Medically reviewed by Kayla Girgen, RDMedically reviewed by Kayla Girgen, RD
Miso is a fermented food made from soybeans and grains. It's used as a seasoning in Japanese cuisine. There are multiple types of miso. These types are classified according to the grains used in the process, such as rice, barley, and mixed miso.
It contains soybean proteins, sodium, small amounts of vitamins and minerals, and non-nutritive compounds that have certain health-promoting properties. As a fermented food, miso contains probiotics that promote gut health. It's also rich in antioxidants, which can reduce damage and promote healthy cells.
Fermented soybean foods, including miso, contain antioxidant compounds. Antioxidants help prevent cell damage and disease by neutralizing free radicals, naturally occurring compounds that are a by-product of metabolism. Free radicals also occur as a response to external factors such as pollution, ultraviolet light, and smoking.
Oxidative stress -- a bodily state that can cause cell damage and contribute to disease -- occurs when free radical levels become too high. Eating foods high in antioxidants, like miso, helps keep free radicals in check, reducing disease risk.
Fermented foods are made using microorganisms such as bacteria and yeast. These microorganisms metabolize foods -- typically dairy, soybean, or tea -- into fermented products such as kefir, miso, and kombucha. The final fermented product has a distinct taste and contains beneficial bacteria that can improve the health of your gut.
Miso contains probiotics such as Bacillus species, which are beneficial bacteria for humans. Probiotics can improve gut health by inhibiting pathogens (disease-causing bacteria), producing antimicrobial compounds, supporting the gut barrier, and improving nutrient absorption.
Probiotics may also improve a wide range of health conditions, including bowel diseases, antibiotic-associated diarrhea, constipation, allergy-related conditions such as atopic dermatitis, and conditions affecting the skin and respiratory system.
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Consuming miso may benefit heart health. Although miso is high in sodium, it's also high in fiber and health-promoting compounds, both of which can support heart health.
A randomized-controlled study looked at how miso soup affects nighttime blood pressure. People with slightly high or stage 1 high blood pressure were given either miso soup (containing 3.8 grams of salt) or other soy foods with much less salt (0.2 g of salt).
Both types of food had similar nutrients, but miso had more fiber and sodium. After eight weeks, people who consumed miso soup had lower nighttime blood pressure. Their daytime blood pressure didn't change compared to the people who ate other soy foods.
Strong evidence does show that high sodium intake increases the risk of heart disease. While miso soup may lower blood pressure, the effects are limited and need more research.
Whether soy products prevent or contribute to cancer has long been debated. A research review showed no relation between the consumption of soy products and death due to cancer. This conclusion is based on seven cohort studies with follow-ups ranging from 7-18 years, tracking the long-term health changes of participants in relation to their consumption of soy products.
Another recent review concluded that high consumption of soy products is linked to a reduced cancer risk. However, no significant association was found between cancer risk and the individual effects of consuming miso soup, fermented soy products, nonfermented soy products, and soy paste.
Other research has shown that soy products are associated with gastric cancer. While some evidence indicates that consuming soy products can reduce the risk of gastric cancer, other evidence suggests that high-sodium foods can contribute to the risk. For example, people who consumed three to four bowls of miso soup a day had a 60% higher risk of gastric cancer than those who did not.
The effects of soy products, including miso, on cancer are unclear.
Miso contains many nutrients but is typically consumed in smaller amounts. One tablespoon (tbsp) of miso provides:
Although smaller quantities of miso do not provide substantial vitamins and minerals (except sodium), miso contains many non-nutrient compounds called isoflavones, which are associated with various health benefits.
Miso contains high amounts of sodium. Just one tablespoon of miso contains 634 mg of sodium, which is more than one-fourth of the recommended daily sodium limit of 2,300 mg. Limiting sodium intake is especially important for people with heart disease or at a high risk of developing heart disease.
High sodium intake is associated with an increased risk of high blood pressure, heart disease, gastric cancer, osteoporosis, and kidney disease. However, you can find reduced-salt miso, which contains 25-50% less sodium than regular miso. If you really enjoy miso, you can still eat it by adjusting other sources of sodium in your diet.
Major food allergens include milk, eggs, seafood, peanuts, wheat, and soybeans. Miso is made from soybeans, rice, or barley. If you have a gluten (found in wheat and wheat products) or soy allergy, you should be cautious with miso, as it can cause serious allergic reactions.
You can find gluten-free miso if your only allergy or intolerance is to gluten.
Fermented products contain living organisms called probiotics. Although it's rare, uncontrolled environmental conditions during the fermentation process can sometimes allow harmful bacteria to grow in miso -- leading to microbial outbreaks.
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Whether you're a lover of miso or have never tried it before, these tips can elevate your culinary experience:
Miso is a fermented food that contains probiotics and antioxidant compounds. Eating miso may support gut and heart health, protect cells from damage, and reduce cancer risk. However, evidence for these benefits is limited.
You can enjoy miso in moderation while monitoring your sodium intake. You should avoid miso if you have a soy or wheat allergy or gluten sensitivity.