REF-982 · Jäger et al., 2019 · Journal of the International Society of Sports Nutrition, Vol. · Paper · PubMed

International Society of Sports Nutrition Position Stand: Probiotics

Astrong evidenceMeasured on a mixed groupWritten before October 2026, being re-checked

The International Society of Sports Nutrition reviewed how probiotic supplements work and how athletes use them, ending with ten conclusions. Most research concerns gut and immune health, and benefits depend on strain and dose.

Among athletes, particular strains can cut the number, severity and duration of upper respiratory tract infection episodes, can strengthen gut-barrier integrity, and certain strains can raise uptake of nutrients such as amino acids from protein. Selected anti-inflammatory strains have been linked to better recovery after muscle-damaging exercise.

The effective dose depends on validation studies of the specific strain. Other proposed benefits (body composition, testosterone, cortisol, lactate, cognition and mood) rest on preclinical and early human research and still need to be validated in athletes and in more rigorous human studies.

Participants

Not applicable (position stand). Written by an author panel for the ISSN.

Protocol

Objective and critical review of the available literature on the mechanisms and use of probiotic supplementation for the health, performance and recovery of athletes; conclusions stated as ten numbered points.

Key Results

Definition: probiotics are live microorganisms that benefit the host's health when given in sufficient amounts (FAO/WHO).
Most researched: gut and immune health.
Strain- and dose-dependent: despite shared core mechanisms, health benefits are strain- and dose-dependent.
Athletes' microbiota: its composition seems to mirror how active the person is, mainly tied to exercise volume and protein intake; it is unknown whether these differences change how well probiotics work.
Absorption: some strains can boost uptake of key nutrients — amino acids from protein, for example.
Immune: approximately 70% of the immune system sits in the gut; among athletes, specific probiotic strains can cut how many upper respiratory tract infection episodes occur, and how severe and long they are.
Gut barrier: intense and prolonged exercise, particularly in the heat, raises gut permeability; specific probiotic strains can strengthen gut-barrier integrity in athletes.
Recovery: selected anti-inflammatory strains have been linked to improved recovery from muscle-damaging exercise.
Dose and label: the minimal effective dose and method of administration depend on validation studies for the particular strain; products must state genus, species and strain and the quantity of each strain at the end of shelf life, as colony forming units (CFU) or live cells.
Unproven: body composition and lean mass, testosterone, cortisol, exercise-induced lactate, neurotransmitter synthesis, cognition and mood — preclinical and early human research that requires validation in more rigorous human studies and in an athletic population.

Practical Application

"Should I take a probiotic?" The ISSN position stand (Jäger 2019, A) says the best-supported uses in athletes are fewer and milder upper respiratory tract infections and a better gut barrier — with specific strains only, at the dose validated for that strain. It names no strain or dose in its abstract and does not claim a performance gain.
"A probiotic" is not a prescription: a product is only as good as the trial behind its exact strain, and the label must name genus, species and strain with a CFU count at end of shelf life. A product without that is not what the stand describes.
Gut-barrier integrity is a marker, not a symptom: the abstract does not say probiotics reduce gut symptoms in training or racing. For symptoms, the tested route is rehearsing the intake (REF-979, REF-980).
Read with the authorship in mind: many of the authors declare employment by, or funding from, the probiotic industry (conflict-of-interest statement on the record).
Not from this paper: where probiotics sit among supplements with a case is SYNTH-67; the gut-symptom framework is SYNTH-08.

Limitations

A position stand from one society; conclusions are narrative, with no pooled effect sizes, no named strains and no doses in the abstract.
Extensive industry ties among the authors (declared).
Several listed benefits are explicitly preclinical or early human research.
The abstract makes no statement on endurance performance or on gut symptoms during exercise.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

major position stand from a sports-nutrition society; a critical review, not a meta-analysis: no pooled effect sizes, no named strains or doses in the abstract, and many authors with probiotic-industry ties