Probiotic supplements aren’t just trendy, they’re ubiquitous. You can find bottles of probiotic pills, powders, and liquids for sale at any supermarket, each promoted as a cure for various ills: digestive issues, fatigue, weak immunity, brain fog, and more. While the evidence on these benefits is lacking, the marketing messages are working; the global probiotic market was worth about $49.4 billion in 2018, and forecasting experts estimate it will grow to $69.3 billion by 2023. Prebiotics, the fibers that feed probiotics, have been riding the coattails of this popularity for some time. Now postbiotics—the metabolites produced when probiotics eat prebiotics—have hit the scene. They’re being sold as supplements and are starting to make the rounds on nutrition-focused corners of the internet.
The hype around all of these microbes makes sense. Yes, prebiotics, probiotics, and postbiotics can enhance health by positively influencing the microbiome, a term that refers to the multitudes of microorganisms that live within you, explains Carolina Guizar, a New York–based dietitian and owner of the nutrition-coaching platform Eathority. But as with probiotics and prebiotics, the postbiotic market is several steps ahead of the actual science.
While the microbiome has been a hot topic among nutrition experts (and amateur enthusiasts) for about a decade, microbiome research is still in the very early stages. A 2018 review of the literature published in the European Journal of Nutrition starts its conclusion with: “The role of the human gut microbiota in health and disease is beginning to be understood.” The authors tell us what we know, which is that the gut microbiome plays a role in mood regulation, cognition, immune function, and digestive health. But they also explain that the details are still unclear: we aren’t exactly sure what the benefits are, how the various microbes deliver them, and whether or not supplements offer any measurable benefits. Here’s what experts have to say about the state of the evidence.
It’s All Connected
We can’t talk about postbiotics without first talking about prebiotics and probiotics, because none of them stand alone. Probiotics are beneficial bacteria that live naturally in your microbiome. Your microbiome exists all over your body, but here we’re talking primarily about your gut.
Probiotics are powerful. A 2019 review in Future Science OA found significant evidence for the digestive benefits of probiotics and promising evidence for their potential impact on mood and mental health. But it’s not as simple as just taking one supplement and expecting something to happen, explains George Weinstock, a University of Connecticut professor and the director of microbial genomics at the Jackson Laboratory, a global nonprofit biomedical research institute. “Probiotics” is an umbrella term for a variety of different bacteria. Roughly 5,000 strains from 1,000 species have been found in the human gut microbiome, although not everyone has all of them. Each strain acts slightly differently and has different potential health benefits.
Probiotics can’t do their thing without the help of prebiotics, a type of fermentable fiber found in plant foods that feed probiotics and keep them alive. Tamara Duker Freuman, a New York–based dietitian and author of The Bloated Belly Whisperer, explains that when probiotics feed on prebiotics, they produce postbiotics, health-promoting by-products called microbial short-chain fatty acids. As with probiotics, “postbiotics” is an umbrella term that encompasses several different chemical compounds, all with different characteristics and potential health benefits.
Skip the Supplements
“Microbiome research really only hit the headlines a little over ten years ago,” Weinstock says. Since then the market has exploded with supplements meant to improve the microbiome, and the public is increasingly interested in how food might affect it as well.
We know that a diet high in plant-based foods is key for the body’s production of prebiotics. “The main sources of prebiotics in the typical American diet are whole-wheat bread, onions, and garlic—but so many other foods contain them,” Freuman says. Many fruits and vegetables contain prebiotics, including apples, pears, mushrooms, artichokes, cauliflower, and jicama. Beans, lentils, barley, and rye also have significant amounts of prebiotic fiber. We need to consume prebiotic fibers regularly to reap their benefits—our bodies don’t naturally house them and can’t produce them. Since they’re so prevalent in common foods, supplements aren’t really necessary.
Probiotics are also present in our foods, primarily in fermented ones like yogurt, kimchi, sauerkraut, and cheese, and in supplements. But what many people don’t realize is that, generally speaking, probiotics from your diet don’t have a huge impact on your gut microbiome. There are somewhere around 100 trillion bacteria in your gut. “When you take a probiotic supplement or eat a food that contains probiotics, you’re introducing them to a habitat [your gut] that’s already densely populated with microorganisms,” Weinstock explains. A supplement may boast “one billion live probiotics,” but that’s just 0.001 percent of the bacteria already in your gut. Those one billion probiotics have to fight hard to colonize your already-packed microbiome and might end up just passing through your stool.
Weinstock also notes that although labels make it seem like probiotic supplements contain a huge variety and number of beneficial bacteria, this isn’t the case. Practically all probiotic supplements contain bacteria from just two genera: Lactobacillus and Bifidobacterium. The Food and Drug Administration deems them safe because they’re found in common foods that we’ve been eating for centuries, like cheese. So you’re not really getting any additional benefit from these supplements, because they only contain probiotic strains that are already in your diet.
Countless other potentially beneficial strains and species are being examined. This 2020 review in the International Journal of Microbiology summarizes recent studies looking into various probiotics for potential benefits ranging from diabetes prevention to HIV treatment. Remember, up to 5,000 strains have already been found in the human gut microbiome—but their effect on the body is not yet understood, so they’re not yet approved for sale or consumption. Even when other strains start being approved, you’ll only benefit from supplementation if you’re taking a strain that isn’t already present in large quantities in your gut.
“I don’t typically recommend probiotic supplements,” Freuman says. “There is such limited evidence that they do much of anything to change the microbiome in a meaningful way or contribute to enhanced gut health for most people.”
The evidence for postbiotic supplements is even more limited. “We don’t have enough information on the safety or efficacy of postbiotic supplements at this time,” Guizar says.
Freuman explains that a prebiotic-rich diet likely supports the existing probiotics in your gut, helping them to thrive. “If you are truly interested in diversifying your gut microbiome and increasing the abundance of health-promoting species, the research strongly supports that high-fiber diets that contain very diverse types of plant-based foods are a much more effective approach,” she says.
DIY, Don’t Buy
The short of it is that there’s really no need to think about postbiotics at all. “There is very little research as to whether taking postbiotics in supplement form does anything to enhance human health,” Freuman says.
That’s not to say that postbiotics aren’t beneficial. We know that these postbiotics are health promoting. But why buy them in supplement form when your body is making them constantly? Part of the benefit of postbiotics likely comes from the prebiotic-postbiotic interaction—the breaking down of ingested prebiotics by health-promoting probiotics, which in itself can help you digest fiber more comfortably. You won’t reap this benefit from a postbiotic supplement. Weinstock adds that many postbiotics are volatile and difficult to preserve on the supplement shelf.
“A much surer way to secure the health benefits of these postbiotics is to simply eat a healthy, diverse, fiber-rich diet,” Freuman says.
If you’re excited about microbiome research and the potential uses and benefits of prebiotics, probiotics, and postbiotics, great. So are the researchers and clinicians who study them. But spending lots of time and money on supplements right now is jumping the gun.
“There’s this huge amount of work that has to go into studying our tissues, metabolites, microbes, all of that, to try and correlate them with all different types of diseases,” Weinstock says. Much of what’s being studied, like the effect of the microbiome on neurodegenerative diseases like Parkinson’s and Alzheimer’s, will take years to figure out, because these conditions manifest very slowly over time and have to do with things happening inside the body at extremely low levels. Weinstock is hopeful and excited about all of this. “We already have all of these microbes inside of us. We just need to figure out how to access them, how to use them,” he says. But it will take time before we can come to any real, actionable conclusions.
Ultimately, the vague potential of various microbes and their metabolites might be what drives such fanatical interest in them. “People want to feel like they have influence over their health,” Guizar says. No matter that probiotic and postbiotic supplements haven’t been shown to offer any substantial benefit for healthy people, or that the best way to get prebiotics is to eat the same nutritious diet that’s been recommended for decades. There’s so much we don’t know about these microbes. And for many, it’s hard to resist the idea that maybe, just maybe, a certain pill or specific supplement might have benefits beyond what the science currently understands.