Few areas of nutrition science suffer more terminological drift than this one. “Probiotic” is printed on kombucha and dog food alike; “prebiotic” is used as a synonym for fiber; “postbiotic” is new enough that the marketing has outrun the meaning. Each, in fact, has a formal definition arrived at by expert consensus panels convened by the International Scientific Association for Probiotics and Prebiotics (ISAPP). Used correctly, they are not interchangeable.

Probiotic

The 2014 ISAPP consensus defines a probiotic as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” Three load-bearing clauses follow: the organisms must be live, the dose must be adequate (strain-specific, and defined by the evidence for that strain), and a benefit must be demonstrated. A genus on a label — “contains Lactobacillus” — satisfies none of these on its own.

Prebiotic

The 2017 ISAPP consensus defines a prebiotic as “a substrate that is selectively utilized by host microorganisms conferring a health benefit.” Note what this excludes: not all fiber is prebiotic, and the category is not limited to carbohydrates. The defining test is selective utilization by the resident community to a documented benefit.

Postbiotic

The newest term. The 2021 ISAPP consensus defines a postbiotic as “a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.” The key word is inanimate: a postbiotic is not alive. That is precisely what distinguishes it from a probiotic, and it is the clause most often violated in marketing.

Live and beneficial (probiotic); a substrate selectively used by microbes (prebiotic); a non-living microbial preparation that benefits the host (postbiotic). The benefit clause is mandatory in all three.

The discipline these definitions impose is the point. A product that cannot point to a defined strain, an adequate dose and an outcome is, by the field’s own consensus, not entitled to the word.

Frequently asked

What is the difference between a prebiotic and a probiotic?

A probiotic is live microorganisms that confer a health benefit at an adequate dose. A prebiotic is a non-living substrate (often, but not only, a fiber) that is selectively used by your resident microbes to produce a benefit. One adds organisms; the other feeds the ones already there.

Are postbiotics the same as probiotics?

No. By the 2021 ISAPP consensus a postbiotic is a preparation of inanimate (non-living) microorganisms or their components. The defining difference from a probiotic is that a postbiotic is not alive.

Can you take prebiotics and probiotics together?

Yes; a formulation combining the two is termed a synbiotic. Whether a given combination delivers a benefit depends on the specific strain, the specific substrate and the evidence for that pairing — not on the combination in the abstract.

Sources

  1. Hill et al., ISAPP consensus on the term “probiotic,” Nature Reviews Gastroenterology & Hepatology (2014)
  2. Gibson et al., ISAPP consensus on the definition of prebiotics, Nature Reviews Gastroenterology & Hepatology (2017)
  3. Salminen et al., ISAPP consensus on the definition of postbiotics, Nature Reviews Gastroenterology & Hepatology (2021)
Editorial content for general information only — not medical advice, diagnosis or treatment. Talk to a qualified clinician about your own health.