Reader’s Digest: If I Eat Fermented Foods, Do I Need a Probiotic?
There’s a difference between fermented foods and probiotics (even if labels tell you otherwise). Here’s why both are great additions to your routine.
Reader’s Digest is where we answer common questions about digestive health as simply and jargon-free as possible. If you’re seeking snackable info, start with our short answer. Hungry for more? Dig into our longer explanation. Have a question of your own that you’d like us to break down in a future Reader’s Digest? DM us on Instagram.
Fermentation is having a moment. Products like kefir, kombucha, kimchi, sauerkraut, miso, raw cheese, pickles, and sourdough bread are popular all over the world not just for their unique taste (is it sour, tart, earthy, funky?), but also because they can offer a range of potential health benefits. Since the process of fermentation requires microbes, fermented foods and beverages are often conflated with probiotics—as well as the beneficial effects that a validated probiotic can offer. But just because a product contains microbes, doesn’t mean it meets the scientific definition of a probiotic. (We’ll get to that in a bit.)
Here, we’ll break down the differences between the two, and explain the answer to one of our most commonly asked questions.
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If I eat fermented foods, do I need a probiotic?
The short answer: Contrary to what many think (and what labels may incorrectly tell you), fermented foods and probiotics are not necessarily one and the same. If you want specific, scientifically validated health benefits, your best option is to take a probiotic supplement. But fermented foods can be delicious and nutritious options to include in your diet. So it’s not an “either/or” situation.
The long answer: Let’s start with the scientific definitions, since these two terms have relatively precise ones codified by the International Scientific Association for Probiotics and Prebiotics (ISAPP). Probiotics are defined as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.”1 (Fun fact from the Seed-verse: This definition was first authored by a 2002 UN/WHO expert panel, chaired by Seed’s Scientific Board Member Dr. Gregor Reid.)
What does this definition really mean? Let’s break down a few critical components:
- Live microorganisms: Probiotic organisms need to be alive at the time of consumption. This means they have to survive processing, shipping, and the time they sit in their packaging before they’re taken by you. It also needs to be clear what kind of microbes are in the probiotic, ideally at the strain (versus species) level.
- Adequate amounts: The microbes in a probiotic must be alive, but also in high enough quantities to have an effect when they’re taken. The number of the microbes in a probiotic dose will be listed on the label, measured in either CFU (colony forming units) or, our preferred method, AFU (active fluorescent units). This amount should match the dosage that was used in the corresponding research to demonstrate the benefit of the particular bacterial strain (more on that, next).
- Confer a health benefit on the host: There needs to be a measurable health benefit, proven by research—for example, producing a vitamin or increasing the frequency of bowel movements. This is done by evaluating the effect of a specific strain of bacteria on the host (the person taking the probiotic), using an appropriately sized and designed study. Only once a bacterium has demonstrated a concrete health benefit in a given host, may it then be designated a “probiotic.”
On the other hand, ISAPP defines fermented foods as “foods made through desired microbial growth and enzymatic conversions of food components.”2 Translation: A fermented food or beverage is one in which microbes have been intentionally used to change certain properties of that food or beverage.
To better understand this definition, let’s unpack what fermentation really means. Fermentation is a chemical process in which microbes break down large compounds or molecules into smaller ones. There are a variety of reactions and pathways that can be involved in food fermentation, and variables like temperature, pH, water activity, and time can all contribute to the final outcome.2 But microbes are directing the show, determining the course of the fermentation process, and the final smell, taste, appearance, preservation, and nutritional properties.2 For example, kombucha is made when certain bacteria and yeast are added to sweetened tea. The bacteria and yeast will feed on the sugar in the tea and produce a variety of substances in the process, like acids, alcohol, and gasses that transform the raw ingredients into this popular fermented beverage.
Fermented foods and beverages rarely, if ever, meet the criteria for a probiotic.3 For one, there are no controlled studies that show which exact microbes are present, in what quantities, and if they actually confer a measurable health benefit. Meaning: Their benefits are really hard to prove. If you drink kombucha or consume kimchi, you might have ingested some bacteria, but are they still alive at the time of consumption? Which strains are included? In what quantities? Have these specific bacteria been studied to deliver a measurable health benefit in humans?
So, from a scientific standpoint, fermented foods and beverages should not be labeled as probiotics themselves, but rather represented as containing “live and active cultures.”2 But like we said, that doesn’t necessarily stop companies from falsely labeling their fermented products as “probiotics” (and inflating their purported benefits in the process), so it’s important to understand what you’re buying and putting in your body.
Moral of the story: Unlike probiotic supplements or therapeutics, fermented foods have a much less specific scientific threshold to meet their definition. While they may offer similar benefits to probiotics, in most cases, there’s no way to know for sure. So, if you want to get verifiable probiotic benefits, you’ll most likely need to get them through supplementation (though even with probiotics, there is a lot of variability, and not all products are created equal).
The good news? It’s not a binary choice (why not both?). When it comes to the gut microbiome, diversity is critical—it’s one of the primary markers of gastrointestinal health. So consuming both fermented foods and a scientifically validated probiotic as a part of your daily routine may provide exposure to a variety of bacterial strains, which could help promote the diversity and richness of the microbiome. At the end of the day, the more (beneficial bacteria) the merrier.
- Hill, C., Guarner, F., Reid, G., Gibson, G. R., Merenstein, D., Pot, B., Morelli, L., Canani, R. B., Flint, H. J., Salminen, S., Calder, P. C., & Sanders, M. E. (2014). The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology, 11(8), 506–514. https://doi.org/10.1038/nrgastro.2014.66
- Marco, M. L., Sanders, M. E., Gänzle, M. G., Arrieta, M. C., Cotter, P. D., De Vuyst, L., Hill, C., Holzapfel, W. H., Lebeer, S., Merenstein, D., Reid, G., Wolfe, B. E., & Hutkins, R. W. (2021). The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nature Reviews Gastroenterology & Hepatology, 18(3), 196–208. https://doi.org/10.1038/s41575-020-00390-5
- Vinderola, G., Cotter, P. D., Freitas, M., Gueimonde, M., Holscher, H. D., Ruas-Madiedo, P., Salminen, S., Swanson, K. S., Sanders, M. E., & Cifelli, C. J. (2023). Fermented foods: a perspective on their role in delivering biotics. Frontiers in microbiology, 14, 1196239. https://doi.org/10.3389/fmicb.2023.1196239