Why does miso soup give my diarrhea? Koji might be the cause

by Joost Nusselder | Updated:  May 26, 2022

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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, which is a probiotic that’s full of fiber to get things moving for you. 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 that’s in yogurt to help you poop is in miso soup.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 go on and 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 probiotics 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

Ever had trouble finding Japanese recipes that were easy to make?

We now have "cooking Japanese with ease", our full recipe book and video course with step-by-step tutorials on your favorite recipes.

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.