Probiotics are live microorganisms, prebiotics are substances that a dog's own resident microbes selectively use, and postbiotics are microorganisms that have been deliberately inactivated, or their components. Each has its own scientific consensus definition, and every one of those definitions includes a health benefit for the host.
What is a probiotic?
A probiotic is made of live microorganisms. The standard definition is "live microorganisms which when administered in adequate amounts confer a health benefit on the host," from the Food and Agriculture Organization of the United Nations and the World Health Organization. An expert panel from the International Scientific Association for Probiotics and Prebiotics (ISAPP) reaffirmed it in a 2014 consensus statement.1
The key word is live. That is what separates a probiotic from the other 2 terms.
What is a prebiotic?
A prebiotic is a substance that a dog's own resident microbes selectively use. ISAPP's 2017 consensus defines it as "a substrate that is selectively utilized by host microorganisms conferring a health benefit."2
The panel states that its definition also applies to prebiotics for animals.2
What is a postbiotic?
A postbiotic is a preparation of microorganisms that have been deliberately inactivated, or their components. An ISAPP panel published that definition in 2021, the newest of the 3: a "preparation of inanimate microorganisms and/or their components that confers a health benefit on the host."3
A postbiotic does not have to come from a probiotic, and the panel notes that the host can include companion animals.3 Researchers have studied inactivated forms of both bacteria and yeasts, such as the yeast Saccharomyces boulardii.3
How do the 3 compare?
| Term | Probiotic | Prebiotic | Postbiotic |
|---|---|---|---|
| What it is | Live microorganisms | A substance a dog's own resident microbes selectively use | Inactivated microorganisms or their components |
| Alive? | Yes | Not a microbe | No, inactivated |
| Definition set by | FAO/WHO, reaffirmed by ISAPP in 2014 | ISAPP, 2017 | ISAPP, 2021 |
How do the 3 fit together?
Each one brings something different. A probiotic adds live microorganisms, a prebiotic is used by the microbes already living in the host, and a postbiotic adds inactivated microorganisms or their components.1,2,3
Because they are different things, a formula that includes all 3 gives you one of each in a single product. Pairing live microorganisms with a substance the host's microbes selectively use even has its own scientific name and definition: a synbiotic.3
How do you spot each one on a label?
Look for each one by name on the label: the prebiotic ingredient, the named probiotic microbe and the named inactivated microbe used as the postbiotic. A 3-in-1 formula should name all 3. They describe different things, so one does not stand in for another.
What should you ask your vet?
Your vet is the best person to help you choose. A few questions make that conversation quicker:
- Which of the 3 fits my dog's age, size and routine?
- Would a formula with all 3 suit my dog?
- What is the best way to add a new chew to my dog's routine?
Seeing the named ingredients and amounts on the label helps your vet give a specific answer.
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Frequently asked questions.
Are prebiotics and probiotics the same thing?
No. Probiotics are live microorganisms. Prebiotics are substances that a dog's own resident microbes selectively use.
Is a postbiotic just a dead probiotic?
Not exactly. Under the 2021 ISAPP definition, a postbiotic is a preparation of deliberately inactivated microorganisms or their components. It does not have to come from a probiotic.
Do the definitions apply to dogs?
Each definition is written around a host rather than people specifically. ISAPP's prebiotic consensus statement adds that the definition applies to animals, and its postbiotic consensus statement notes that the host can include companion animals.
What is a synbiotic?
A synbiotic combines live microorganisms with a substance the host's own microbes selectively use. ISAPP defines it as "a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host."3
Which of the 3 was defined most recently?
Postbiotics. An ISAPP panel published the current definition in 2021, after the 2014 probiotic and 2017 prebiotic consensus statements.
Sources.
- Hill C, 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.
- Gibson GR, 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.
- Salminen S, et al. The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology & Hepatology, 2021.