Is miso soup safe during pregnancy?

What does the evidence say about miso soup during pregnancy?

1. Pregnant people are named as a high-risk group for listeriosis, and the specific foods flagged, unpasteurized dairy, raw or undercooked meat and fish, and refrigerated ready-to-eat spreads, don't typically include fermented, high-salt pastes like miso. 1
2. Miso's salt content, typically in the 11% to 13% range, combined with a pH that drops to around 5 during fermentation, creates conditions that inhibit unwanted microbial growth while allowing salt-tolerant fermentation microbes to thrive, giving traditional miso paste a different safety profile than a fresh or raw food. 2
3. In a large Japanese cohort study, miso soup intake of 1 to 2, 3 to 4, or 5 or more days a week before pregnancy was associated with lower odds of very early preterm birth (before 34 weeks) compared with less frequent intake, though the authors note the finding applies only to women at low risk for preterm birth and could reflect broader dietary or health patterns rather than miso soup alone. 3
4. Excess iodine intake during pregnancy, including from natural sources like seaweed, can disrupt thyroid function, and the WHO-recommended pregnancy iodine intake of 250 mcg a day sits well below the US upper limit of 1,100 mcg a day, so the seaweed-based dashi or wakame often used in miso soup is worth being mindful of if consumed very often. 4
5. Miso varieties differ widely in salt content, from around 6% in sweeter white miso to about 13% in red miso, so the sodium in a bowl of soup depends heavily on which variety and how much paste is used. 2

Is miso soup safe in each trimester?

• First trimester. A warm, salty broth like miso soup is often one of the easier foods to keep down during first-trimester nausea. Normal amounts are fine, and there's no pasteurization concern the way there is with raw dairy or undercooked meat.
• Second trimester. Nothing changes structurally in the second trimester. If miso soup becomes a near-daily habit rather than an occasional bowl, that's a reasonable point to start paying attention to how much seaweed-based dashi or wakame is in it, since that's the iodine source, not the miso paste itself.
• Third trimester. If you're managing blood pressure or swelling in the third trimester, miso's sodium content, which can run as high as around 13% salt by weight in some varieties, is worth factoring into your overall sodium intake for the day.