Prebiotics vs Probiotics for Gut Health: What’s the Difference?

Probiotics are live microorganisms, such as certain bacteria and yeasts, that can provide a health benefit when taken in adequate amounts. Prebiotics aren't alive: they're substances, typically certain carbohydrates such as some types of fiber, that the microorganisms already living in your gut use as food in ways linked to a health benefit. In short, probiotics add microorganisms, while prebiotics feed some of the ones you already have. Neither is better in general. What fits depends on your goal, your diet and the evidence for a specific food or product.

Prebiotics vs Probiotics at a Glance

What Are Prebiotics?

A scientific panel convened by the International Scientific Association for Probiotics and Prebiotics (ISAPP) defines a prebiotic as "a substrate that is selectively utilized by host microorganisms conferring a health benefit." Two parts of that definition matter:

• Selective use. A prebiotic is used by particular microorganisms, not by gut bacteria in general.
• A documented benefit. The panel states that a health benefit must be documented for a substance to be considered a prebiotic.

Most prebiotics are carbohydrates that the body doesn't digest on its own. Mayo Clinic (opens in a new tab) describes them as parts of food that the body doesn't digest but that may be used by microorganisms, found mainly in high-fiber foods. Common prebiotic supplement ingredients include inulin and fructo-oligosaccharides (FOS).

Under this definition, fiber and prebiotics aren't the same thing. Fiber is a broad category, and a fiber counts as a prebiotic only if it meets the selective-use and health-benefit criteria. For background on fiber in general, see our guide to fiber and bloating.

What Are Probiotics?

The definition most experts use, also from an ISAPP panel and quoted by the NIH Office of Dietary Supplements (opens in a new tab) (ODS), describes probiotics as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host."

According to ODS, probiotic products commonly contain microorganisms from groups such as Bifidobacterium, members of the family Lactobacillaceae, Saccharomyces (a yeast), Streptococcus and Bacillus. Each probiotic is identified by its strain, which includes the genus, the species, a subspecies if applicable and a strain designation.

Strain matters because probiotics aren't interchangeable. NCCIH (opens in a new tab) notes that different types of probiotics may have different effects, so research on one strain doesn't necessarily apply to another. ODS also cautions that not all foods and supplements labeled as probiotics have proven health benefits.

How Prebiotics and Probiotics Work Differently

The basic difference is what each one adds:

• A probiotic adds microorganisms from outside. Its effects depend on the specific strain and the situation it's used in.
• A prebiotic adds food for microorganisms that are already there. It is used selectively by some of them, rather than by gut bacteria in general.

Because gut bacteria ferment prebiotics, more prebiotic intake can mean more gas, particularly at first. Probiotics can also cause mild digestive symptoms in some people.

Prebiotic Foods vs Probiotic Foods

Prebiotic foods are mostly plant foods rich in fermentable fiber. Cleveland Clinic (opens in a new tab) lists sources of resistant starch such as green bananas, oats, barley, rice, beans and legumes, and boiled potatoes that have been cooled, as well as pectin in fruits such as raw apples. These foods also provide other nutrients.

Probiotic foods are less straightforward than they sound. ODS notes that yogurt may contain probiotics, and that some foods, such as certain milks and cereals, have probiotics added. But it also cautions that not all fermented foods that contain live cultures have probiotic microorganisms. Many cheeses, kimchi, kombucha, sauerkraut, miso and pickles typically don't contain strains with proven probiotic benefits, even though they're fermented.

In other words, "fermented" and "probiotic" aren't the same thing. A fermented food can still be part of a healthy diet without being a proven probiotic. Our guides to foods that help with bloating and foods that cause bloating cover how some of these foods affect digestive comfort.

Prebiotic Supplements vs Probiotic Supplements

Prebiotic supplements usually contain one or a few isolated ingredients, such as inulin or FOS, in powders, capsules, tablets or gummies. Some fiber supplements are marketed as prebiotics. A label that uses the word "prebiotic" doesn't by itself show that the ingredient, in that amount, meets the scientific definition or has a documented benefit.

Probiotic supplements contain one or more strains of live microorganisms. ODS says many contain 1 to 10 billion colony-forming units (CFU) per dose, and some contain 50 billion or more. Because they're alive, their count can decline over time, and storage conditions matter. NCCIH also reports that some probiotic products have been found to contain microorganisms other than those listed on the label.

Prebiotic and probiotic products sold in stores are generally dietary supplements or foods, and the FDA (opens in a new tab) doesn't approve dietary supplements for safety and effectiveness before they're sold. For a broader checklist, see Digestive Health Supplements: What to Look for Before You Buy.

Can Prebiotics or Probiotics Cause Gas or Bloating?

They can, although it doesn't happen to everyone, and the reasons differ.

Prebiotics. Fermentation by gut bacteria produces gas. Cleveland Clinic notes that adding prebiotic foods quickly can leave you feeling bloated or gassy, and advises a gradual introduction. NIDDK (opens in a new tab) similarly notes that adding fiber slowly, by 2 to 3 grams a day, may help prevent gas and bloating. Some people with irritable bowel syndrome (IBS) find certain fermentable carbohydrates hard to tolerate. NIDDK describes a low-FODMAP diet (opens in a new tab) that a doctor may suggest for IBS, which limits some of these carbohydrates for a period of time.

Probiotics. ODS says probiotics are unlikely to cause harm in healthy people and that side effects are usually minor, typically self-limited digestive symptoms such as gas.

Gas or bloating after starting a prebiotic or probiotic doesn't tell you what's causing your symptoms in general. If bloating is frequent, severe, new or comes with other symptoms, it's worth talking with a doctor rather than adjusting supplements on your own. Our guide to probiotics for bloating looks at the evidence on bloating specifically.

What Are Synbiotics?

Products that contain both a probiotic and a prebiotic are often called synbiotics. In 2020, an ISAPP panel defined a synbiotic as "a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host."

As summarized by ISAPP (opens in a new tab), the panel described two types:

• Complementary synbiotics combine an established probiotic with an established prebiotic. Each component must meet the minimum criteria for a probiotic or a prebiotic, and the combined product must be shown to provide a health benefit.
• Synergistic synbiotics contain a substrate designed to be selectively used by the microorganisms given with it. Their components don't have to qualify individually as a probiotic or a prebiotic, but a study must show both that selective use and a health benefit.

In everyday marketing, "synbiotic" often just means a product contains both a probiotic and a prebiotic ingredient. The scientific definition is stricter because it requires a health benefit. A label that combines the two doesn't by itself show that the combination has been tested.

Which Is Better: Prebiotics or Probiotics?

Neither is better overall. They do different things, and the evidence depends on the specific strain, ingredient, amount and use. A few questions can help you think it through:

• What's your goal? For a specific health concern, look for evidence on the specific strain or ingredient for that use, and ask a healthcare provider.
• What does your diet look like? Fiber-rich plant foods provide prebiotic fibers along with other nutrients. If you add more of them, do it gradually.
• What does the product actually contain? A probiotic that names its strains and a prebiotic that names its ingredient and amount can be checked against research. Vague labels can't.
• How do you tolerate them? Prebiotics in particular can cause gas, especially when intake increases quickly.

How to Read a Supplement Label

Food First or Supplement?

Both approaches have a place, and they aren't equivalent.

Food provides prebiotic fibers along with vitamins, minerals and other nutrients, and it's how most people get prebiotics. Fermented foods can be part of a varied diet, even when they don't contain proven probiotic strains. Mayo Clinic notes that most healthy adults can safely add foods containing probiotics and prebiotics to their diets.

Supplements provide specific ingredients in defined amounts, which matters when research on a particular strain or ingredient is relevant to you. They aren't approved by the FDA for safety and effectiveness before sale, and NCCIH reports that some probiotic products haven't matched their labels.

In our editorial view, a balanced approach is to get prebiotic fibers from a varied diet and to choose any supplement for a specific reason, after discussing it with a healthcare provider. For other everyday approaches to digestive comfort, see What Helps With Bloating and Slow Digestion?.

What the Evidence Actually Says

Safety Considerations

• Healthy adults. ODS says probiotics are unlikely to cause harm in healthy people, with side effects usually limited to minor digestive symptoms. Prebiotics can cause gas and bloating, especially when intake rises quickly.
• People who are seriously ill or immunocompromised. ODS notes that probiotics have been linked to bloodstream infections, mostly in people who are severely ill or have weakened immune systems. NCCIH advises talking with a healthcare provider before taking a probiotic supplement, especially if you have health problems.
• Premature infants. Mayo Clinic reports cases in which probiotics given to premature infants caused serious or fatal infections.
• Digestive symptoms. NIDDK (opens in a new tab) advises talking with your doctor before using probiotics for gas symptoms.
• Pregnancy, breastfeeding, medicines or health conditions. Ask a healthcare provider before starting a new supplement.

A supplement isn't a substitute for medical care. Persistent, severe or new digestive symptoms are worth discussing with a doctor.

The Bottom Line

Probiotics are live microorganisms, and prebiotics are substances that feed some of the microorganisms already in your gut. Both are defined by a health benefit, so not every fermented food is a probiotic and not every fiber is a prebiotic. Effects depend on the specific strain or ingredient, the amount and the person. Neither is better in general.

If you're deciding between them, start with your goal and your diet. Fiber-rich foods provide prebiotic fibers along with other nutrients. If you consider a supplement, choose one that names its strains or ingredients and amounts, and check for research on those specifics. Talk with a healthcare provider first if you have a health condition, are pregnant or breastfeeding, or take medicines.