Glossary · Nutrition and probiotics
Probiotic
In one sentence
A probiotic is a live microorganism that, when administered in adequate amounts, confers a health benefit on the host. This is the FAO/WHO definition, retained by the ISAPP consensus panel in 2014.
Also known as: probiotic bacteria · probiotic strain · probiotic supplement
What is a probiotic?
The working definition comes from an FAO/WHO expert group (2001-2002). In 2014 a panel convened by the International Scientific Association for Probiotics and Prebiotics (ISAPP) reviewed it and kept it, with a minor grammatical tweak (Hill et al., Nat Rev Gastroenterol Hepatol). It has three conditions: the microorganism must be alive when given, in an adequate amount, and with a demonstrated health benefit in the host.
That excludes several things often marketed as probiotics: dead microbes or their fragments (covered by the concept of a postbiotic), fermented foods without characterised strains, and faecal microbiota transplantation, which the panel treated as a separate category.
Why the strain matters
A probiotic is named by genus, species and strain, for example Lacticaseibacillus rhamnosus GG. The strain label matters because strains of the same species can behave differently. Most products use members of the Lactobacillus group (reclassified into several genera in 2020), Bifidobacterium, Streptococcus thermophilus or the yeast Saccharomyces boulardii.
Proposed mechanisms include competing with pathogens, producing organic acids, interacting with the immune system and supporting the gut barrier. A plausible mechanism is not proof of clinical benefit; that has to be shown in trials in the relevant population and indication.
What the evidence says
The evidence is uneven. Certain strains have supportive trials and meta-analyses for specific uses, such as antibiotic-associated diarrhoea, although results vary. For many other uses, including mental health or metabolic outcomes, the data are preliminary. Probiotics are generally well tolerated, but rare cases of bacteraemia or fungaemia have been reported in severely immunocompromised people or those with central lines, so use in these groups needs clinical judgement.
Probiotics do not need to colonise the gut permanently; many strains are detectable only while they are being taken.
Example
A community pharmacist is asked which probiotic to take during a course of antibiotics. Rather than treating “probiotics” as a single group, she checks whether the product lists the full strain, states the number of colony-forming units stated for the end of shelf life (not just at manufacture), and whether that strain has trials for antibiotic-associated diarrhoea. She advises the customer to raise it with the prescriber if they are immunocompromised.
Probiotics and Xenogene
Xenogene does not sell probiotics or recommend specific products. A gut microbiota analysis describes the composition of the microbiota, including genera such as Lactobacillus and Bifidobacterium, but it does not by itself tell anyone which probiotic to take or predict how they will respond. That decision rests with the healthcare professional, who may use the result as context. The blog looks at weighing the evidence for probiotics, prebiotics and other supplements in clinical practice.
Frequently asked questions
Do all probiotics do the same thing?
No. Effects depend on the specific strain, dose, formulation and condition studied, and results for one product should not be transferred to another. Look for full strain identification and for trials supporting that particular use.
Should I take probiotics after antibiotics?
There is no blanket recommendation. Some strains have been studied for reducing antibiotic-associated diarrhoea, with mixed results, but probiotics cannot be said to speed up microbiota recovery in everyone. It is a decision to discuss with a healthcare professional.
Are yoghurt and kefir probiotics?
They are fermented foods containing live microbes, but they only count as probiotics if they contain defined strains with a demonstrated benefit at a sufficient dose. The 2014 ISAPP consensus made an exception for yoghurt cultures, given their effect on lactose digestion.
Related terms
- Prebiotic
A prebiotic is a substrate that is selectively utilised by host microorganisms and confers a health benefit, according to the 2017 consensus definition of the International Scientific Association for Probiotics and Prebiotics (ISAPP).
- Postbiotic
A postbiotic is a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host, as defined by the 2021 ISAPP consensus. Purified microbial metabolites alone do not qualify.
- Synbiotic
A synbiotic is a mixture of live microorganisms and substrates selectively utilised by host microorganisms that confers a health benefit on the host, according to the 2020 ISAPP consensus.
- Microbiota
The microbiota is the community of living microorganisms (bacteria, archaea, fungi, protozoa) that inhabits a specific site of the body, such as the gut, mouth, skin or vagina.
- Lactobacillus
Lactobacillus is a genus of Gram-positive, lactic acid-producing bacteria. Species such as L. crispatus, L. gasseri, L. iners and L. jensenii commonly dominate the vaginal microbiota of women of reproductive age.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
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