Probiotics and sports: is it a new magic bullet?

•Specific strains of probiotics appear to be effective in minimizing gastrointestinal and upper respiratory illness symptoms.•The effects are dependent on the species, dose, period, and form of administration•Probiotics effects related to upper respiratory illness symptoms are local and involve the increase of interferon-γ and immunoglobulin A•The effects related to gut comprising mainly the increase of barrier function