Probiotics and prebiotics sound almost the same, show up together on many labels and are easy to mix up. They are not the same thing: one is live microorganisms and the other is the food the microorganisms in your gut use. This guide explains each one using the definitions from the International Scientific Association for Probiotics and Prebiotics (ISAPP) and information from the National Institutes of Health Office of Dietary Supplements (NIH ODS), and it helps you read a label before you buy.

What probiotics are, according to the current scientific definition

Probiotics are live microorganisms that, in adequate amounts, provide a health benefit to the person who takes them. That is the definition an ISAPP expert panel reaffirmed in 2014 as current and broad enough for its uses (Hill et al., 2014). NIH ODS explains that they are mostly bacteria, though some are yeasts, and that they are found in some fermented foods such as yogurt, in foods they are added to, and in supplements (NIH ODS, 2025).

NIH ODS adds an important caveat: not all foods or supplements labeled as probiotics have proven health benefits (NIH ODS, 2025). The word on a label guarantees nothing by itself; what matters is the strain, the amount and the evidence behind it.

Do all fermented foods contain probiotics?

No, not all fermented foods contain probiotics. According to NIH ODS, many fermented foods contain live microbes but not necessarily proven probiotic microorganisms; it names many cheeses, kombucha, sauerkraut and miso among them (NIH ODS, 2025). Some, such as sourdough bread and most commercial pickles, are processed in a way that removes the live cultures (NIH ODS, 2025). Yogurt with live cultures remains one of the best-known sources.

What prebiotics are and where they come from in your diet

Prebiotics are substances that the microorganisms in your body use selectively and that, in doing so, provide a health benefit. That is how ISAPP defined them in its 2017 consensus (Gibson et al., 2017). In practice, the most studied are complex carbohydrates such as inulin and other fructo-oligosaccharides, which gut microorganisms use as fuel (NIH ODS, 2025).

Prebiotics are not microorganisms: they are not alive and cannot "die" in the bottle. Their role is to feed the bacteria that already live in your gut. In a controlled trial of 45 healthy volunteers, eating snack bars with Jerusalem artichoke or chicory inulin, at doses of several grams a day, increased fecal bifidobacteria within three weeks; some participants noticed more gas, mostly mild (Kleessen et al., 2007).

Which everyday foods naturally contain prebiotics?

Several common foods naturally contain prebiotics, mainly inulin and oligofructose. A U.S. Department of Agriculture analysis of data from more than 15,000 people found that the American diet provides an average of 2.6 grams of inulin a day, and that wheat and onions are the main sources: wheat provides about 70% and onions about 25% (Moshfegh et al., 1999). Onion, which goes into almost every sofrito and so many Latin dishes, is an easy ally.

The difference between probiotics and prebiotics, made simple

The easiest way to remember it: probiotics are live microorganisms that reach your gut, and prebiotics are the food those microorganisms use. One is like seeds and the other like fertilizer. Both act on the same community of microorganisms, but in different ways. Neither one replaces a varied diet with vegetables, legumes and whole grains.

What is a synbiotic and why are they combined?

A synbiotic is a mixture of live microorganisms and substances that microorganisms use selectively, which together provide a health benefit. That is how ISAPP defined it in 2020 (Swanson et al., 2020). NIH ODS notes that commercial products containing both probiotics and prebiotics are often called synbiotics (NIH ODS, 2025). The idea behind combining them is simple: the probiotic arrives together with fiber your gut flora can use.

Can you take probiotics and prebiotics together?

Yes, you can take probiotics and prebiotics together, and many products combine them. When starting prebiotic fiber, some people notice more gas for the first few days, as seen in the inulin study (Kleessen et al., 2007). NIH ODS describes the side effects of common probiotics as usually minor and short-lived, such as gas (NIH ODS, 2025).

What is a postbiotic and how is it different?

A postbiotic is a preparation of dead microorganisms, whole or in fragments, with or without the substances they produce, that provides a health benefit. NIH ODS says not to confuse them with probiotics, which must be alive (NIH ODS, 2025). It is a newer term you will see more often on labels and in articles. The practical difference is simple: the probiotic is alive, the prebiotic is food for your gut flora, and the postbiotic is the inactive microorganism or what it produces.

How to read a probiotic label before you buy one

A probiotic label tells you more than it seems, if you know what to look for. These are the three key points, according to NIH ODS.

What do CFU mean on a probiotic label?

CFU stands for colony-forming units, the number of live cells the label declares. Many supplements contain 1 to 10 billion CFU per dose, but NIH ODS makes clear that a higher number does not mean the product is more effective (NIH ODS, 2025). It also recommends looking for products that state the CFU at the end of their shelf life, not only at the time of manufacture, because probiotics can lose viability over time (NIH ODS, 2025).

Why does the probiotic strain matter so much?

The strain matters because the effects of probiotics can be specific to each one. A probiotic is identified by its genus, its species and a strain designation of letters and numbers, and NIH ODS says recommendations for use should be strain-specific (NIH ODS, 2025). That is why a good label does not just say "Lactobacillus": it gives the full name, for example Lactobacillus acidophilus LA85.

Are probiotics safe for everyone to take?

For most healthy people, common probiotics are unlikely to cause harm. NIH ODS explains that a few cases of serious infection have been reported, almost always in people who were very ill or had weakened immune systems, and that FDA warned in 2023 about the risks for premature infants (NIH ODS, 2025). If you are pregnant, have a medical condition or take medication, check with your healthcare professional first.

How GUT combines a probiotic and prebiotic fiber in one formula

If you want both in a single step, GUT brings them together: a probiotic and prebiotic fiber that support a balanced gut flora.* Its label names the full strain, Lactobacillus acidophilus LA85, and the fiber, inulin from Jerusalem artichoke, with the amount of every ingredient in plain sight. GUT combines prebiotic, probiotic and digestive enzymes in one formula,* in two capsules a day, and supports easy, comfortable digestion, every day.*

GUT is $49.90 a month with a subscription and free shipping, and you can skip, pause or cancel before your next charge. Your first bottle has a 30-day money-back guarantee from delivery. Meet GUT, check its ingredients and certificate of analysis, or read our guide to bloating after eating.

Frequently asked questions about probiotics and prebiotics

What is the difference between probiotics and prebiotics?

Probiotics are live microorganisms that provide a health benefit in adequate amounts. Prebiotics are substances, such as inulin, that gut microorganisms use as food.

Which is better, a probiotic or a prebiotic?

Neither is better overall: they do different jobs. Probiotics provide live microorganisms and prebiotics feed the ones already living in your gut. That is why many products combine them.

Does yogurt count as a probiotic food?

Yogurt with live cultures is one of the best-known sources of beneficial microbes, according to NIH ODS. Not all fermented foods contain proven probiotics.

Which foods are natural sources of prebiotics?

Wheat and onions are the main sources of inulin and oligofructose in the American diet, according to the U.S. Department of Agriculture.

Does a higher CFU count mean a better probiotic?

No. NIH ODS makes clear that a product with more CFU is not necessarily more effective than one with fewer. The strain and the evidence behind it matter more than the number.

Sources

  • Hill C, Guarner F, Reid G, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology. 2014;11(8):506-514. doi:10.1038/nrgastro.2014.66
  • Gibson GR, Hutkins R, Sanders ME, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology. 2017;14(8):491-502. doi:10.1038/nrgastro.2017.75
  • Swanson KS, Gibson GR, Hutkins R, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of synbiotics. Nature Reviews Gastroenterology & Hepatology. 2020;17(11):687-701. doi:10.1038/s41575-020-0344-2
  • NIH Office of Dietary Supplements. Probiotics: Fact Sheet for Health Professionals. Updated March 25, 2025. ods.od.nih.gov
  • Moshfegh AJ, Friday JE, Goldman JP, Ahuja JK. Presence of inulin and oligofructose in the diets of Americans. The Journal of Nutrition. 1999;129(7 Suppl):1407S-1411S. doi:10.1093/jn/129.7.1407S
  • Kleessen B, Schwarz S, Boehm A, et al. Jerusalem artichoke and chicory inulin in bakery products affect faecal microbiota of healthy volunteers. British Journal of Nutrition. 2007;98(3):540-549. doi:10.1017/S0007114507730751

* 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.

This article is for information only and does not replace advice from a healthcare professional.