Two-strain probiotic supplementation ameliorates physiological responses to running in the heat

Probiotic supplementation has demonstrated mixed effects on exercise performance, with some studies showing benefits from gastrointestinal function and inflammatory responses, whilst others have not. The present study investigated the effects of a two-strain probiotic supplement on exercise performance, markers of mucosal immunity, humoral inflammation, antioxidant status, and intestinal permeability during and after running in the heat. Nineteen recreationally-trained male runners (Age: 32±8 y, Weight: 75±12 kg, VO2max: 4.7±0.5 L·min-1) supplemented with either 6 x 109 colony forming units (CFU) each of Bifidobacterium animalis ssp. lactis HN019 (Nutiani HN019™) and Lacticaseibacillus rhamnosus HN001 (Nutiani HN001™) (n=11) or placebo (n=8) daily for 4-6 weeks, in a double-blind fashion. Baseline and post-intervention running performance was assessed on a treadmill in a heat chamber (30°C, 50% RH) and consisted of 45-min pre-load at 70% of their individually determined ventilatory threshold followed immediately by a 15-min self-paced time trial. Gastrointestinal temperature, heart rate, and fluid loss were monitored during the exercise trials. Venous blood for total antioxidant status was collected before exercise; saliva samples were collected to measure IgA and blood for inflammatory markers taken before and after exercise. Intestinal permeability was also measured post-exercise. In all participants, there were significant increases in gastrointestinal temperature (∆2.0±0.4°C, reaching 39.4±0.5°C; p< 0.01) heart rate (reaching 95±5 %HRmax) and sIgA concentration and secretion (p< 0.01) in response to exercise at the end of the study period. After 4–6 weeks intervention, total antioxidant status before exercise was greater in the probiotic group (p=0.05); during the exercise test, Nutiani HN001 and HN019 reduced heart rate response versus placebo (14±12 beats·min - ¹; p< 0.01) and gastrointestinal symptoms (bloating, stomach ache, heartburn) were lower (p≤0.05); immediately post-exercise and in recovery, the lactulose:mannitol ratio—indicative of intestinal permeability—improved (p=0.01), and 8/13 inflammatory cytokines (IFNα2, IFNγ, IL8, IL10, IL12p70, IL17α, IL23, IL33) were reduced (p< 0.05); mood subscales for depression and fatigue were also lower with probiotics (p≤0.05). There was no effect of the probiotic on the distance run during the 5-min time-trial or on saliva flow rate or on sIgA concentration and secretion post-exercise. To conclude, although Nutiani HN001 and Nutiani HN019 did not increase distance-run, they improved several direct and indirect performance markers, lowering exercising heart rate, reducing exercise-induced inflammation and intestinal permeability, and increasing resting antioxidant status with usual training. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.