females had liver cancer. But when mice were fed diets containing 10% miso, cancer rates decreased to 13% for both male and female mice.
In another study, when mice were injected with an agent causing liver cancer, the animals developed 46 tumors each. But mice fed miso developed only 32.5 tumors.
These laboratory studies confirm epidemiological findings that women without a history of liver disease who consume miso soup showed a significantly lower risk of developing liver cancer.
Miso Prevents Gastric Tumors
A large prospective study of 265,000 Japanese men and women found that eating miso soup on a daily basis might reduce the risk of stomach cancer. But since miso contains 10-12% salt, some researchers believe the sodium chloride (NaCl) in miso could actually increase the likelihood of stomach cancer.
To test the theory, researchers treated rats with a carcinogen for four months. The rats were simultaneously fed a diet supplemented with 10% dry red miso, 5% dry red miso, 2.2% NaCl (salt content equivalent 10% dry miso), 1.1% NaCl (equivalent to 5% miso) or a regular diet.
The rate of growth and size of gastric tumors in the groups fed miso were lower than in the groups fed added salt.
Even when a similar experiment was conducted with 50% salt-reduced miso, the incidence of gastric tumors was the same as with regular miso containing 2.2% NaCl.
Why would salty miso be more beneficial than plain salt? Some studies show that strains of yeast, lactic acid bacteria and other molds in miso can remove or detoxify carcinogens.
Others suggest a group of isoflavone-like substances in miso, such as biochanin A and genistein, prevent the growth of gastric tumor cells by stimulating death of cells by apoptosis.
Miso Protects Against Hypertension
Because of its high salt content, miso is often believed to increase blood pressure. But laboratory studies don't agree.
In one study, salt-sensitive rats were fed a regular diet (which contained 0.3% salt), or regular feed supplemented with 10% dry red miso (180-day fermented miso), regular feed supplemented with 2.3% salt (because 10% dry red miso contains 2.3% NaCl), or regular feed supplemented with 1.9% salt.
After 12 weeks, blood pressure in the rats fed miso or regular low-salt feed did not increase. Even though miso contains 2.3% NaCl, their blood pressure was as stable as in the rats fed a commercial diet containing 0.3% salt.
Although miso's antihypertensive action is not fully understood, these results indicate that salt in miso operates differently from NaCl at least in the case of gastric tumors and blood pressure.
How to Get Miso's Health Benefits
Miso is an essential ingredient in Asian cuisine. Prized for its versatility in cooking, miso can be used as bouillon, or a rich meat stock in soups and stews.
The color of miso can vary from light yellow to a deep dark brown. The lighter colors are more mild and good during warmer weather. Darker miso has earthy tones and a hearty flavor. It can be cooked with root vegetables, sea vegetables, and dark leafy greens during colder months.
When cooking with miso, use just enough to enhance flavor. Too much can overpower food with a strong salty taste.
Here are some great easy ways to enjoy miso in your meals:
- Dissolve a teaspoon of miso in hot water for a quick light soup broth
- Add miso to dipping sauces for spring rolls, norimake rolls or raw vegetables
- Mix light miso with vinegar, olive oil, ginger, and garlic for an Asian salad dressing on greens or grains
- Make miso-tahini sandwiches by spreading miso on a piece of bread and top it with tahini. Add sliced avocado or tomato as desired.
- Use miso as an ingredient in marinades for meat, fish, poultry or game.