Why do I get diarrhea from miso soup? Koji might be the cause!

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If you’ve had a delicious bowl of miso soup, then later, weren’t able to get off of the toilet because of diarrhea, there’s a reason for that.

You might get diarrhea because miso soup has koji, a probiotic full of fiber. It also has soybeans and sea salt that’ll aid in loosening up your bowels. Another reason is that miso soup is fermented. The same live, cultured bacteria in yogurt to help you poop.

Let’s look at how miso soup affects your stomach and bowel movements.

Why does miso soup give me Diarrhea

Also read: use these ingredients as the perfect miso paste substitutes

So if you don’t have a good ratio of bad-to-good gut bacteria, then drink miso soup, you could really upset your stomach’s pH balance and cause everything to happen very quickly in there.

What exactly is miso? Find a detailed answer from YouTube user Erica Yi Yeah:

The probiotics in koji and the fiber in the soybeans can cause diarrhea if your body isn’t used to having probiotic food regularly. That’s why it’s so important to have a balanced diet!

Once you know how you react to miso soup, or once you’ve adjusted your diet to regularly have more fiber and probiotics, then you won’t have that problem anymore.

Just like any change in your diet, the first time eating a kind of new food can really mess up your stomach.

Also read: don’t want miso soup? Try Japanese clear broth instead

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Gut-calming miso soup recipe

Here’s a quick recipe for a gut-calming miso soup that you can make at any time in the comfort of your home.

bowl of saikyo miso soup with green onions and tofu with bowl of green onions and chili peppers next to it

Gut-calming miso soup

Joost Nusselder
This healthy vegetable soup is vegan, gluten-free, grain-free, gut-healthy, and very simple to make. It's also loaded with many vitamins that improve gut health.
No ratings yet
Prep Time 10 days
Cook Time 30 days


  • Kombu
  • 6 cups Water
  • Umami powder
  • Dried shiitake mushrooms
  • Taro root
  • Carrot
  • Onion
  • Button mushrooms
  • Napa (Chinese) cabbage
  • 1-2 tbsp Yellow miso paste
  • Sliced green onion (optional)


  • Chop all the vegetables up. You can use as little or as much as you want in this soup.
  • Fill a big soup pot with kombu, dried shiitake mushrooms, water, umami spice, or a dashi packet.
  • After the water boils, remove and discard the kombu, reduce the heat, and then add the remaining ingredients, excluding the miso paste. Cook vegetables for 25 minutes or until soft.
  • Scoop 1-2 tbsp of miso paste into a ladle and turn off the heat. When the miso is thoroughly combined with the broth, add more liquid and gently stir the paste into the hot broth in the ladle. Mix well after adding it to the soup.
  • Pour into dishes and garnish with green onion slices.
  • Serve and enjoy relaxing your tummy!
Tried this recipe?Let us know how it was!

Miso soup is considered a comforting food that helps with the digestive system. So whenever you’re craving Japanese soup, just grab yourself a gut-calming vegetable miso soup and boost your healthy gut flora.

Miso soup health benefits

Many Japanese eat miso soup, and it’s not just because it’s delicious!

Miso soup also offers many health benefits. At a glance, it’s already loaded with protein, calcium, manganese, zinc, potassium, and vitamin K.

Having a bowl of miso soup regularly is also found to reduce the risk of stomach and breast cancer, improve heart health, boost the immune system, and promote brain health.

Diseases like high blood pressure, and other health problems like digestive issues or stomach problems, and even acid reflux are known to be reduced by having a bowl of miso soup.

The primary probiotic bacteria identified in miso is Aspergillus oryzae, which is also present in fermented soybean paste miso soup. According to studies, this condiment’s probiotics may help lessen symptoms of digestive disorders like inflammatory bowel disease (IBD).

Due to its high antioxidant levels of vitamin E, amino acids, saponin, and lipofuscin, miso possesses anti-aging properties. The body is also strongly alkalized by miso, which strengthens the immune system.

Miso is generally healthy for most people to eat, but because of its high sodium content, you may want to limit your intake if you follow a low-salt (sodium) diet. This is a result of soybean oil’s goitrogenic properties. You might need to cut back on your intake if you have a thyroid issue.

Where to shop for miso

If you fancy having a bowl of miso soup as soon as possible to save yourself from the hassle of cooking, you can buy it downtown or order it online.

You can typically find miso in most Asian stores, but if you want to order online, here are some of my top favorites:


Let’s clear up some things by answering some of your questions.

Can you get food poisoning from miso soup?

Miso soup carries a risk of food poisoning due to the use of unpasteurized miso paste in many recipes. If the soup isn’t made properly, it may also serve as a breeding ground for bacteria.

Miso soup can cause food poisoning, which can present as nausea, vomiting, and diarrhea. It’s crucial to visit a doctor right away if you start to feel this way after eating miso soup.

What does miso soup taste like?

Miso soup has a flavor that’s rich, salty, and tangy, but not overbearing.

If you’re just starting off, then you might want to experiment with softer and lighter miso. White miso soup is sweeter than red miso soup, but it still tastes great.

Is it okay to have a bowl of miso soup every day?

Although miso has a high sodium content and is typically safe for most individuals, those who follow a low-sodium diet may want to limit their intake.

Beans are thought to cause goiters. So you should reduce your miso soup intake if you have a thyroid condition.

How can you store miso soup?

Miso soup can be kept in the refrigerator for 2 to 3 days in an airtight container. For optimal results, separate any tofu, seaweed, or green onions from the miso soup before keeping.

Miso soup can be kept at room temperature for up to 2 hours before it needs to be stored.

Is miso high in calories?

Because it includes so little fat and carbohydrate, miso soup typically is considered low-calorie. If you make miso soup with only miso paste and Japanese stock, your serving size is likely to be around 50 calories.

Take it easy with miso soup

Miso soup is a sweet combo of nutrient-packed and deliciousnous, and it’s well-loved by the Japanese, as well as by people who want to get a taste of Japanese cuisine.

However, despite that, consuming miso soup should be done in moderation if you have to take a diet low in sodium, as miso soup contains a lot of salt.

If it’s your first time having miso soup, it’s best to take it slow, as you’ll possibly get diarrhea if you overdo it. It’s also best to pair it with other dishes like fresh sashimi salad, fried tofu, steamed veggies, or even steak.

Do you want to give yourself a nutritious bowl of soup? Try miso today!

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Bitemybun's family recipes with complete meal planner and recipe guide.

Try it out for free with Kindle Unlimited:

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Joost Nusselder, the founder of Bite My Bun is a content marketer, dad and loves trying out new food with Japanese food at the heart of his passion, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with recipes and cooking tips.