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Fermented vegetables and soy

Also: kimchi · sauerkraut · miso · tempeh

A small but well-run trial found a fermented-food diet increased gut microbe diversity. Early days.

Overall evidence

Evidence level: Limited or early evidence

One small, careful trial plus a lot of interest; not yet enough to say what it means for health.

A few small or low-quality studies, inconsistent results, or mostly lab and animal work. Interesting, but not enough to rely on.

Sauerkraut
Photo: Eugene Zelenko, via Wikimedia Commons (CC-BY-SA-4.0)

What it is

Vegetables, soybeans and grains transformed by bacteria, yeasts or moulds: kimchi and sauerkraut (lactic-fermented cabbage), miso (fermented soybean paste) and tempeh (fermented soybean cake).

Traditional use

Tradition, not evidence: how cultures use it, not proof that it works.

  • Korea

    Kimchi is served at nearly every meal, and kimjang, the communal autumn kimchi-making, is a cultural tradition.

  • Central and Eastern Europe

    Sauerkraut was a winter vegetable store; its brine is drunk as a folk tonic.

  • Japan and Indonesia

    Miso soup is a daily staple in Japan; tempeh is an everyday protein in Java.

What the research says

Each claim graded on its own evidence.

  • Fermented foods and the gut microbiome

    Evidence level: Limited or early evidence

    In a 2021 randomised study of 36 healthy adults, a 10-week diet high in fermented foods increased gut microbiota diversity and lowered several inflammatory markers. It was small and short, and did not measure health outcomes.[1]

In food amounts

A few forkfuls of kimchi or sauerkraut as a side, a bowl of miso soup, or tempeh as the protein in a meal.

We describe everyday cooking amounts only, never supplement doses.

Safety

Medicines
Fermented soy foods such as miso, tofu and soy sauce are high in tyramine, which has been linked with dangerous rises in blood pressure in people taking MAOI antidepressants.[3]
Allergies
Miso and tempeh are made from soybeans, a common allergen; some kimchi contains fish or shellfish.[3][4]
Health conditions
Kimchi, sauerkraut and miso can be very salty. The WHO recommends adults keep salt below 5 g a day.[2]

If you take regular medicines, are pregnant or breastfeeding, or are cooking for a baby or someone who is unwell, check with a doctor, pharmacist or midwife before using any food or supplement for a health reason.

Sources

  1. [1] Gut-microbiota-targeted diets modulate human immune status (Wastyk et al.) — Cell 184:4137–4153, 2021
  2. [2] Healthy diet — fact sheet — World Health Organization
  3. [3] Soy — fact sheet — US National Center for Complementary and Integrative Health (NCCIH, NIH)
  4. [4] Food allergy — NHS (UK)

Sources were checked when this entry was written. Research changes; if you spot something out of date, please tell us.

Cook with fermented vegetables and soy

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