Exercise-induced gastrointestinal dysfunction is common amongst endurance athletes and is characterized by gastrointestinal permeability, also known as "leaky gut." Probiotics have been shown to improve gut permeability through the secretion of mucin, immunoglobulin A and improvement in stability of tight junctions between epithelial cells. This study will determine the efficacy of a probiotic containing the bacterial strains P. acidilatici, CECT 7483, L. plantarum CECT 7484, L. plantarum CECT7485) in altering markers of gut inflammation and dysfunction, and symptoms of gastrointestinal distress.

This study is a randomized, placebo-controlled, double-blinded crossover study where trained runners that experience moderate gastrointestinal discomfort with exhaustive runs will be subjected to the probiotic intervention/placebo supplementation for one month with a one month washout period. The intervention consists of the probiotic strains Lactobacillus plantarum (CECT7484 and CECT7485) and Pediococcus acidilactici (CECT7483) at a ratio of 1:1:1 at a dose of 3b cfu/day. Probiotic/Placebo capsules will be taken once daily. Biological samples and symptom data collection will be collected at baseline and after one month of probiotic/placebo supplementation. Data are also collected after an in-house treadmill run after one month of supplementation.

Inclusion Criteria:

• Males, females between 18-50 years of age
• Healthy and injury free as determined by screening questions and medical history
• Distance runners as determined by physical activity questionnaire; run = 15 miles/week, run = 3 time or more/week
• VO2max level of = 40ml/kg/min for males or = 35ml/kg/min for females
• Agree to maintain normal diet and exercise routine throughout study
• Agrees to collect stool samples as needed
• Agree to complete questionnaires, records

Exclusion Criteria:

• Women who are pregnant or breastfeeding, or plan to become pregnant during course of the study will not be included as the effect of probiotic on pregnancy and lactation is not established.
• Subjects with a known allergy to the test material (active and placebo)
• Subjects taking NSAIDs, Metformin, probiotics, or supplements that might alter the gut microbiome;these will be assessed individually. (Multivitamin and protein supplementation are allowed)
• Subject that have abnormal test results during screening.
• Alcohol or drug abuse within past year (alcohol can impair gut barrier).
• History of GI surgery within past year as it would alter the gut microbiome (excluding appendectomy and herniorrhaphy).
• Severe heart, liver, kidney, neurological, oncological or psychiatric disease, or immunosuppressed subjects will be excluded.
• Coeliac disease, inflammatory bowel disease or acute pancreatitis (all 3 can impair gut barrier)
• Regular use of antacid medication (can significantly alter microbiota)
• Subject following a low FODMAP (fermentable oligo-, di-, mono-saccharides and polyols) diet will be excluded as this dietary pattern can alter the intestinal response to exercise in some people.