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The difference in prebiotic vs probiotic comes down to living versus food. Probiotics are live microorganisms that provide a health benefit when taken in adequate amounts. Prebiotics are not alive: they are substances, mostly certain fibers, that microbes already in your gut use selectively in a way that benefits you. A synbiotic combines live microbes with such a substrate, and a postbiotic is made of microbes that have been deliberately inactivated. These definitions come from consensus panels of the International Scientific Association for Probiotics and Prebiotics (ISAPP).
Peptide Labs sells a few gut-health supplements, and we mention two below. This article is general information, not medical advice. For more depth, see our guides to probiotics for women (strain labels and CFU) and prebiotic fiber supplements (inulin, FOS and tolerance).
Key Takeaways
- Probiotics are live microbes; prebiotics are substances, mostly fibers, that your own gut microbes use.
- Synbiotics pair live microbes with a substrate; postbiotics are inactivated microbes or their parts.
- Not every fermented food contains live microbes, and fermented foods are not automatically probiotics.
- Probiotic effects are strain-specific, and expert guidelines find the evidence thin for many uses.
- Prebiotics can cause gas and bloating; people who are seriously ill or immunocompromised should ask before using probiotics.
Prebiotic vs probiotic: the definitions
ISAPP panels have published four definitions that researchers and many regulators now use:
| Term | ISAPP definition (short form) | Year | Examples on labels |
|---|---|---|---|
| Probiotic | Live microorganisms that, in adequate amounts, confer a health benefit on the host | 2014 | Lactobacillus, Bifidobacterium, Bacillus strains |
| Prebiotic | A substrate selectively used by host microorganisms that confers a health benefit | 2017 | Inulin, FOS, GOS, XOS |
| Synbiotic | A mixture of live microorganisms and substrate(s) selectively used by host microorganisms that confers a health benefit | 2020 | A probiotic strain plus inulin or XOS |
| Postbiotic | A preparation of inanimate microorganisms and/or their components that confers a health benefit | 2021 | Heat-inactivated bacterial strains |
The key word for prebiotics is selectively. Most fiber is good food in general, but a prebiotic has to be used by particular beneficial microbes and be linked to a measurable benefit. Likewise, a live microbe is only a probiotic if a benefit has been shown for that strain.
Probiotics vs prebiotics in food
Fermented foods such as yogurt, kefir, sauerkraut, kimchi and miso are the usual food sources of live microbes. In 2021 an ISAPP panel defined fermented foods as foods made through desired microbial growth and enzymatic conversions, and it drew a clear line between fermented foods and probiotics. Many fermented foods are baked, pasteurized or filtered after fermentation, so they may contain few or no live microbes, and even foods with live cultures are not probiotics unless the specific strains have shown a benefit. On yogurt and kefir, look for wording such as live and active cultures.
Prebiotic fibers are found in plant foods. Inulin, the most common one, occurs in chicory root, artichokes, asparagus, bananas, garlic, leeks, onions, oats, soybeans and wheat. Eating a range of these foods supplies fiber whether or not you take a supplement.
Supplement forms
- Probiotic capsules and powders list microbes by genus, species and strain, with a count in colony-forming units (CFU). The FDA requires quantity by weight and allows CFU as well.
- Probiotic gummies often use spore-forming Bacillus strains, which tolerate the heat of gummy manufacturing better than many other bacteria.
- Prebiotic powders, gummies and capsules list the fiber in grams, such as inulin, chicory root fiber, FOS, GOS or XOS.
- Combination products may add a prebiotic, a postbiotic or other ingredients to a probiotic.
Synbiotics: probiotics and prebiotics together
The 2020 ISAPP synbiotic statement describes two kinds. A complementary synbiotic is a probiotic plus a prebiotic, each of which should work on its own. A synergistic synbiotic is designed so that the added substrate is used by the microbe it comes with. Simply putting a strain and a fiber in the same capsule does not prove the combination has a benefit; that depends on evidence for the product.
Pendulum Akkermansia is one example of a live microbe paired with a prebiotic fiber: the brand lists live Akkermansia muciniphila with chicory inulin in a one-capsule serving and says the product has not been studied in pregnancy or breastfeeding. Our Akkermansia guide covers what trials of this microbe have measured.
Postbiotics: inactivated microbes
Postbiotics are microbes that have been deliberately inactivated, usually by heat, with or without the substances they produced. Under the 2021 ISAPP definition, a purified metabolite on its own does not count as a postbiotic; the preparation must contain inactivated cells or cell parts. Because nothing needs to stay alive, postbiotics are less sensitive to storage conditions than live probiotics.
Goli Pre Pro Postbiotic Gummies combine all three categories on one label: the spore-forming probiotic Bacillus subtilis DE111, the prebiotic fiber XOS (xylooligosaccharides) and Lacticaseibacillus paracasei MCC1849, which the brand lists as the postbiotic. As with any combination, the label shows what is in it, not that the mix has been tested as a whole.
What the evidence shows
Research on both sides is uneven. The U.S. National Center for Complementary and Integrative Health notes that effects differ from one strain to another, so results for one Lactobacillus do not transfer to another. In its 2020 guidelines, the American Gastroenterological Association reviewed probiotics for eight digestive conditions; only four had enough data for conditional recommendations, and for the others, including irritable bowel syndrome, the panel advised using probiotics only within clinical trials because of knowledge gaps.
For prebiotics, a 2018 meta-analysis of 64 randomized trials in 2,099 healthy adults found that fiber, especially inulin-type fructans and GOS, raised levels of Bifidobacterium and Lactobacillus. Changes in gut bacteria are not the same as a proven health benefit, and results for weight and blood sugar have been weaker.
| Probiotics | Prebiotics | |
|---|---|---|
| What they are | Live microorganisms | Substances, mostly fibers, used by resident microbes |
| What studies measure | Specific outcomes for specific strains | Changes in gut bacteria, stool habits |
| Main evidence caveat | Strain-specific; many conditions lack strong data | Microbe shifts do not always mean a health benefit |
| Common side effects | Usually mild digestive symptoms | Gas and bloating, especially at first |
| Storage | Viability falls with heat and moisture | Stable at room temperature |
How to read probiotic and prebiotic labels
- Strain names. A probiotic should list genus, species and a strain code, such as Bacillus subtilis DE111.
- CFU through expiration. A count guaranteed through the end of shelf life is more useful than one “at time of manufacture.”
- Fiber type and grams. A prebiotic should name the fiber and give grams per serving.
- Postbiotic wording. Look for a named strain that has been inactivated, not just “fermentation extract.”
- Sugar and allergens. Gummies may contain added sugar or sugar alcohols; check allergen and shared-facility statements.
- Storage directions. Follow them, especially for live products.
Safety: who should be careful
- People with severe illness or weakened immune systems face a higher risk of harmful effects from probiotics, according to NCCIH, and should ask a doctor first.
- The FDA has warned about serious infections in premature infants given probiotic products.
- NCCIH notes that some probiotic products have contained microbes other than those on the label.
- Prebiotics such as inulin and FOS are fermentable fibers (FODMAPs) that can cause gas and bloating, and people with irritable bowel syndrome may not tolerate them well.
- Follow the label and ask a healthcare provider if you are pregnant, nursing or take medicines.
You can compare other options in our fiber and gut health category.
Frequently Asked Questions
What is the difference between a prebiotic and a probiotic?
A probiotic is a live microorganism with a shown health benefit. A prebiotic is a substance, usually a fiber, that beneficial microbes already in your gut use selectively.
Should I take probiotics or prebiotics?
It depends on your diet and health. Many people get prebiotic fiber from plant foods and live microbes from some fermented foods. Ask a healthcare provider before starting a supplement.
What is a synbiotic?
A synbiotic is a mixture of live microorganisms and a substrate used by gut microbes that provides a health benefit, as defined by ISAPP in 2020.
What is a postbiotic?
A postbiotic is a preparation of inactivated microorganisms or their components that provides a health benefit. Purified metabolites alone do not qualify.
Are fermented foods probiotics?
Not automatically. Some fermented foods contain no live microbes after processing, and live cultures only count as probiotics if those strains have shown a benefit.
Can prebiotics cause gas?
Yes. Prebiotic fibers are fermented by gut bacteria, so gas and bloating are common, especially when starting. People with IBS may be more sensitive.
Questions about a label? Contact us or read our Buyer’s Guide. Follow the label and ask a healthcare provider before starting any supplement. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed September 2026.
Related guides: Prebiotic Fiber Supplements: Inulin, FOS and What the Research Shows, Probiotics for Women: How to Read Strains, CFU and Probiotic Gummy Labels, Digestive Health Supplements: Fiber, Probiotics, Prebiotics and Enzymes Explained, Best Probiotic? How to Choose a Probiotic by Strain, CFU and Evidence, When to Take Probiotics: Timing, How Long They Take and Side Effects, Kombucha Benefits: What Human Studies Show, Risks, and Gummies vs the Drink, How to Improve Gut Health: Evidence-Based Habits and What Tests Can’t Tell You.