Study of Blood Biomarkers in Athletes with Lower Gastrointestinal Symptoms After an Ultra-Trail Race

<b>Background/Objectives</b>: To investigate the value of intestinal fatty acid-binding protein (I-FABP), D-Lactate, interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-1 receptor antagonist (IL-1Ra), tumor necrosis factor-alpha (TNF-alpha), lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), electrolytes and creatinine in athletes with lower gastrointestinal symptoms in a cohort of ultra-trailers. <b>Methods</b>: This is a prospective study set in the ultra-trail of Puy Mary Aurillac, a 105 km race. Athletes included were given two questionnaires to collect demographic data and clinical signs related to the race. Blood samples were also collected before and 1 h after the race. Biomarker results were interpreted according to the occurrence of exercise-induced lower gastrointestinal symptoms, and whether the race was completed or forfeited. <b>Results</b>: Of the 76 runners included, 35 (45.5%) presented lower gastrointestinal symptoms. Runners that presented these symptoms had significantly higher IL-10 concentrations (8.7 pg/mL (interquartile range (IQR): 4.2-1.6)) when compared to runners without symptoms (4.8 pg/mL (IQR: 2.4-9)) (<i>p</i> = 0.01). The pre/post-race amplitude of IL-1Ra variation was greater in the group of runners with lower gastrointestinal symptoms (median: +231% (IQR: 169-551)) compared to runners without symptoms (median: +172% (IQR: 91-393)) (<i>p</i> = 0.04). Finally, the 13 (16.9%) runners who forfeited the race displayed lower AST (<i>p</i> < 0.001), LDH (<i>p</i> = 0.002) and IL-6 (<i>p</i> = 0.002) concentrations, compared to runners who finished the race. These lower concentrations were independent from running time. <b>Conclusions</b>: IL-10 and IL-1Ra could be associated with the occurrence of lower gastrointestinal symptoms.