Probiotics and prebiotics are two terms that often appear together in gut health discussions, but they refer to very different things. Understanding the distinction — and how the two work together — provides a more complete picture of how to approach gut microbiome support through supplementation.
What Are Probiotics?
Probiotics are live microorganisms — bacteria and yeasts — that, when consumed in adequate amounts, confer a benefit to the host. The most commonly supplemented probiotic genera are Lactobacillus and Bifidobacterium, along with the beneficial yeast Saccharomyces boulardii and spore-forming Bacillus strains.
Probiotic supplements introduce live organisms into the gastrointestinal tract. These organisms can temporarily colonize the gut, interact with the existing microbiome, and influence the gut environment in various ways depending on the specific strains used.
For a detailed guide to comparing probiotic supplements, see How to Compare Probiotic Supplements: CFU, Strains, and Delivery.
What Are Prebiotics?
Prebiotics are non-digestible dietary compounds — primarily specific types of fiber and carbohydrates — that selectively feed and support the growth of beneficial microorganisms already living in the gut. Unlike probiotics, prebiotics are not live organisms. They are food for the microbiome.
Common prebiotic compounds include:
- Inulin — A fructan fiber found naturally in chicory root, Jerusalem artichoke, garlic, and onions; one of the most widely used prebiotic ingredients in supplements
- Fructooligosaccharides (FOS) — Short-chain fructans that selectively feed Bifidobacterium and Lactobacillus species; often derived from chicory or synthesized from sucrose
- Galactooligosaccharides (GOS) — Derived from lactose; well-researched for supporting Bifidobacterium growth; used in infant formulas and adult supplements
- Partially hydrolyzed guar gum (PHGG) — A soluble fiber with prebiotic properties and good digestive tolerability
- Resistant starch — Found in cooked and cooled potatoes, green bananas, and legumes; feeds a broad range of beneficial gut bacteria
Key Differences at a Glance
| Feature | Probiotics | Prebiotics |
|---|---|---|
| What they are | Live microorganisms | Non-digestible dietary fiber |
| Found in | Fermented foods, supplements | Plant foods, supplements |
| Common examples | Lactobacillus, Bifidobacterium | Inulin, FOS, GOS, chicory root |
| Supplement formats | Capsules, powder, gummies, liquids | Capsules, powder |
How Probiotics and Prebiotics Work Together
The relationship between probiotics and prebiotics is complementary. Probiotics introduce or reinforce beneficial organisms in the gut; prebiotics provide the fuel those organisms need to thrive and multiply. When combined in a single formula, they are referred to as a synbiotic.
A synbiotic approach — pairing specific probiotic strains with the prebiotic fibers those strains preferentially ferment — is thought to enhance the survival and activity of the probiotic organisms. Some probiotic formulas include a prebiotic fiber, such as inulin or FOS.
Prebiotics and Digestive Tolerance
Prebiotic fibers are fermented by gut bacteria, which produces short-chain fatty acids (SCFAs) — beneficial compounds that serve as fuel for colonocytes (the cells lining the colon). However, fermentation also produces gas, which can cause bloating or discomfort in some people, particularly at higher doses or when starting supplementation.
If you are new to prebiotic supplementation, starting with a lower dose and gradually increasing over several weeks allows the gut microbiome to adapt and typically reduces initial digestive discomfort.
Do You Need Both?
For most people who consume a varied diet with adequate fiber from vegetables, fruits, legumes, and whole grains, dietary prebiotic intake is reasonable. Prebiotic supplementation is most relevant for those with low dietary fiber intake or those specifically looking to support their probiotic supplementation protocol.
Probiotic supplementation is a separate consideration and is not dependent on prebiotic supplementation to be effective — though the combination may offer additional benefit for some individuals.
Explore Probiotic Supplements
Browse our full selection of Probiotic supplements from established supplement brands including Metagenics, NOW Foods, Genestra Brands, Pure Encapsulations, and Douglas Laboratories. Many of our probiotic formulas include prebiotic fibers for a synbiotic approach.