When you walk into the grocery store, it seems probiotics are everywhere.
Yogurt, sauerkraut, kimchi and kefir are all packed with probiotics, microorganisms that help support healthy bacteria in the digestive system.
But it's not just probiotics that boost digestion and the immune system. There are also their little-known cousins: prebiotics, postbiotics and synbiotics.
The terms all sound similar, but experts warn they are not interchangeable.
While probiotics are active microbes that add to the gut's healthy community of bacteria, prebiotics are plant fibers that 'feed' those good bacteria.
Postbiotics, meanwhile, are made from non-living microorganisms and cell fragments, while synbiotics serve as a combination of prebiotics and postbiotics.
So what does each one do, and how much, if any, does your gut really need?
Below, dietitians reveal to the Daily Mail everything you need to know about these powerful microbes.
Probiotics, prebiotics and postbiotics all sound similar, but they are not created equal
Prebiotics: Feeding the microbes you already have
'Prebiotics are the fuel for the good bacteria in the gut,' Leslie Bonci, a registered dietitian in Pittsburgh, told the Daily Mail.
Prebiotic compounds are naturally found in a variety of plant-based sources, including onions, garlic, leeks, asparagus, oats, lentils, whole grains, flaxseed, apples and green bananas.
By helping healthy bacteria multiply, prebiotics are thought to support the gut barrier and protect colon cells from damage.
A 2024 systematic review and meta-analysis of randomized trials found that supplementation with fructooligosaccharides, a type of prebiotic most often found in chicory root and garlic, increased bowel-movement frequency and improved constipation.
Frequent bowel movements keep stool from sitting in the colon for too long and raising the risk of toxins entering the colon.
But adding too much too quickly can backfire. 'Some people find that taking a supplemental form of prebiotics can cause a lot of digestive distress,' Bonci said.
She recommends gradually increasing fiber and food sources of prebiotics rather than immediately reaching for a supplement, as the dosage can vary.
Probiotics: Not all strains are created equal
Probiotics are live microorganisms that can boost the gut's population of healthy bacteria, but each kind works differently.
'Different strains can have different effects, and the research supporting one strain for a particular condition doesn’t necessarily apply to another,” Amanda Godman Roll, a dietitian based in New York, told the Daily Mail.
The American Gastroenterological Association emphasizes that not all strains work for all conditions. For example, its guidelines have found insufficient evidence to broadly recommend all probiotics for several digestive conditions, including irritable bowel syndrome (IBS).
That doesn't mean they never help, but their benefits are highly individual.
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.
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