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Are fermented foods “probiotic”? (December 2024)

—Carrie Dennett, MPH, RDN

Do you make your own yogurt or have a sourdough starter you’ve been nurturing for years? Maybe you frequently add kombucha and kimchi to your shopping list? If so, you’re in good company. These and other fermented foods have a long and illustrious history—fermentation was a biological method of food preservation long before we had refrigeration or preservatives—yet are appealing to modern sensibilities. That’s in part due to interest in supporting a healthy gut microbiota (the community of microorganisms that live in our large intestine), but also because of how fermentation can elevate humble foods.

Fermentation is the slow, controlled decomposition of organic substances by microorganisms (usually bacteria or yeast) or enzymes. This process may occur naturally and spontaneously, as when you make sauerkraut or sourdough bread at home, or through careful addition of a starter culture, which you would do if you were making yogurt or kombucha.

One common myth about fermented foods is that they are the same thing as “probiotics,” live microorganisms which, when administered in adequate amounts, offer a health benefit. Certainly, some fermented foods contain live microorganisms. These include fresh kimchi, sauerkraut and sour dill pickles as well as yogurt, kefir (a fermented dairy beverage), kombucha (fermented tea), miso, some cheeses, traditional salami and European-style dry fermented sausage, and microbrewed beer that hasn’t been filtered or heated.

These microorganisms could offer health benefits—some research has observed subtle-but-positive changes in the gut microbiota of people who regularly eat fermented foods—but is it because they’re probiotic? Maybe yes, maybe no.

While many fermented foods offer “adequate amounts” of live microorganisms, they don’t all contain microbial species that have been defined, characterized, and tested to determine if they offer specific health benefits. In many cases, this is logistical, because specific microorganisms can vary by batch, producer and location. For example, a sourdough starter in San Francisco doesn’t contain the exact same microorganisms as one in Seattle. Yogurt is one of the few examples of a fermented food that is also probiotic, because the primary bacteria species used in fermentation are plentiful, consistently used and well understood.

One real tangible benefit of fermented foods is making foods such as cabbage, wheat and dairy more digestible for some people who find it challenging to eat them in their simpler forms. For example, the bacteria that turn milk into yogurt digest much of the lactose—the natural sugar in milk and dairy—making the yogurt more digestible for many people who are lactose intolerant.

This benefit can persist even when the live microorganisms responsible for fermentation are destroyed or removed post-fermentation by baking, pasteurization, canning or filtering. This happens with sourdough bread, tempeh, most soy sauces, most beer and wine, chocolate, and self-stable sauerkraut, pickles and kimchi. Also, many fresh cheeses are heated, and most of the live bacteria used to create aged cheese are used up during the aging process.

Fermented foods are delicious, and there’s little downside to consuming them as part of a balanced, nutritious diet. Enjoy kombucha as a low-to-no alcohol cocktail—“non-alcoholic” kombucha has less than 0.5 percent alcohol by volume (ABV). Try sauerkraut instead of pickles in tuna salad, on sandwiches, and in place of cabbage on fish tacos. Add sauerkraut or kimchi to grain bowls or on top of scrambled eggs. Use yogurt or kefir in your smoothie or cereal bowl. But if you specifically need to take probiotics, look to the dietary supplement aisle.

References:

  • Fermented Foods. International Scientific Association for Probiotics and Prebiotics. https://isappscience.org/fermented-foods/
  • Hutkins R. Your guide to the difference between fermented foods and probiotics. Gut Microbiota News Watch. http://www.gutmicrobiotaforhealth.com/en/guide-difference-fermented-foods-probiotics/
  • Fernández M, Hudson JA, Korpela R, de los Reyes-Gavilán CG. Impact on human health of microorganisms present in fermented dairy products: an overview. Biomed Res Int. 2015;2015:412714.
  • Kim B, Hong VM, Yang J, et al. A Review of Fermented Foods with Beneficial Effects on Brain and Cognitive Function. Prev Nutr Food Sci. 2016 Dec;21(4):297-309.
  • Marco ML, Heeney D, Binda S, et al. Health benefits of fermented foods: microbiota and beyond. Curr Opin Biotechnol. 2017;44:94-102.

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