Exploration of Gastrointestinal Integrity, Systemic Immune Response, and Exercise-Associated Gastrointestinal Symptoms in Adolescent Athletes in Response to a Single-Stage Ultramarathon: A Case Series Approach

This case series aimed to observe the impact of a single-stage ultramarathon (50-100 km) on gastrointestinal integrity, systemic immune responses, and exercise-associated gastrointestinal symptoms in 3 adolescent (aged 12-15 y) competitors. Body mass, venous and finger-prick blood samples and fecal samples were taken before and after the race for analysis of exercise-induced body mass loss, plasma osmolality, plasma intestinal fatty acid binding protein, soluble CD14, and C-reactive protein, total and differential leukocyte counts, and fecal bacterial alpha-diversity. Gastrointestinal symptom incidence were recorded before, during, immediately after, and 24 h after the race. Food and fluid intake were recorded for the 48 h before the race and each hour during the race. Body mass decreased in Youth 1 (-0.4%) and Youth 3 (-0.9%) and increased in Youth 2 (+0.5%) from before to after the race. No youth competitor met carbohydrate intake recommendations in the lead-up to (2.8-5.1 g·kg^-1·d^-1) or during the race (24-26 g·h^-1). Pre- to post-race plasma intestinal fatty acid binding protein and C-reactive protein concentrations increased in the youth competitors, but was of no clinical significance (≤657 pg·mL^-1 and ≤3.36 micrograms·mL^-1, respectively). A pre- to postrace change in plasma soluble CD14 of clinical relevance was observed in Youth 3 (1.5 micrograms·mL^-1), but not Youth 1 (-0.1 micrograms·mL^-1). Total and differential leukocyte counts increased beyond the normal reference range in Youth 1 and Youth 2, but not Youth 3. The incidence and severity of gastrointestinal symptoms were low at all timepoints in the competitors. Large intra- and interindividual responses to ultramarathon events observed in this case series suggest that adolescent ultramarathon runners require individually tailored nutrition support.