If I Eat Fermented Foods, Do I Need a Probiotic?

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. Foods like kefir, kombucha, and kraut 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 benefits. This begs the question: If you eat fermented foods, do you even need to take a probiotic for gut health?

Here, we’ll break down the definition of probiotics and fermented foods, and explain why they aren’t interchangeable.

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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 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 oftentimes extremely nutritious options to include in your diet. So it’s not an “either/or” situation. 

The long answer: Since the process of fermentation requires microbes, fermented foods and beverages are often conflated with probiotics. But just because a product contains microbes doesn’t mean it meets the scientific definition of a probiotic.

According to 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, strengthening the gut barrier 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.” 

EXPLORE FURTHER: Probiotics 101

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.

A variety of reactions and pathways can be involved in food fermentation. Variables like temperature, pH, water activity, and time can all contribute to the final outcome.² But ultimately, 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. 

Why Fermented Foods Can’t Replace Probiotics

Fermented foods and beverages rarely, if ever, meet the criteria for a probiotic.³ They are not created using controlled studies that show which exact microbes are present, in what quantities, and to what effect. 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? 

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.

If you want to get verifiable probiotic benefits, you’ll most likely need to get them through supplementation. (Though, even within probiotics, there is a lot of variability. 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. Fermented foods can absolutely be a nutritious addition to any gut-healthy diet. Probiotics can too.

The Key Insight

Fermented foods and probiotics are not the same thing. Drinking kombucha and eating kraut doesn’t necessarily benefit your gut health in the same way that taking a science-backed probiotic does.

At the end of the day, the more (beneficial bacteria) the merrier. 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 gut microbiome.