Fermented Foods: the Fad and the Facts

Fermented foods are the rage. The fervor for these foods is driven in part by the expanding knowledge about microbes being our unseen partners. There was a time when the term ‘microbe’ called to mind only those few that legitimately threaten to harm or even kill. But sensibilities today lean more to recognizing that most microbes aren’t to be feared, and in fact, play an important role in developing and maintaining our health.

Social media explodes with information on fermented foods, each article seeming to try to outdo the next with how many fermented foods you can’t afford to live without:

Regardless of the number of “must-have” fermented foods the internet insists you must have, there are a few key points worth noting about the science behind fermented foods.

First, not all fermented foods are created equal. They are all produced through the action of live microbes, but many fermented foods are subsequently processed in a way that kills or removes the fermenting microbes before they are consumed. Sour dough bread, wine, many beers, and many unrefrigerated fermented foods such as canned olives, sauerkraut and the like are fermented but do not contain live microbes. Others are pasteurized after fermentation and then a single strain ‘probiotic’ added back.

Second, not all fermented foods are probiotic foods. Probiotics must be alive when consumed and must have been studied and shown to confer a health benefit. Many fermented foods fall short of these requirements. See the difference between fermented foods and probiotics.

Third, there may be limitations to the evidence for health benefits of many popular fermented foods such as kombucha, kefir, tempeh, sauerkraut, and kimchi. Much of what we know comes from studies that associate health benefits with consumption of certain types of fermented foods, but such studies don’t prove that the fermented foods cause the benefit. It might be that people who consume fermented foods engage in other behaviors that are the real cause of benefit. An important exception to this caution has to do with the body of evidence surrounding probiotic yogurts. Often, in addition to the fermentation bacteria that transform milk into yogurt, yogurts contain extra added probiotic bacteria that have been tested in controlled human trials for their health-promoting ability.

Lastly, fermented foods are not essential for your health. Certainly, top microbiome experts speak to the value of fermented foods in your diet. But much of this is hypothesis-driven and lacks direct evidence. Such opinion is balanced by the fact that these foods are often nutritious and surely safe – so there is no downside to including them in a healthy diet. Dietary fibers, which can serve as food sources for the microbes already living in you, are also a favorite practical recommendation of microbiome experts.

So enjoy your fermented foods, but appreciate the limitations to the science and the communications about them.


For fact-based information on fermented foods, the International Scientific Association for Probiotics and Prebiotics (ISAPP) has developed some consumer friendly materials: see this ISAPPscience.org webpage. (Full disclosure: I serve as the executive science officer of ISAPP.)