When you think of the word “probiotics”, what comes to mind? A cup of yogurt or a bottle of dietary supplement capsules probably rises to the top, but over the last few years the presence of probiotics has expanded. Take a walk through the grocery store and you’ll see everything from fermented foods to fruit juices to baking mixes broadcasting their probiotic content. But does guzzling a kombucha have the same effect as taking a capsule? Are there benefits to probiotics for those of us who are already eat pretty healthy? And what the heck are Lactobacillus and Bifidobacterium?

Let’s back up for a minute and define the term “probiotic”. In 2001 the World Health Organization endorsed probiotics as, “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”. The premise is that consuming probiotics will enhance or restore balance to our gut microbiome which, if you’ve been keeping up with our Gut Check series, you know as the microbes that inhabit our gastrointestinal tracts. Probiotic bacteria are necessary for the fermentation of dairy products like yogurt and kefir as well as foods like kimchi and sauerkraut, and with their growing popularity it seems like probiotics are being added to all kinds of food and drinks. Probiotic-containing products will mention them on food packaging with the phrase “contains live and active cultures” and also listing specific types of bacteria in the ingredients list.

The problem is that at this point, we don’t know exactly what an “ideal” microbiome is, and it might vary from person to person. For a generally healthy person who isn’t struggling with gastrointestinal issues, it’s unclear if probiotics from food can truly take root in an already-crowded microbial landscape. Think about it: If millions and millions of gut bacteria have already staked a claim to all of the available real estate, it’s pretty tough for new ones to find their own patch of land. Consequently, it’s thought that many probiotic strains are transient citizens of the gastrointestinal tract, making an appearance after we eat, drink or swallow them and then going on their way. In this sense, maintaining a continual presence of these probiotic microbes would require repeatedly re-introducing them – for example, by taking several probiotic capsules per day or making yogurt part of your daily eating pattern.

That’s not to say that these transient strains have no impact at all. While in the gut they may interact with other “resident” strains, involve themselves in metabolism or influence the pH balance of their environment, which can affect the type and activity of bacteria that reside there. But these effects are variable and can change over time.

To complicate things even further, there are many different strains of probiotics, and research studies often evaluation just one of them or a mix of a few. This means that the results of one study can’t be applied to the probiotics category as a whole. It’s also problematic that most probiotic studies are small and use different doses and delivery methods (capsule versus food, for example). And lastly, it’s unclear if some products that promote their probiotic content actually deliver on that claim. Many strains of bacteria are killed off by high temperatures, meaning that your probiotic muffin mix might just make tasty – but microbe-free – baked goods. In short, we’re a long ways off from making sense of how – or if – probiotics impact the health of most people.

But there are a few very important exceptions. The most compelling evidence of benefits from probiotics is found in studies of patients suffering from conditions associated with severe gastrointestinal conditions. Introducing certain strains of probiotic bacteria (commonly including Lactobacillus and Bifidobacteria) into the gastrointestinal tract has been shown to reduce antibiotic-associated diarrhea, prevent a serious gastrointestinal condition that can affect premature infants, decrease symptoms in some patients with irritable bowel syndrome and reduce the risk of C. difficile-associated diarrhea. A 2018 summary of Cochrane systematic reviews concluded that probiotics “can have a beneficial effect on diarrheal conditions and related GI symptoms”.

Let’s close with responses to two important questions: what remains to be done, and what should you do? First, more research is needed to determine which strains of bacteria are most likely to show benefit, which delivery method is optimal and what amounts are ideal.  As such, it’s very possible that some benefits of probiotic foods and drinks have yet to be discovered.

Until we know more, there are a few important points to consider. Remember that at this point, it’s unclear if there are any benefits to consuming probiotics if you’re a generally healthy person. That said, there’s probably no physical harm in doing so. Probiotics are considered to be dietary supplements and therefore are not regulated by the Food & Drug Administration, though studies show that they’re generally safe for healthy individuals. Regardless of probiotic content, foods like yogurt, tempeh, miso, kimchi and sauerkraut are rich in many other nutrients that our bodies need for optimal health, including protein, calcium and B vitamins. Lastly, if you’re struggling with a gastrointestinal condition or have recently finished a round of antibiotics, popping a probiotic or drinking some kefir may be a good thing – as long as your healthcare provider approves.