A trip to the supermarket can make it seem as though probiotics are in nearly every aisle.
Yogurt, sauerkraut, kimchi and kefir are rich in probiotics—microorganisms that help maintain a healthy balance of bacteria in the digestive tract.
Yet probiotics are only part of the picture. Their lesser-known relatives—prebiotics, postbiotics and synbiotics—may also influence digestion and immune health.
Although the names are similar, health experts stress that these substances are not interchangeable.
Probiotics are living microbes that contribute to the gut’s beneficial bacterial population. Prebiotics, by contrast, are plant-based fibers that provide nourishment for those helpful organisms.
Postbiotics come from nonliving microorganisms and their cellular components, while synbiotics combine prebiotics and postbiotics.
What role does each one play—and how much does the average person actually need?
Dietitians explain to Our News Outlet what consumers should know about these increasingly popular gut-health compounds.
Probiotics, prebiotics and postbiotics may sound alike, but each has a distinct role
Prebiotics: Feeding the microbes you already have
“Prebiotics are the fuel that feeds the good bacteria in the gut,” Leslie Bonci, a registered dietitian in Pittsburgh, told Our News Outlet.
These compounds occur naturally in many plant foods, including onions, garlic, leeks, asparagus, oats, lentils, whole grains, flaxseed, apples and green bananas.
By encouraging beneficial bacteria to grow, prebiotics may help strengthen the gut barrier and shield colon cells from damage.
A 2024 systematic review and meta-analysis of randomized trials found that fructooligosaccharides—a prebiotic commonly found in chicory root and garlic—helped increase bowel-movement frequency and ease constipation when used as a supplement.
More regular bowel movements reduce the time stool remains in the colon, potentially limiting the opportunity for toxins to enter colon tissue.
However, introducing too much too fast can cause problems of its own. “Some people find that taking prebiotics in supplement form can cause a lot of digestive distress,” Bonci said.
Rather than starting with a high-dose supplement, she advises gradually adding fiber-rich foods and other prebiotic sources, since recommended amounts can differ from person to person.
Probiotics: Not all strains are created equal
Probiotics are living microorganisms that may increase the gut’s beneficial bacteria, but their effects depend heavily on the specific strain.
“Different strains can have different effects, and research supporting one strain for a particular condition does not necessarily apply to another,” Amanda Godman Roll, a New York-based dietitian, told Our News Outlet.
The American Gastroenterological Association also cautions that no single probiotic approach works for every condition. Its guidelines say there is not enough evidence to recommend probiotics broadly for several digestive disorders, including irritable bowel syndrome, or IBS.
That does not rule out potential benefits, but it does underscore how individual the response to probiotics can be.
Some probiotics have been studied for very specific uses. Lactobacillus rhamnosus GG, or LGG, and Saccharomyces boulardii, a beneficial yeast, have been shown to reduce the risk and symptoms of antibiotic-associated diarrhea.
Bifidobacterium longum 35624, meanwhile, is thought to reduce symptoms of IBS such as bloating and abdominal pain.
Rather than choosing based only on the number of strains or ‘gut healthy’ claims, Godman Roll recommends looking for the exact strain and whether it has been studied at a similar dose for that condition.
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Synbiotics: Combining approaches
Synbiotics are a combination of prebiotics and probiotics, such as yogurt with plant-based toppings
Synbiotics are a combination of probiotics and prebiotics that work together to support bacteria survival and growth.
Common examples include Bifidobacterium and Fructooligosaccharides, as well as Lactobacillus and Inulin.
In food, examples of synbiotics include Greek yogurt with chicory root or a kefir smoothie with bananas and oats.
A 2026 trial of 350 adults with bloating or indigestion found that synbiotic supplementation was associated with improved bloating, gas, abdominal discomfort and other bowel symptoms over six weeks compared to a placebo.
Experts urge consumers to look for evidence on the specific combination in the synbiotic product rather than assuming all synbiotics work the same way.
Postbiotics: Do the microbes need to be alive?
Postbiotics are the newest and perhaps least familiar of these gut-health terms. Unlike probiotics, postbiotics do not contain live microorganisms. Instead, they contain inactivated microbes or parts of those microbes that may still affect the body.
That raises an intriguing question: Can microbes still provide benefits even after they are no longer alive?
Early human research suggests they might. In a 2024 trial of 200 adults with diarrhea-predominant IBS, researchers compared a live strain of Bifidobacterium longum with a heat-treated version of the same strain. Both improved IBS symptom-severity compared to placebo after 12 weeks.
‘The current evidence is limited, but postbiotics are an area of growing interest,’ Godman Roll said. She said research is also exploring their potential role in treating IBS and the bacterial infection Helicobacter pylori (H pylori).
She also noted postbiotics may be of particular interest for some higher-risk populations where giving live microbes can raise concerns, such as those who are immunocompromised.
For consumers, the important distinction is that ‘postbiotic’ is not one ingredient. Different preparations may contain different microorganisms and components, so Godman Roll recommends looking for human research on the exact product or condition you are hoping to address.
So what does your gut actually need?
Fermented foods like kimchi can provide probiotics without needing a supplement
For many healthy people, the answer may be none of these forms as supplements.
Bonci starts with simpler questions: Are you well hydrated? Could your fiber intake be better? Do you regularly eat foods containing live active cultures?
‘I would focus on these variables first before adding in any supplements,’ she said.
Godman Roll takes a similar approach. ‘I would first consider what condition they’re hoping to address and what they’ve already tried,’ she said.
Fermented foods such as yogurt, kefir, sauerkraut and kimchi can provide live microorganisms, while fiber-rich plant foods provide fuel for gut microbes.
There are times when a supplement may be worth considering. Someone taking antibiotics, for example, may benefit from certain probiotic strains that have been studied for antibiotic-associated diarrhea, although probiotics are not appropriate or necessary for everyone.
If constipation is the main concern, total fiber, fluid and the type of fiber may matter more than whether a bottle says ‘prebiotic.’
Ultimately, there isn’t a one-size-fits-all answer. The better question may not be which ‘biotic’ is best, but what problem are you trying to solve?
Johannah Katz, MA, RD, is a registered dietitian based in Florida
