Why Does Miso Soup Give Me Diarrhea? “Koji” might be the cause

by Joost Nusselder | Updated:  November 15, 2020

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If you have had a delicious bowl of miso soup and then later not been able to get off of the toilet with diarrhea, there’s a reason for that.

You might get diarrhea because miso soup has koji which is a probiotic that is full of fiber to get things moving for you. It also has soybeans and sea salt that will aid in loosening up your bowels. Another reason is that miso soup is fermented. The same live, cultured bacteria that is in the 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, and then go on and eat miso soup, you could really upset your stomach’s pH balance and cause everything to happen very quickly in there.

The probiotics in the 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

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.