Fermented foods: sauerkraut, kimchi, kombucha and the evidence

Fermentation is microbes breaking down sugars and starches into acids, gases or alcohol. That covers a lot of the pantry: sauerkraut and kimchi, miso and tempeh, yogurt and kefir, sourdough, cheese, wine and kombuchaMarco 2017. They differ in one important way. Some still contain live microbes when you eat them (unpasteurized sauerkraut and kimchi, kefir, live yogurt, raw kombucha). Others are baked, canned or pasteurized, which kills the microbes, so shelf-stable sauerkraut in a can is a different food from the refrigerated kind.

A fermented food is not automatically a probiotic. "Probiotic" means specific live organisms shown to have a health effect at a stated dose; most fermented foods have not been tested that way Marco 2017.

Researchers randomized healthy adults to raise either fiber or fermented foods for 17 weeks, then measured gut microbes and immune markers in detail. The fermented-food group, eating foods such as yogurt, kefir, kombucha, kimchi and fermented vegetables, saw microbiome diversity rise steadily and inflammatory markers fall. The high-fiber group did not see a rise in diversity Wastyk 2021.

It is one trial with 18 people per group and no clinical outcomes, so the honest grade is limited. It is still a good reason to include a few live fermented foods if you like them.

Kombucha is sweetened tea fermented by a SCOBY, a rubbery mat of bacteria and yeast. Despite its reputation, a 2019 systematic review found just one human study and no clinical trials Kapp 2019. In 1995 the CDC and Iowa health officials investigated two cases of unexplained severe illness, one of them fatal, in people who had been drinking kombucha daily for about two months; the tea’s role was never established, but the episode is a reminder that home ferments are not risk-free CDC 1995.

If you want to brew it, follow a tested method. The National Center for Home Food Preservation publishes one that sanitizes equipment, checks the starter’s acidity, ferments for 7 to 10 days at 68 to 77°F, then refrigerates and uses the kombucha within 30 days. It also warns that sealed bottles build up carbon dioxide and can burst Nchfp.

For a live culture and proper glass or ceramic vessels, Kombucha Kamp sells SCOBYs and brewing kits. Home kombucha contains some alcohol, and the amount varies, so it is not for pregnancy, for children, or for anyone avoiding alcohol.

Aged and fermented foods, and some preserved meats, can contain tyramine, which can sharply raise blood pressure in people taking monoamine oxidase inhibitors (MAOIs). A 2018 review found modern food production has brought tyramine levels in most foods well down, and that most matured cheeses are now safe in normal portions, but it still advises care and individual judgment with high-risk foods such as some soy and fish sauces, salami-type sausages and some beers Gillman 2018. Follow the diet list from your prescriber.