“Probiotics, prebiotics, and postbiotics are so critical to our gut health, and so much of our immune [function] and overall health is tied to our gut microbiome,” Rosales says. “I don’t think many people realize that, or how they can modify their microbiome.”

There’s also a lot for consumers to learn, experts say, because there’s widespread confusion about these biotics—including what they are, where to find them, and what they can or can’t do. 

What’s in a name: probiotics

Probiotics, probably the best-known of the three players, are defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP), as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” In this case, you are the host, the person who consumes them. And the “live microorganisms” are usually bacteria that have a health-promoting effect. Given that there are good bacteria and bad bacteria in the human body, the goal is to ingest probiotics that keep the bad ones in check.

Besides promoting general gut health, consuming food rich in probiotics can improve irritable bowel syndrome and antibiotic-related diarrhea, prevent traveler’s diarrhea, produce vitamins and increase nutrient absorption, and decrease the risk of common infections. In fact, when consumed regularly, probiotics have been found to reduce the occurrence of upper respiratory tract infections (like the common cold), according to research in a 2022 issue of The Cochrane Database of Systematic Reviews. 

Many different types of beneficial bacteria are considered probiotics. The most common ones include Lactobacillus and Bifidobacterium, of which there are dozens of strains. “You have to match what it is you’re concerned about with the probiotic you should use,” says Gregor Reid, a microbiologist and distinguished professor emeritus at Western University in London, Ontario. In other words, if you consume a strain shown to improve constipation and you’re taking it in the hope that it will reduce your blood sugar, you’re likely to be disappointed, Reid says. (A knowledgeable health-care professional can make specific recommendations about which strains to consume.)

Some foods, such as yogurt, kefir, kimchee, and fermented soybeans and kombucha naturally contain probiotics, Rosales says. But here’s where things get complicated: Not all fermented foods or yogurts contain probiotics, Reid says. As a consumer, a good starting point is to look for the phrase “contains live and active cultures” on the label; it’s even better if specific strains of bacteria are listed, because then you’ll know you’re getting the right stuff.

In other instances, specific strains of probiotics are added to various “functional foods”—which are defined as having benefits, beyond simply providing nutrients, thanks to the addition of other ingredients. Such foods include beverages, yogurts, and cereals; probiotics are also available as supplements.

“The challenge with probiotics is they have to arrive live and well in your gut to have a health benefit,” Rosales explains. “That’s why we’re seeing them in supplements.”

When choosing functional foods or supplements that contain probiotics, Reid recommends consulting the website USProbioticGuide.com, which is designed to help health-care professionals make decisions about probiotic therapy for patients; there, you’ll find information about specific food products and supplements, the probiotic strains they contain, the health conditions they target, and how to use them.

What’s in a name: prebiotics

Simply put, prebiotics are sources of food for those beneficial microbes—the probiotics—explains Gail Cresci, a nutritionist and gut microbiome researcher in the department of pediatric gastroenterology, hepatology, and nutrition at the Cleveland Clinic.

“They are typically a form of carbohydrate or fiber that we don’t have the enzymes to digest,” she says. As a result, they move through the digestive tract to the intestine, where beneficial bacteria can feast on them.

Research has found that specific prebiotics can improve mineral absorption and blood sugar regulation, hasten digestion, improve immune function, and lower the risk of cardiovascular disease. In a study published in 2021 in the journal Frontiers in Immunology, researchers found that when people with mildly high cholesterol consumed 80 grams (1 cup) of oats daily for 45 days, their total cholesterol and (artery-clogging) LDL cholesterol levels decreased significantly.

The researchers noted that consumption of oats significantly increased the prevalence of bacteria that are known to improve metabolic health; another hypothesis is that the beta-glucans in oats may bind to cholesterol in the small intestine, thereby reducing its absorption.

Meanwhile, a study published in 2021 in the journal Psychopharmacology found that when healthy people consumed a 12.5 gram dietary supplement containing the fiber polydextrose daily for four weeks, their cognitive flexibility and sustained attention during various tasks improved slightly. This may be because consumption of polydextrose improved gut-to-brain communication.

Some vegetables, fruits, and grains—such as onions, garlic, bananas, chicory root, Jerusalem artichokes, asparagus, wheat, barley, oats, and beans—naturally contain prebiotics. They are added to other foods—such as yogurts, cereals, breads, and beverages—to enhance human health.

But you won’t find the word “prebiotic” listed on the label. Instead, you’ll find words such as galactooligosaccarides, fructooligosaccharies, oligofructose, beta-glucans, chicory fiber, or inulin on the ingredients list.

Although there isn’t an official recommended daily intake of probiotics or prebiotics, Reid says, “you probably need to consume five grams of prebiotics to stimulate beneficial microbes in your gut.” 

Prebiotics + probiotics = postbiotics

In a nutshell, postbiotics “are metabolites of the probiotics or other microbes that you’ve ingested,” Reid says. In other words, when you consume foods that are rich in probiotics and prebiotics, the microbes in your gut consume the undigestible prebiotic fiber and produce bioactive compounds called postbiotics. (Postbiotics can also be found in some infant formulas and supplements for adults.)

“They are ultimately the endgame that we want—they affect how our gut operates and keep the good bacteria there and the bad bacteria out,” says Gina Crist, a community health specialist focused on nutrition at the University of Delaware.

Postbiotics have specific physiological benefits in their own right, including anti-inflammatory, antioxidant, and anticarcinogenic properties, Rosales says. “They protect the gut barrier, preventing leaky gut. They help with water and electrolyte absorption in the gut, and they have beneficial effects on immune function.” These are just some of the known effects; more are emerging on a regular basis.

Keep in mind: As is the case with other dietary supplements, probiotic, prebiotic, and postbiotic supplements aren’t regulated by the Food and Drug Administration. Manufacturers “don’t have to prove efficacy or safety,” Cresci notes, which is one reason she and other experts don’t recommend taking these supplements unless it’s under a doctor’s direction.

“In the last 10 years, we’ve realized how important the gut microbiome is to us, the host,” Cresci says. “We feed these microbes every day with what we eat.” The best way to take care of the microbiome and your overall health, she says, is by consuming a healthy diet that’s rich in fruits, vegetables, and fiber and low in fat, sugar, and processed foods. “Taking a probiotic or a probiotic supplement isn’t going to fix a bad diet.”