Effects of endurance exercise on mood state and serotonin levels after thirty days of probiotic supplementation: a pilot study

The gut-brain axis relationship has been investigated in several studies in the area of health and, more recently, also in physical exercise. Changes in serotonin levels appear to be due to changes in the intestinal microbiota. Serotonin modulates brain activity and the neuropsychological processes involved in mood. In addition to its functions in the central nervous system, serotonin is also active in the gastrointestinal tract, helping in the digestive process. Likewise, the intestinal microbiota is of great importance in its concentrations, and 95% of serotonin production is carried out in the intestine. Some studies question whether these modulations can collaborate with psychobiological aspects and, perhaps, affect athletic performance. Purpose: Evaluate the effect of marathon running on mood aspects and plasma serotonin levels after probiotic supplementation in athletes. Methods: Fourteen athletes were supplemented for thirty days before the marathon. The athletes were randomized in a double-blind study model into two followed groups: placebo group (n=7; 2.0 g/day of corn starch) and probiotic group (n=7; 2.0 g/day of Lactobacillus Acidophilus, Lactobacillus Casei, Lactobacillus Lactis, Bifidobacterium Lactis and Bifidobacterium Bifidum totaling 109 CFU by strain). Blood samples were collected at baseline (before supplementation), pre-exercise (24h before the marathon race), post-exercise (immediately after), and 1h after. Additionally, pre-exercise and post-exercise, the volunteers answered the BRUMS questionnaire. To verify differences between group and time, the ANOVA two-way with Tukey Post-hoc was performed being considered p <0.05. Results: After the marathon, in both placebo and probiotic groups, fatigue and mental confusion increased, as well as vigor reduced (without significant difference between the groups; p>0.05). However, these changes were not dependent on plasma serotonin concentrations, and at different times evaluated, and between groups, no significant differences in serotonin concentrations were found. Conclusion: The supplementation of this combination of probiotic bacteria for 30 days was not effective in mitigating the mood changes generated by the marathon and did not change the plasma levels of serotonin throughout the experiment. Further studies are needed to understand the possible effects of supplementation with probiotics on strenuous exercise, such as the marathon.