The Liverpool Endurance Study

Four weeks of probiotic supplementation reduces GI symptoms during a marathon race


This randomised, double-blind, placebo controlled study aimed to assess the effect of Lab4 probiotic supplementation on gut symptoms, race time, intestinal permeability and immunological markers during marathon training and racing.


  • The study was carried out at the Research Institute for Sport and Exercise Sciences, Liverpool John Moores University.
  • 24 recreational runners (20 male, 4 female) were divided into two matched-pairs groups. The participants were matched according to their most recent marathon race time (under 5 h within previous 2 years) and BMI.
  • The first group consumed 25 billion Lab4 probiotics every day for 28 days prior to a marathon race and an additional probiotic dose on the morning of the race (2h before the start), whilst the second group took a placebo
  • After 4 weeks of supplementation, the volunteers undertook the 42.195 km marathon race on a synthetic 400m outdoor track.
  • The runners were required to complete their gastrointestinal symptom (GI) diaries at baseline, during the supplementation period, during the race and immediately post-race. Gut symptoms included bloating, nausea, urge to vomit (upper GI), flatulence, urge to defecate and stomach cramps (lower GI) and were scored from 0 to 10. Symptoms scored ³ 4 were classified as ‘moderate’ or ‘worse’.
  • Volunteers provided blood samples at baseline (4 weeks before the race), pre-race (24h before the race) and post-race.
  • Results

    GI symptoms reported during 28-day supplementation

    Gut symptoms during 28-day supplementation period

    The number of moderate gut symptoms and number of days with these symptoms were significantly reduced in the last 14 days of Lab4 probiotic supplementation compared to the first two weeks (*P<0.05).

    Gut symptom scores during each third of the race (Eur J Appl Physiol)

    Gut symptoms during the marathon race
    A significant reduction in the severity of gut symptoms was seen in the Lab4 probiotic group compared to placebo (*P=0.01) during the final third of the race.
    A signification association between gut symptoms during the race and reductions in running speed was observed, especially towards the later stage of the race.

    Reduction in average running speed (Eur J Appl Physiol)
    Lap-by-lap average running speed (Eur J Appl Physiol)

    Race speed
    Reduction in the average speed from the first to the last third of the race was significantly greater in the placebo group (14.2% reduction) compared to the Lab4 probiotic group (8% reduction, *P=0.03).


    Lab4 probiotics supplementation protects endurance runners from gut disturbances during a marathon race and may help to maintain running pace during the latter stages of racing.


    Pugh JN et al 2019.
    Four weeks of probiotic supplementation reduces GI symptoms during a marathon race.
    European Journal of Applied Physiology

    Scroll to Top